Building Better Worlds in the 21st Century

Dani Eder,

The Seed Factory Project,

6485 Rivertown Rd, Fairburn, GA, 30213

email: danielravennest@gmail.com

May 2023

Note: Most of this report is now part of the more detailed two volume Better Worlds set.

 Introduction - Current national space programs are based on a limited vision of going to one place at a time for reasons like science and national prestige. Missions have finite goals and end when they are reached, so they don't include full development of the destinations. Instead, equipment and supplies come from Earth, which keeps costs high. Limited goals and high cost result in poor return on effort.

 In this report we propose a broader concept of upgrading and extending civilization on Earth first, then full development of the entire Solar System, and eventually beyond it. Our approach is based on self-improving production systems that grow from a starter set of core equipment called a Seed Factory. Seed factories make more equipment for themselves mostly using local energy and raw materials. This is in addition to making finished products like any other factory.

 Each location follows a growth cycle of self-improvement, making products for local use, trade with the rest of society, and becoming economically self-supporting. Once matured, the location sends elements of new starter sets to new locations. Locations are developed in logical progression from easier to harder and more distant.

 The very large physical space, materials, and energy resources beyond Earth enable large total returns. Since locations grow to support themselves, the net cost of such a program is only the initial start-up, so the return on effort is high.

 It isn't in the scope of this report to provide detailed plans and hardware designs. What we describe is a possible path that leverages self-improving production methods. This is a step towards solving existing problems and building a better future, but much more work is needed for this idea.

1.0 - Problems of Current Programs

 

 Governments have pursued space projects and programs, individually or in groups, for purposes like research, exploration, advancing technology, and prestige. While the results can be large, these efforts often suffer from outdated assumptions, high absolute costs, low relative return on effort, and a focus on single destinations. They have also often not leveraged new knowledge and technology.

Outdated Assumptions

 Sending people to the Moon and Mars are stated goals of US National Space Policy. Significant annual budgets are being spent towards these goals, primarily on the Space Launch System and Orion Spacecraft. The program concept to reach these goals is directly descended from plans first made in the mid-20th Century, such as Von Braun, 1954. In the decades since, the technologies to be used have advanced, but the overall concept has not. In NASA's Journey to Mars (Oct 2015), the "mission" approach includes a number of assumptions:

• It is a round trip for the crew, from Earth to Mars and back, with limited duration on the Martian surface.
• Because the number of missions is small and they are short, it is not economic to develop many local resources.
• Most or all equipment and supplies are launched from Earth.
• High cost limits mission mass. So crews have to accept risks from radiation exposure, equipment failure, and lack of fallback positions.

 Other goals like the Moon and orbiting stations have similar limiting assumptions, and are considered separately from each other.

High Cost

 Government-funded and contractor-built space programs have little incentive on either side to finish promptly or keep costs under control. Project-oriented agencies want to continue their existence, but getting approval for new projects is hard. Contractors want to earn as much as possible, but winning new contracts by competitive bidding is uncertain. Politicians who decide on budgets want to preserve jobs in current locations, which works against cost savings.

 The incentives on all sides have led to low cost estimates to get project approval. The tacit understanding is real costs will gradually be revealed as the work progresses. Spent funds deter cancellation as the full costs are revealed, because the funds would then be wasted on an unfinished project. This pattern avoids frequent approval for a new project or competing for new work. The project schedules are instead stretched to fit real cost to available annual budgets. The result is a few big "can't fail" projects. Public failures risk losing funding or even an agencies' existence. So projects must be conservative, slowing progress.

Low Returns

 In terms of exploration and science, a trip going to one place like Mars, and bringing back perhaps a few hundred kg of samples, is not much return for the effort expended. Relatively short round trips do not allow for full exploration of a landing site, much less a planet with the land area of Earth. Lack of refueling stations and reusable vehicles limits sample mass that can be returned to Earth, where researchers and laboratories can fully analyze them.

 If most items have to be launched from the deep gravity well of Earth, then delivery costs will be high, and increase linearly with the number of missions. High transport cost limits weight, and in turn safety features like adequate radiation shielding, backup vehicles, and spare parts and supplies. To minimize risk, what is built must be both lightweight and near-perfect, which is also expensive. Despite that, crew risk is still high in absolute terms. The combination of low return and high cost have delayed going to the the Moon and Mars for decades. Such a program is now moving forward, but very slowly.

Focus on the Moon and Mars

 The Moon is nearby, big, and obvious to everyone on Earth. So it was a natural first destination for human exploration. Venus and Mars are the closest major planets. Venus was originally thought a suitable destination because of similarity of orbit, mass, and gravity. However it turned out to be very hot from a thick CO2 atmosphere. Mars then became the next focus of human exploration by being the most Earth-like and nearby destination.

 The focus on Earth-like conditions ignores that on Earth, even the best places require some technology to survive, and more of it to be comfortable and flourish. At a minimum clothing, shelter, and agriculture, are needed, with their underlying technologies. For most of the Earth technology like ships, planes, and snow crawlers are needed to reach places, and more technology if you intend to stay.

 Mars, or anywhere else in space, also require technology to survive and flourish. But Mars does not require dramatically more than harsh places on Earth. For example the temperatures on Mars overlap those of cold places on Earth, such as Siberia and Antarctica. At the same time, the surface of Mars isn't less difficult than other locations in space. Getting there needs more work than high orbits near Earth. The colder surface temperatures and 80% lower solar flux require more equipment than near Earth. A primary focus on the Moon and Mars over everywhere else is a mistake. They are large, interesting, and can be useful. So they should be part of future programs, but not to the exclusion of other places.

 A new approach is needed that remedies the problems noted above. It should be based on up-to-date knowledge of the Solar System and new technologies developed since the mid-20th century. It should explore and use all of the many places in the Solar System. That includes the orbital and interplanetary spaces around and between natural objects. Finally, it should have high science and economic returns for the effort expended, including direct returns to people on Earth.

2.0 - New Knowledge and Technologies

 

 Our new approach starts with a modern overview of the Solar System and its resources. We then introduce technologies to access and use those resources. Self-improving production systems that become highly efficient with "Smart Tools" is key among these. Our intent is to use these to benefit civilization and the Earth's environment.

2.1 - The Modern Solar System

 

 The mid-20th century Solar System included 9 planets and their moons, plus a few thousand asteroids in the belt between Mars and Jupiter. Materials would be available on the surfaces of the Moon and Mars, but required significant fuel to take elsewhere. So they would only be used locally. Energy would come from solar-powered steam turbines, or a little later from fuel cells. These ideas are quite outdated and becoming more so each year.

 Today we can inventory at the known Solar System in terms of its material and energy resources. Such Natural Resources on Earth are well-studied and understood. Most people know about the Moon, the other major planets, and that some of them also have moons. So here we will mainly review the more recently found and less familiar parts Solar System.

 In terms of resource access, the smaller members of the Solar System all take less energy to land on and remove materials from than Earth. They also have greater surface area relative to mass and lower gravity, making extraction easier.

Material Resources

 Near Earth Objects (NEOs) are those which come closer than 1.3 AU to the Sun, where 1 AU is the Earth's average solar distance. Mars' orbit ranges from 1.38-1.67 AU, so NEO's are "on the way there" in terms of solar distance. In 1950 time there were 55 such objects known, of which only 13 were asteroids. The rest were comets, which are easier to find when they have large tails. The asteroids were ignored because their orbits were not ideal, and mining them was still a subject for science fiction.

 This has changed dramatically. As of early 2023 there are over 31,500 known NEOs. The number has increased exponentially since about 1980 as better telescopes have been used to find them. These searches are partly driven by the impact risk such objects pose to Earth. Of those found so far, 853 are asteroids 1 km or larger in size, a nearly full count. 10,400 are larger than 140 meters out of an estimated 27,000 total. The rest are smaller, with perhaps 4 million yet to find larger than 10 meters (Trilling, 2017). 119 of them are comets, which lose material when close to the Sun. Just the largest handful of NEOs have a combined mass of 50 trillion tons, which is roughly a thousand years of mining activity on Earth.

 The much larger numbers means more of them are in orbits easy to reach from Earth or on the way to Mars. Very efficient Electric Propulsion and other technologies unknown in 1950 time now exist. They make it possible to reach NEOs and work with them remotely from Earth, as recent asteroid and comet probes have done. Early research has been done on Asteroid Mining and Space Manufacturing to make use of their materials. Using NEOs as sources of propellants, supplies, and other products would greatly reduce what you need to bring from Earth for space projects.

 Beyond those that come close to Earth, the Total Number of known objects in the Solar System, as of 2023, is 1.27 million. This is about 600 times what was known in 1950. The list of such Minor Planets has grown rapidly as new dedicated telescopes and search techniques were applied.

Figure 2.1-1 - Inner Solar System objects.

 92.3% of known objects are in the Main Asteroid Belt between Mars and Jupiter (Figure 2.1-1), but many thousands of others are in orbits throughout the Solar System. The Minor Planet Center maintains information about all of them. The high proportion in the Asteroid Belt is a function of distance, not absolute numbers. Brightness decreases as square of both distance from the Sun and the telescope. So discoveries are strongly biased to nearby objects, and to only finding the largest ones at greater distances. But total number of objects goes up about 3,500 times when the size goes down by 100 times. So there are many more smaller objects still to be found.

 Many of the objects discovered beyond Neptune, at 30-80 AU, have Eccentric Orbits. These objects tend to be found at the close end of their orbits, when they are bright enough to see. This additional discovery bias means there are many more like them waiting to be found, but are currently in more distant parts of their orbits, or never come close enough to find with current telescopes. The 2023 count of about 4800 such distant objects is limited to those larger than 100 km for the farthest ones. As search methods improve, many more such objects will be found at all distances and more of the smaller ones.

 Near-Parabolic Comets can reach distances measured in light-years, or even escape the Solar System entirely. Aside from them, the known size of the Solar System has increased nearly 64 times since 1995, from 49.3 AU for Pluto to 3136.5 AU for the maximum distance of scattered object 2014 FE72. Some of these objects are quite large (Figure 2.1-2), and there is even a suspected major planet still to be found. Although the absolute distance of these objects is very large, the energy to reach them has a finite limit, as the five planetary probes Leaving the Solar System demonstrate. The practical limit is set by how long it takes to reach and use them.

 The inventory of Solar System objects is now known to be incomplete, especially for small and distant ones. Despite this, there is detailed knowledge of the history, composition, and geology of some of its members, and this is constantly improving. We expect this to continue, especially from future mass-produced probes with efficient propulsion and refueling capability. Many more objects can then be visited than the current handful per decade. As more is learned about these objects, better plans on how to use them can be made. But even with current knowledge, a start on such plans is possible.

Energy Resources

 The Sun is an immense energy source, producing 20 trillion times what civilization uses today. That energy streams in all directions, not just at the objects which orbit it. Mining and building on the surface of Solar System bodies is convenient, but they typically gather half or less of the available solar energy. This is because of day-night cycles, geography, and in some cases atmospheres and eclipses from other bodies.

 It takes significant energy to move materials from the larger bodies to open space, but once there, solar energy is available up to 100% of the time. For example, with current technology it takes about 480 MJ (134 kWh) to raise 1 kg from Earth to an orbit in full sunlight. Once there, 1 kg of modern space solar panel can extract that much energy in 56 days, but lasts about 100 times longer. Most solar system bodies are smaller than Earth, and there are more efficient ways to lift materials than today's rockets. So from a net energy standpoint it often makes sense to work in open space.

 Solar cells were only 6% efficient in the mid-20th century, so solar-driven steam turbines were part of the original Mars mission concepts. Solar cells are now 47.6% efficient in the laboratory and 31% for space power applications, and continue to Improve. Using lightweight concentrating reflectors, they can be useful even in the outer Solar System. Where heat, rather than electricity, is needed, direct solar exposure or using mirrors can can reach 80% efficiency or higher.

 In addition to solar, there are various energy sources that are more limited in scale and location. These include nuclear fission and potentially fusion, geothermal, and wind. On Earth we use hydroelectric and chemical combustion, but those are not generally available elsewhere. The orbital motion and gravity fields of bodies are not energy sources, but their potential and kinetic energy can be used in various ways. The Sun's output alone, which will last for billions of years, plus raw materials found all over the Solar System, are enough to sustain civilization and the Earth's environment.

The Illusion of Scarcity

 Current civilization is actually quite limited, even on Earth. The urban, forest, and farm land used in any significant way amounts to only 13.5% of the planet's surface. The remainder are oceans, deserts, and ice caps that are only traveled through or barely used. Of the part that is used, it is equivalent to a thin surface layer.

 The world's biosphere (about 2000 Gigtons) plus the human built environment (about 1100 Gigatons) averages about 6 kg/m², while the Earth's total mass to area is 11.71 billion kg/m², or a ratio of one part in 2 billion. At the density of water, the biosphere plus civilization amounts to a 6 mm (1/4 inch) thick layer across the planet's surface. If we only consider the fraction of the planet used, the equivalent thickness is 7.4 times higher, or 4.4 cm (1.75 inches). If this number seems small, it is because most of us live in places that are built up. Life and civilization are very unevenly distributed. Cities and river dams, for example, have much higher built mass per area, while tropical forests can reach 25 times the average biosphere density per area.

 The perceived scarcity of resources is an illusion, because current civilization uses only 2 billionths of the planet's mass and one ten-thousandth of the available energy flow. Photosynthesis uses about 13 times more available energy, but still only about 1/8%. In a literal sense we are only scratching the surface of our own planet. When we consider the whole Solar System, the available resources increase by hundreds of times in mass, and two billion times the energy that reaches Earth.

 A larger fraction of smaller bodies is accessible. On Earth pressure and temperature limits going too deep. Bodies with lower gravity and less hot interiors can be accessed more deeply or all the way through. The much higher total energy across the Solar System would also allow reprocessing and reusing what we consider waste products today. Scarcity would not be a problem if these vast untapped resources could be used.

2.2 - New Technologies

 

 For our approach we want to use the best available production and space technologies, plus some new ones that can be developed in the near future. These include seed factories, production networks, space technologies that are already in use but not yet in government plans, and new ones for space not yet fully developed. This is in addition to more standard existing technology.

Seed Factories

 Production systems which use part of their output for self-improvement can grow exponentially. Production can start with simpler tools, but modern technology like computers, communications, automation, robotics, software, and artificial intelligence lets them become more efficient.

 We call a starter set of tools and machines capable of self-improvement a Seed Factory. They grow to become mature factories by analogy to plant seeds, which grow into mature plants that can produce more seeds. Seed factories can improve in several ways:

• Making parts for additional copies of current equipment.
• Making new types of items not in the starter set, and
• Making different versions of existing equipment (larger, more accurate, etc.).

 While modern technology can reduce the labor needed, some people are still needed today to operate the factory. Like any other factory, some part of its output is for sale or trade. This helps cover the initial cost and items it can't make internally.

 The improvements increase production capacity and the range of products that can be made. Since the capacity to grow increases with the size of the factory, the growth is exponential. The starter or added equipment can include power generation, mining, and materials processing, so the factory can self-supply and self-power from local resources. A seed factory may not use any local sources to start with, but can approach 100% as it matures. Some parts and materials would likely be too hard to make, or too rare locally. So even for a mature factory they would still come from elsewhere.

 When production at a given location is mature enough, it can start supplying parts for, or complete new starter sets. These can be set up locally or sent to new locations, repeating the growth process. Internal growth and making new starter sets highly leverages the initial cost. It fundamentally changes the return/cost ratio of projects for the better.

Locations and MakerNets

 When we refer to "locations" we mean a single environment type, with equipment and people that are close enough that they can work together and trade physical items easily. On Earth that might be a single metropolitan area. In less developed places it might be smaller in size from lack of easy local transport. Equipment in a given location may have different owners or control systems, but can still coordinate their work and cooperate on larger projects.

 The collection of coordinating operations forms a network, which we call a MakerNet, after the modern Maker Subculture, who make things. The network has multiple communicating nodes, each of which includes a set of equipment and people who can do tasks. A MakerNet can extend over multiple locations, since data transfer and remote control can operate over long distances at low cost.

 Physical transportation of people and supplies is not as easy, so we distinguish separate locations within a larger network. To the extent local sources can be used, it would lower transport costs. So there is an incentive to ship lightweight items like information over bulk materials.

Space Technologies

 New or improved space technologies have been developed since the mid-20th century, but not fully included in program plans. These include:

• Electric propulsion - which uses many times less propellant than chemical rockets. Using large tanks of propellant to deliver relatively small payloads has strongly limited space projects in the past.
• Better Materials - There are new and significantly improved engineering materials, including high strength fibers, and composite materials that use them. Production methods for them have also improved.
• Closed Loop Life Support - has been developed which recycles supplies using mechanical equipment or biology.

 Additional technologies that were not specifically developed for space, but can be used for it, include small and powerful computers, their software, other kinds of electronics, robotics, automation, high speed communications, and most recently artificial intelligence (AI) applications.

 Many other space technologies have been proposed, but not yet fully developed. This is either from lack of money and resources, or not enough scale yet to justify them. MakerNets and seed factories can potentially overcome these limitations. Our second volume on Space Systems Engineering collects current and future space technologies that we know of, so they can be considered for future plans. Some transport examples are ground-based accelerators and air-breathing engines for reaching orbit, and rotating skyhooks for artificial gravity and orbit transfer.

3.0 - New Program Concept

 

 For discussion purposes we refer to this as a program, with component phases and projects. But we do not expect it to all be under centralized government direction. Instead it would also include independent businesses operated for profit, public/private partnerships, incentive prizes, and other alternatives.

 This section summarizes our goals and approach. The rest of this report, and our other documents, provide more details. This is a work in progress. It is by no means a finished proposal or a final design. It likely never will be, as the future brings new discoveries and technologies. We have identified new goals and methods, and made a start at the details, but much more work is needed. Our work is open-source, so feel free to build on it, provide feedback, and contribute your own ideas.

Goal 1 - Benefits on Earth

 Existing government space program goals are mainly for science, exploration, and national prestige. They have limited budgets because they compete with other government priorities. Our approach is to go beyond these limits, to include the full range of civilized activities, both on Earth and in space. About billion times more people live on Earth right now than in space, and their needs are much larger and more immediate. So our first goal is to address problems on Earth, starting with easier ones and then towards the more difficult.

 Competition and profit incentives have often demonstrated faster and cheaper results, so we want to take advantage of them. If there is money to be made, there is a vast pool of capital available beyond agency budgets. The $386 billion Global Space Economy (pdf file) in 2021 was already mostly commercial activity, and 16.5 times NASA's budget.

 The original 1982 Version of the seed factory idea was intended to enable large space projects by production in space. But the laws of nature and how technologies work are the same everywhere. If networks of exponentially improving and multiplying systems can work in space, they will work on Earth too. The operating environments, local raw materials, and energy sources may differ by location, but the underlying principles are the same.

 The early versions of seed factories would most likely be built in higher income areas. These are the easiest places to start because equipment, materials, and energy sources are readily available, as are people who know how to work with them. Self-built and self-owned production can supplement or replace conventional work for hire. Such jobs have always been at risk from economic and business changes. In the future they may be permanently replaced by the same kinds of advanced technologies seed factories can use.

 As the owners of production capacity, people can more securely meet their basic needs. They get the benefit of the output regardless of how much labor is replaced by technology. Self-improving systems can grow to mostly copy themselves, so they would become low cost to build. They can also become highly automated and use renewable energy, making them low cost to operate.

 The growing network of productive systems can then be extended to lower income areas on Earth. This allows bypassing fossil fuel development and the problems it creates, while gaining the comforts, health, and safety found in higher income areas. The systems can be further extended to difficult and extreme locations on Earth that are currently unused or barely used. This would lessen scarcity of raw materials, further lowering cost of operation. These expansions and upgrades should be done with planning and care to prevent new environmental side-effects.

 Although we describe a progression from easier to harder locations, a given type of location does not have to be completely developed before starting the next category. Rather, their starting points are staggered in order of difficulty, and their development then continues in parallel.

Goal 2 - Benefits from Space

 Economic and environmental reasons are enough reason to build self-improving systems on Earth. Once there is enough experience with them, they can then be used in a series of locations in space. There are several reasons for this:

• Access to materials on Earth is limited vertically because temperatures and pressure increase with depth.

• Solar energy in nearby space averages 7 times more than the Earth's surface because there is no night, weather, or atmospheric absorption.

• Different and much larger amounts of materials are accessible, which can be used without affecting the Earth's environment.

• There are a variety of risks to civilization on Earth, both natural and self-created. Some of them can be reduced by projects in and expansion into space.

 So our second goal is to make use of space to bring benefits to Earth, and later extend civilization and the biosphere into the space environment.

 Space projects would logically start with easier and nearby locations, then move to farther and more difficult ones in sequence. Developing a new location begins with imports of equipment from Earth or previous locations. Core production and resource extraction is built up, then expands to other kinds of industry. Later deliveries of materials, products, and services helps support operations.

 Remote control is feasible when distances are short, or command-response times can be long. But in other cases some people are likely needed on-location to set up and maintain equipment. Suitable locations can build up habitats beyond this for other reasons. Once built up enough, an existing location, along with previous ones, can serve as staging points for the next one, supplying transportation, starter sets, and other items as needed.

 Space locations vary in environment, raw materials, and energy resources. So a trade network among them and the rest of civilization makes sense, just like it does on Earth. Each location takes advantage of local conditions to do what it can do best, and trade with others as needed. Through trade, locations can become economically self-supporting and not a cost sink for society.

Program Advantages

 Our new approach has a number of advantages:

• It addresses the frequent criticism of space programs that there are problems here on Earth that need solving. So we place solving economic and environmental problems first, ahead of large space projects.

• Self-improving and highly automated production lowers the cost of rocket factories and launch sites. It also lowers how much you need to launch by using local space resources. The combined result is much cheaper space projects. Activities that are currently uneconomic can become viable.

• In terms of science and exploration, access to the whole Solar System is better than just the Moon and Mars, as interesting as they may be. Locations develop their local resources, so they can sustain long-term operations, rather than being limited to short term missions and single landing sites.

• It is much safer than isolated missions. A network of many locations can keep backup supplies and equipment available, and they can be delivered more quickly. Automated and remote controlled transports can deliver supplies and equipment before the first people arrive, and regularly afterwards, providing a buffer against problems.

• Lower production and transport costs means more robust designs can be used. Current space systems minimize weight to save on launch from Earth. Robust designs will have better safety margins, lowering crew risk. Bulk mined materials, either in raw form or as end products, can provide radiation shielding during long missions. Production capacity at the destination, such as the Martian surface, enables making spare parts and replacement supplies on the spot, bypassing long delivery times from Earth.

3.1 - Program Sequence

 

 Our program concept is organized into a number of phases and smaller individual projects. There are several reasons for this:

• The phases have different scales of operation, or use locations with different operating environments, raw materials, and energy resources. They will need different designs suited to them.

• We intend each phase to economically justify itself, and provide revenue and benefits to support later ones. It would take too much funding for such a large program otherwise.

• New technologies need more development before using them for seed factories, makernets, and various space projects. This will not happen all at once. Splitting up the research and development across phases and projects is more manageable.

• We can lay out a long term program now, but we don't know what new technologies will be invented in the future, or when. Later phases can be identified for guidance and direction, but it makes sense to concentrate on the early ones for now. Details of later phases can be left flexible until their time approaches.

Figure 3.1-1 - Program Phases vs Time.

 In general, phases don't end, but rather build on previous ones and operate in parallel once started (Figure 3.1-1). For example, mature industrial factories will continue to operate once new locations are set up elsewhere. The phases have a logical sequence, where later steps generally depend on earlier ones. We have identified seven main ones numbered 0 to 6, shown in different colors, with a number of sub-phases indicated by an added letter (4A, 4B, 4C, ...).

Figure 3.1-2 - Logical sequence of program phases.

 Figure 3.1-2 diagrams the logical relationship of phases. It does not show all their relationships, since that would make the diagram too complicated to read. Their general order is from easier to harder, and from local to more distant. Each phase typically involves multiple projects and locations. For example Phase 5B - Mars Surface Locations, would eventually include many projects across the planet. Most locations will evolve across time by expansion and upgrade. The phases are summarized in the next two headings (3.2 and 3.3), and then in more detail in sections 4 through 9.

3.2 - Phases 0 to 3: Earth Locations

 

 Our program in the broadest sense changes the goal from specific destinations, like a mission to Mars, to improving and extending civilization and the biosphere throughout the Solar System and beyond. We start with our own planet first, because there are large and immediate needs here. So the first four phases apply to Earth.

 Much of human civilization is unevenly developed and unsustainable, and the vast majority of people will live here for many decades. Starting on Earth allows getting experience with technologies that will later be used in space. It is easier and less expensive to apply them here first, and they can produce economic benefits to sustain themselves.

 This program would widen participation from the U.S. national space program, or a joint effort of several national programs, to all of civilization. The NASA budget is about 0.025% of gross world product, and only part of that is devoted to exploration and science beyond Earth. Being more inclusive increases the available inputs for projects, and makes faster progress in the end. The first four phases are:

 Phase 0: Research and Development - The first major phase performs necessary research and development (R&D) for production technologies to be used on Earth, later adaptions to space, and ones used only in space. It also develops transport, habitation, and service technologies as needed for the particular conditions of different locations. The R&D work is spread out in time according to which phases, locations, and projects particular designs are needed for. Some later R&D, such as testing hardware in the operating environment, would occur in space.

 Phase 1: Starter Locations & Network - This phase builds the first sets of seed factory equipment and begins the self-improvement process. Phase 1 equipment can start small, such as home and hobby use, which makes it affordable. Individual equipment items or small groups of them can be located at home or shared work spaces. A network of people directly or electronically coordinate their work to make items for each other, build new network nodes, and start to accumulate larger shared items. New locations may start with less than full starter sets, and build up to making internal improvements. Phase 1 locations are typically in developed and populated areas with access to the materials, energy sources, and equipment needed.

 Phase 2: Distributed and Industrial Locations - One of the ways a seed factory can grow is to use existing machines to make parts for larger machines. This leads from home and hobby size, to small business, commercial, and industrial scale equipment and locations. At smaller scales it is reasonable to gather the full range of equipment and people in one place, and make a wide range of products. At larger scales, the equipment and their operators tend to become more distributed and specialized, and serve larger markets. But they can still coordinate on projects and products.

 Phase 3: Difficult and Extreme Locations - This phase begins extending life and civilization to the parts of the Earth where there is very little or none today. They are unoccupied partly because the environment conditions are more difficult. Self-improving production allows operating affordably in such places. New systems would be set up and grow serially from moderate to difficult and more extreme environments. Technologies like automation and remote control allows machines to operate where it is not feasible for people to stay.

 A major direction for expansion is vertically, to access additional resources and physical space. This goes beyond the fairly thin current layer of activity near the Earth's surface. We can expand the total active area by 7.4 times, but height can be increased hundreds or thousands of meters both up and down. This enables many times more usable volume and materials.

3.3 - Phases 4-6: Space Locations

 

 The later parts of our program involve developing and using space to benefit Earth. It would be based on experience gained in the earlier phases with self-improving systems which can make more such systems. It is also based on the larger production capacity developed in Phases 2 and 3. This capacity enables building transport systems like rocket factories and launch sites, and plus equipment and starter sets to be used at the new locations. The experience in working in remote and hostile environments in Phase 3 can also be applied to the remote and hostile environments of space.

 At a civilization level this accesses the much larger physical space, energy, and material resources beyond Earth. Some heavy industry can eventually be moved to space locations, protecting the Earth's environment. It can also decrease societal risks by, for example, diverting hazardous asteroids, or filter parts of the solar spectrum to reduce overheating the planet.

 As in the earlier phases, we propose a step-by-step approach: extracting local resources, building up core production, diversifying industries, then sending starter sets to the next locations. Locations become physically and economically self-supporting, allowing moving forward to new ones. The three later main phases are:

 Phase 4: Orbital Locations - Locations in this phase share being in orbit around Earth, or in open space between large bodies. This is in contrast to the the surface or closely bound bound orbits around those bodies. The sub-phases progress from lower to higher Earth orbits, then in distance from the Sun from closer to more distant.

 The main local raw materials are from asteroids and other small bodies, but we can import additional material from Earth, the Moon, and other places. We can also mine a limited amount of the Earth's upper atmosphere and the "debris belt" of discarded space hardware. Solar energy is abundantly available in the open spaces near the Sun, but other solutions become more important in the farther areas.

 Phase 5: Planetary System Locations - These locations are orbits tied by gravity to the Moon, major planets, and their larger moons, or on their respective surfaces. The sub-phases are by distance starting with the Moon, then to the inner and outer planets. Although orbital and planetary locations share features like vacuum or atmospheres we can't breath, they differ in having significant gravity wells or surface gravity, and in having night or time in shadow from the Sun. These differences require different designs, so we place them in a separate phase. Mars is part of this phase, but has long-term and larger scale exploration and development, rather than a few short missions.

 Phase 6: Interstellar Locations - The last major phase of extending life and civilization includes the space between stars and locations bound to other stars. This is mostly speculative right now because it is far away in time. A lot new technology will likely be needed, and what will already be developed by then is unkown. We see no reason to stop just because the edge of our Solar System is reached. For now, technical feasibility limits how far projects can go. But that may change in the future, so we include this final phase as a place-holder, and to provide a direction to plan for.

4.0 - Seed Factory Technology

 

 Our program leans heavily on the idea of self-improving production from starter sets (seed factories), so it deserves some details here. More on the subject can be found in Volume I, and information about Our Project, which is attempting to develop the technology.

 Tools and Growth - Humans have always been able to use tools to make more tools. This goes as far back as the Paleolithic, 2.6 million years ago, when hammerstones were used to flake other stones to produce an assortment of tools. In modern times we use metal-cutting Machine Tools to make parts for more machine tools, plus all the other kinds of machines used to make other products.

 What is new about seed factories are starter sets purposely designed to make parts for more equipment to improve the set. This can include supplying its own energy and raw materials to operate. There are several ways to improve:

• Replication - making copies of existing parts and equipment,
• Diversification - making parts for new equipment not in the current set,
• Quality - making items stronger, more accurate, or from different materials, and
• Scaling - making different size parts (usually larger) than the current ones.

 A relatively small starter set can then grow to produce a wide range and large quantity of products. This can include parts for new starter sets. A starter set may not be able to copy most of its own parts at first, because it lacks the right equipment. After following a planned series of upgrades, though, it can gain the ability to reproduce the original set.

 This approach substitutes information, like plans and instructions, for some part of a mature and more capable factory. On Earth this reduces the cost to get started. For space projects it reduces the starting weight and size, making delivery to distant places easier. With modern technology, the information can be stored and transmitted efficiently, and Smart Tools (software, robots, etc.) can do much of the work. However, growing from a starter set will take more time than immediately building a finished factory.

Self-Replication and Distributed Production

 A seed factory is not the same as a Self-Replicating Machine. First, a number of different materials and production processes are needed to make modern equipment. These are best carried out by separate tools and machines designed for each task. For large-scale production the set of equipment will be closer to commercial building size, and better described as a factory than a single machine.

 Second, a starter set can be much smaller and simpler than the mature factory. We think of it as the seed from which a factory grows. But a plant seed is not the same as the mature plant, so this is not direct replication in the sense of making an exact copy. If a mature factory can produce new starter sets, it is indirect replication by a cycle of growth and then making copies. This is more like plants and animals reproducing by way of smaller and simpler offspring.

 Third, starter sets and the mature factories are not generally able to make everything they need by themselves. At first they will lack all the right equipment. Even when mature there will likely be items too hard to make, or too rare locally. Those need to be supplied from elsewhere. Since they cannot do it all by themselves, they are not fully self-replicating.

 Traditional factories and workshops had to bring the equipment and people to one place, because it was the only way to coordinate the work. With modern computers, software, and communications this is no longer required. Equipment in different places can work together, and people can operate them remotely. So a modern view of factory capacity is the ability to make things on a regular basis. The people and equipment may be in one place for efficiency, but they don't have to be - they can be partly or entirely distributed. What's important is they can work together to make desired products.

Operations and Functions

 Production in general involves a number of processes. A seed factory may not do all of them at the start, but they can be added in steps as it upgrades. They include:

• Control of operations - collecting data and sending instructions to the various people and equipment.
• Supply power - this includes electricity, thermal heating, and other sources.
• Extract materials - mining and harvesting raw materials.
• Process materials - converting raw materials to usable inventory.
• Fabricate parts - use inventory stock to produce finished parts.
• Storage and protection - house inventory in various stages of production, plus protect equipment and inventory from local conditions when needed.
• Assemble elements - combine finished parts and materials to produce completed products.
• Grow organics - such as food and timber. These can grow on their own given the right conditions, making it different from other kinds of production.

 Most production flows need materials and energy to work with, in addition to tools and machines. In developed areas these can come from outside sources. In less- or undeveloped areas, this may be difficult. Even in developed areas it may be more economic to self-supply. Production systems can start with or build their own mining and processing equipment for materials. They can also start with or build energy sources, such as wind turbines and solar farms.

 Once operating, production generally uses up supplies like lubricants and drill bits, and needs replacements for parts that wear out. These can either be part of the starter set inventory, or supplied from outside as needed. Over time, a growing system can start to make these items for itself. In order to keep growing and improving, a given system has to make or import items faster than old ones wear out. It also needs enough supplies of energy, materials, parts, and other items it can't make.

 We don't expect to reach 100% self-sufficiency. Some items will come from other places, in exchange for surplus products and services supplied to others. We also don't expect fully automated production at current levels of industrial technology. Some people will be needed to use the equipment and do tasks only people can do. Those people can be physically present, or in some cases control equipment remotely.

5.0 - Phase 0: Research and Development (R&D)

 

 The rest of this report describes our program phases and sub-phases in more detail. It does not cover detailed plans and hardware designs both for length and because they haven't been defined yet. We also can't claim this is the best possible program. We present it as a possible path that leverages self-improving production methods. Much more work is needed on this idea, and we invite other people to help. Where next steps have been identified, we note them here, in our two volumes on seed factories and space systems, and our other documents.

 This first R&D phase is numbered zero because it is preparation to make the later phases possible. The sub-phases would be numbered according to the later phases the work applies to. So sub-phase 0.1 would be R&D work that applies to Phase 1: Starter Locations.

R&D Goals

 Our program needs research and development first because we are attempting a new way to organize projects using starter sets and self-improvement. This will need some new equipment and processes for particular environments, especially those in space. So the goal of this phase is to supply ready-to-use technology and designs. Since R&D is the first program phase, it can't evolve from previous ones. Instead it must start with existing items like buildings, tools, machines, design methods, and skills.

 Developing new locations is not the main purpose of this phase, like it is for later ones. Places like offices, industrial space, and test areas will be needed for the R&D work, but can start with existing ones. Testing for unique environments may be easier to do in those environments than building simulators. So some later R&D work may move to difficult locations on Earth, or to locations in space.

Production by R&D Phase

 Despite not being the main goal, some production will happen in the course of setting up R&D locations, testing new equipment designs, and figuring out the best operating flows. But these are secondary to the main goal to provide usable designs and processes for later phases to use.

 Some of the equipment built for testing may be kept and used internally afterwards. This would help expand and upgrade the R&D locations themselves, and serve as a demonstration of the self-improvement process. Other finished equipment, products, and services generated during R&D can get sold or traded to fund further R&D work. Feedback from such items can help improve the designs.

 Final designs should have a long operating life if they are to be useful. So earlier prototypes should last longer than the time needed to test them. Ones with remaining useful lives can be delivered to other locations for later phases and projects. Lastly, the R&D phase may produce some final versions of starter set equipment. These can be used directly in later phases.

Sharing Our Results

 We want our work to have the most benefit for the most people. We plan to open-source the designs, so that anyone can use and improve on them. Individual machines, factories, and the products they produce, would be separately owned, either privately or institutionally.

 The R&D Phase may develop new methods and technology to use for itself in the course of working towards later phase designs. We would also make such new developments available for others to use. An example is full resource accounting, which tracks all the inputs and outputs of a system the way financial accounting tracks money. In order for projects to be functional and sustainable, they should account for everything, including scarce resources and all process wastes. If possible they should be recyclable or usable elsewhere, but you can't do that if you don't identify and track them.

R&D Tasks and Projects

 The R&D work is divided up according to the later phases and projects that need it. Items used by multiple phases are assigned to the first one they are needed for. Later phases start at different times. So the R&D work for each one is started far enough ahead that it is ready when needed.

 New designs and technology are likely needed even for the last phase. So we expect R&D work will continue for the whole life of our program. In addition to internal R&D work, we expect technology to make progress outside our program. So part of the R&D phase is staying current with outside developments so improved designs and methods can be developed later. The growth of locations, and unique conditions found there, may require design updates, new hardware models, and customization. Lastly, we expect feedback from using the items in later phases and suggestions for improvements. All of these are reasons to continue the R&D process.

 The R&D work is also grouped into individual projects according to the technologies being developed or type of end use. So far we have started the Seed Factory Project to develop the basic ideas for self-improving systems, and started working on what is needed for Phase 1 locations and networks.

 Future R&D project examples are ocean mining platforms or interplanetary tugs. Such systems would be used in later phases, so we have not identified specific ones to start yet. There is a lot of science and technology work happening elsewhere in civilization. We do not expect to duplicate that work, but use their results where it makes sense, and contribute back our own results to the general fund of knowledge.

6.0 - Moderate Locations

 

 Once the R&D phase starts providing plans, designs, and technology, the core self-improvement methods stay the same in all later phases. But equipment sets must be adapted to local environments, material and energy resources, and available people and their skills. Finished products and services also need to be adapted for local and export use. So our program concept has multiple later phases to account for all these differences.

 Phases 1 and 2 are for the easiest environment conditions, which we call "Moderate". This includes temperatures, water supply, and a number of others environment conditions. We list them in section 7.1 which covers conditions that are more difficult. Moderate ones are the kinds of places where most people currently live. Among them are locations with significant population and physical development, such as around cities. These locations have enough people, supply sources, and transportation to get started. So they are the easiest ones to build the first projects in. The three phases/sub-phases for these areas are mainly distinguished by scale of operation. They are 1:Starter, 2A: Distributed, and 2B: Industrial.

6.1 - Phase 1: Starter Locations and Network

 

Goals

 The main goals of this phase are (1) provide products and services at the personal and community level, (2) develop experience with starter sets and self-improvement, and (3) develop networks among local sites and different locations. Network members can trade physical items as needed, and coordinate their work on larger or more complicated projects, despite being in different places.

 Networks would be used in all later phases. This is because (1) locations vary in the material and energy sources available. (2) Individuals and groups have variable skills and interests. They also may not want to travel too far to work on projects. (3) Physical space, utilities, safety, and local rules may limit the work done at a particular site.

Starting Points

 Projects in general need tools, resources, energy, and knowledge to complete, or "TREK" for short. Early projects won't have the benefit of a lot of finished R&D work. To start with they can use already developed tools and machines, existing sources of materials and parts, available electric power and fuels, and the many books, online videos, and other information sources on how to do what is needed.

 An early project example is setting up for a hobby or home improvement. Such projects don't have to be completed all at once. They can be started with minimal equipment for the first steps, and gradually add more as skills accumulate. Eventually an owner can start building custom items like a work table or storage for themselves. If they can find other people interested in similar projects they can share knowledge, trade items, and help each other when extra people are needed. Like other parts of our program, people's skills and the equipment they work with are not intended to reach a static end point, but to grow and develop over time. So self-education, training, and practice are encouraged.

 Equipment for this phase starts at the hobby and home use level, for personal and local community products and services. Their duty cycle (percentage of time in operation) is less than full time, and the equipment is smaller and less expensive. This puts the equipment in reach of ordinary people or small groups. Groups of people can afford a number of these smaller items. They can be housed in space they already have, or can build or rent without too much difficulty.

 Equipment may be distributed at people's homes, or grouped into clusters on one property, such as a Community Workshop or small scale production cooperative. Individual sites may be limited in size and cost, but the network as a whole is intended to grow and improve.

Later Improvements

 Improvements can come new R&D work. personal experience, more copies existing items, scaling to larger (and sometimes smaller) sizes, and purchases funded from sales. As the network expands and upgrades itself, it can produce more items internally for further upgrades, and more products for network use or to sell. Network production can be logically grouped into (1) tools and machines intended to make more tools and machines, (2) items intended for production but not for making more equipment, such as a sawmill or greenhouse, and (3) finished products to be used, traded, or sold, like furniture and food.

 The R&D phase would gradually develop plans, designs, and instructions for starter sets, upgrade paths, and custom equipment. These would be shared as information, and can start to be provided as packaged sets. Later projects can then start self-improving faster. A trading network can grow as more sites in more locations are built.

 Examples of future R&D-developed equipment include a 1x2 meter bridge mill, with replaceable heads and bits so it can perform different tasks, and a 15 kW solar furnace with replaceable focus targets. The furnace can directly heat items in a crucible, or generate steam for an electric generator. Such starter set equipment is designed for flexibility, rather than maximum efficiency and speed. That way a smaller starter set can be used for a variety of tasks at lower cost. Later equipment, built with the help of the starter set, can be dedicated to single tasks with higher efficiency and performance. Starter equipment may be supplied finished and ready to operate, as kits with some level of assembly and supplies needed, or purely as plans and instructions.

6.2 - Phase 2A: Distributed Locations

 

Goals

 The goals of this phase are (1) increased scale of sites and locations, and (2) relief from job insecurity and displacement by automation.

Evolution

 Phase 1 locations in general would accumulate skills and equipment. Some sites will move beyond hobby and home use, towards more regular small business and commercial activity. This involves part or full time operation, and selling more products outside the self-improvement network. The larger scale and more intense uses will need different equipment sets.

 When running a business, speed and efficiency become more important, so equipment is chosen or built to do particular tasks well. This results in a larger collection of more specialized equipment. Skills and training also become more specialized and take longer to learn. Particular sites will tend to do a few things well, and trade for other things they need. A comprehensive large node (general purpose workshop or factory) that does many kinds of work is still possible in this phase, but less common. So working sites will tend to be distributed in multiple places.

 Business and commercial scale operation is not limited to production only, but can also serve the full range of habitation, transport, and service industries. For example, a restaurant is a service business, but it needs a building, furniture, and kitchen equipment first. So the logical progression is from core equipment to make more equipment, then finished products like building materials and furniture, and finally industries that don't produce items, but use them to operate.

Ownership

 In the current economic system, separation of ownership and labor results in the problem of job insecurity. The owners of a for-profit business have the incentive to remove workers as soon as possible to save on labor costs. The removal may be due to lower production and sales, or changes in business methods and technology that need less labor or different skills.

 When a person or group has built and expanded their own equipment and business, the owners and workers are the same people. They don't have the same incentive to remove themselves. To the extent they make items for their own use, production would remain constant. If outside sales decrease, they own the equipment to build and start doing something else to make up the difference. Automation is a threat to conventional jobs by needing less labor. But owners who use the same automation for themselves are not threatened with unemployment. Rather they just work less time or more efficiently.

 By diversifying into different industries, self-owned production can integrate with the rest of civilization and be self-supporting. New network members can become owners by first building or buying into a share of core production. They can then use that production to make or trade for what's needed in other industries. Alternately they can start out working for others in their chosen industry, and buy or trade for production shares. Either way they have more security as owners.

6.3 - Phase 2B: Industrial Locations

 

Goals

 The main goal of this phase is to reach the most efficient production capacity by additional growth in scale and specialization. Industrial locations are in the same kind of developed areas and moderate environments as Phase 2A Distributed Locations, so we group them together under Phase 2.

Growth and Specialization

 Industrial nodes can evolve from distributed small business or commercial nodes by continuing self-improvement and growth. They can also be built as new nodes of the final size, where the equipment is supplied by other parts of the network. In that case, supplying the larger equipment and space to house them will likely need outside capital, because individuals or a small group typically won't have enough funds. Gradual evolution from a smaller size by self-production would not require as much, or any, outside funding.

 Larger work spaces with larger input and output flows will tend to limit industrial locations to fewer products. For example, if you are processing scrap metal on an industrial scale into new metal stock, it helps to be near a rail line to transport the scrap and the finished metal. The more products, factory space, and specialized needs you have, the less likely you will find one big location that can satisfy all of them.

 The larger production scale means more outside customers for the products, or larger scale customers. The market area for a site will likely reach beyond a single location, to a region or even world-wide. Since outputs are sold to a wide range of customers at greater distances, transport capacity becomes more important in this phase.

 A narrow product range and large scale markets means demand can be more variable from general economic circumstances or competition. Distributed finance and ownership makes sense in this case. Demand may be low for a particular product, but may be high for something else. In a distributed portfolio these tend to average out. Owners can then reassign their labor and equipment as needed to meet the higher demand products.

 The overall network has a high capacity to recycle and self-produce what it needs. So modifying equipment to meet changing needs is easier to do. This is a somewhat different business model than investors and workers, with managers in between. It more a network of active owner-operators who can change the mix of what they own and what they produce as needed.

 Like distributed locations, industrial ones can serve the full range of industry types. A combination of industrial, distributed, and individual scale industries can meet most of the needs that people have. If they own their own equipment, or shares in them, because they collectively built and grew them themselves, those needs are met securely, despite higher levels of automation.

7.0 - Other Earth Locations

 

Goal

 The main goal of this phase is a better quality of life through sustainable development. The Earth's population is growing, and most people want a better lifestyle. This needs more physical resources and energy. But the Earth is already being stressed by human impact on the environment, and future growth will only increase the stress.

Method

 One way out of this dilemma is to produce abundant renewable energy with self-improving systems. These systems make more of themselves exponentially, including more power sources. Renewable energy will have much less impact on the planet's heat balance. Large amounts of energy allow increased reprocessing of wastes, and extraction from lower grade ores or even common rock and ocean water. Rapid expansion brings material goods to the rest of the world faster. Self-production and automation lowers the relative costs of products, energy, and materials.

New Locations

 Increased supply of raw materials and energy will likely need access to more difficult and remote locations. So Phase 3 covers working in areas that are thinly or completely uninhabited, or that have difficult or extreme local environments. New designs and processes will be needed for such areas. So a new program phase with added R&D is started.

 Harder conditions are a matter of degree, rather than absolutes with a clear dividing line. Sections 7.1 and 7.2 list the ones we have identified. We define the "normal" (moderate) range as those where the middle 90% of of people live. Difficult and extreme conditions are then significantly above or below the moderate range.

 If at least one of the eleven parameters is well beyond the moderate range, then the location is assigned to the difficult category. Extreme locations are even farther from moderate, and can be hostile to people living and working there. More remote-control and automated operations will tend to be used, instead of trying to build controlled environments for people.

 We want to preserve the Earth's total environment, and the parts that are still in a natural state. So developing the difficult and extreme locations must consider sustainability, renewable energy, and environmental impact. An example would be building offshore fisheries to replace wild fish catches. The latter are putting a strain on the ocean food chain, so it is desirable to minimize that impact. But the fisheries must consider all their inputs and outputs in a total system approach to avoid unintended side-effects.

 The mechanics of building in these locations is somewhat different than previous phases. These areas are less populated, with fewer supply sources and utilities available. So growing from a minimal set of tools and machines is harder to do. Instead, more finished equipment is sent from previous locations to start basic functions like mining and producing energy. A set of production equipment then uses these resources, plus some level of imported supplies, to increase capacity.

 That capacity then supplies products and services are for local use. Surplus output is traded with the rest of civilization to make the locations self-supporting economically. Once built up, a location can also contribute to starting additional ones. The experience gained in working in difficult or extreme conditions, working remotely, and building up resource extraction and production in such places will be useful for later phases beyond Earth.

7.1 - Phase 3A: Difficult Earth Locations

 

 We define moderate conditions as those where the middle 90% of the Earth's population lives, with 5% at the upper or lower ends for a given parameter. This definition is somewhat arbitrary, but we think reasonable from a design standpoint. The "Difficult" environments are then those that are at least 10% beyond the moderate range in at least one parameter. 10% is measured either linearly or as a logarithmic factor, depending how wide the normal range is. The parameters and moderate and difficult ranges are:

 Temperature - This is measured by winter average daily lows and summer average daily highs. The moderate range is 260-310K (-13 to 37C). A given location is likely to exceed either the high or low limit, but not both. The difficult range is therefore below 255K (-18C) or above 315K (42C). Examples of difficult temperatures include Chelyabinsk, Russia, where average winter lows are -19C, and Death Valley, California, where summer highs are up to 47C. The lower limit ie more likely to be reached at high altitudes and latitudes. The high limit is more likely to be reached deep underground, because the Earth's internal temperature rises 25 Kelvin/Celsius on average per kilometer of depth.

 Water Supply - This is measured by fresh water supply in meters or tons/m^2 per year from rain, rivers, snow, ice, moisture condensation and freshwater aquifers. Salty surface water and aquifers are not included, as they aren't drinkable without desalination. Aquifers are limited to natural replenishment rates, as they are not sustainable if drawn from faster. The moderate range is 0.25 to 2.5 meters/year. Since this is a large range, we use a logarithmic scale, and define difficult as 26% below or above the moderate limits, or <0.185 and >3.15 meters/year. The world's drier deserts fall below the 18.5 cm rainfall level, and places like the east coast of Nicaragua exceed the 315 cm upper limit on rainfall. Too much water is difficult because it can cause problems like flooding, erosion, and decay.

 Atmosphere Pressure - This is measured by average local air pressure in kiloPascals (kPa). For reference, standard sea-level pressure is 101.325 kPa (14.696 psi). The moderate range is assumed to be from 80-100 kPa (near sea-level to 2000 meters altitude) Difficult pressures are below 70kPa (2750 meters altitude) or above 110 kPa (750 meters below sea-level). These correspond to high mountains or plateaus, and deep underground at low altitudes, since the lowest surface elevation is -413 meters. Low pressures and rapid changes in pressure can cause medical problems for people, so pressure-control is needed where people are. Effects on equipment are mostly minor in this range.

 Ground Pressure - This is the ground/soil strength at the surface, or surrounding water or rock pressure below the surface, in MegaPascals (MPa). These affect the design of structures, and values that are too low or too high become difficult. For reference, average household floors are designed for 0.275 MPa loads. The moderate range is 0.25 to 2.0 MPa. Difficult conditions are then below 0.19 MPa or above 2.5 MPa. The high limit is reached at ocean depths of 250 meters, and underground at depths of 100 meters in average rock. High surrounding pressures require closed containers to lower them for people, or support structures to prevent collapse. The low limit is reached in open waters (zero strength), fine sand or moist clay (low strengths). Low ground strength requires larger building foundations, or floating construction in the case of open waters

 Energy Supply - This is measured by average energy supply from renewable natural sources in W/m^2. Wind and solar are available in most places, and are rapidly renewable. Ocean thermal and geothermal are widely available if you go deep enough, but take long periods to renew once depleted, so we only count their renewal rate, not the stored energy. Sources like hydroelectric or tidal energy are not available everywhere, but counted if they are.

 Fossil fuels are not sustainable because of finite supply and the waste products they produce. Biofuels may be produced sustainably. Fuels for nuclear fission and fusion (which is still being developed) are in large enough supply to be considered sustainable but require mining or separation. They can be used to produce energy, but we don't count their contribution to local supply.

 Low energy supply is difficult because some is needed for almost every kind of human activity. If it is not available locally, it must be imported by methods like fuel delivery or power lines. High levels of energy supply are not considered difficult. The range of energy flux is roughly 150 to 900 W/m^2 on Earth, so a difficult low value is 125 W/m^2. Any significant depth below the surface is cut off from wind and solar sources, so are likely to be difficult and require energy supplied from elsewhere.

 Gravity Level - This is mainly one of the conditions for space environments. On and near the Earth's surface it does not vary by more than 10% unless you are in a centrifuge or accelerating vehicle, so there are no natural places on Earth beyond moderate conditions. Low gravity causes biological problems for people, and may for animals and plants. High gravity is difficult to work in for people, and requires extra structural support for physical items.

 Radiation Dose - This is measured by unprotected background radiation in milliSeivert (mSv)/year. Industrial exposure, such as to medical imaging staff, or from mining, using, and disposing of radioactive materials, is not considered an environment condition. But such exposure needs its own designs for safety and shielding. Natural background radiation varies by location, according to altitude, magnetic field, and what materials are in the ground below. In most places on Earth it varies from 1 to 13 mSv/year.

 A few places have high radiation levels from concentrations of radioactive elements and their decay products, up to 135 mSv/yr. People have lived in such locations for many generations, with no apparent ill effects. Since adaption may have occurred for long-term residents, we will be conservative and consider high radiation levels a hazard to the general population.

 Levels above 17 mSv/year would be considered difficult. Depending on sources, they might require shielding, sealing, or air circulation. Low radiation levels are not considered hazardous, so background levels below 1 mSv/year are not considered difficult. Note that the human body contains some radioactive elements naturally, so there is no zero background level. Even the highest natural radiation levels on Earth are not significant for most equipment designs.

 Ping Time - This is the round-trip communication delay to the next nearest 5% of world population, in milliseconds (ms). Long delays create difficulty in voice communications or real-time remote control, and slow down any computer network-based activity. There is no lower limit for this parameter, since short ping times are not a difficult condition.

 On or near the Earth's surface we consider ping times above 100 milliseconds to be difficult, as this much delay starts to be noticeable to people. There are few locations that have such high values to reach 5% of the world's people. The 5% value is because you can choose to do tasks like remote control from reasonably nearby, and not from the farthest place on Earth. This parameter becomes more important in space. The speed of light limits operations to within 15,000 km to stay under 100 ms. That only reaches moderately high Earth orbit, and most of space is far beyond that distance.

 Travel Time - This is the maximum one-way normal travel time for people, to reach the nearest 5% of other people. Travel time for cargo is assumed to be proportional to that for people. High travel times makes it more difficult and expensive to bring in people with special skills, or necessary parts and materials. Densely populated areas can usually be reached in 5 hours or less. Most of the world's populated areas can be reached within 48 hours, so we set this as the upper limit for moderate (developed) travel. The worst case travel time is 10-20 days for parts of Tibet which lack roads, and ocean locations distant from any airports, requiring ship travel to reach. Very low travel times are not a difficulty, so we set no lower limit for this parameter. We define difficult travel as needing more than 2.5 days.

 Stay Time - This is the average stay time per person per location, in years. People stay in the same location if they live and sleep there the majority of the time, and make trips to other locations less than half the time. Short stay times are more difficult because of increased transportation needs and staff turnover. The short times may be caused by a harsh environment, lack of habitation and services, or the location is simply undesirable. It can also be caused by a rapidly growing population lowering the average residence time. In that case, the difficulty is caused by having to rapidly build new habitation and services.

 Long stay times are not considered difficult, and their upper limit is the human lifespan. Rapidly growing areas provide the shortest average times on Earth, 7 years if normal turnover is added to growth. Since the upper bound is ~70 years, we will set the difficult limit at 25% below the shortest average, at 5 years. Examples where such low values occur are mining and construction camps in remote locations.

 Transport Energy - This is the total energy to reach a location from the nearest 5% of population, by the most efficient method, in MegaJoules per kilogram (MJ/kg). For reference, 3.6 MJ = 1 kiloWatt-hour of electricity. Transport energy includes kinetic, potential, and frictional energy. High transport energy is difficult because of increased need for equipment, and their higher cost of operation.

 On Earth, potential and kinetic energy of transport are generally low, and friction dominates. Rail and water transport are currently the most efficient bulk methods, and range from 0.225 to 2.25 MJ/kg between densely and sparsely populated areas. Low transport energy is not considered difficult, but we set values above 2.85 MJ/kg to be. Such values can occur when rail and water transport are not available, and part of the trip must be by less efficient methods. It can also happen when there is a lot of altitude change on the route, increasing frictional losses so as not to exceed speed limits.

 Some of these parameters change with time, due to technology and development. For example, parts of Alaska had long travel times when the only available transport was by dog sled. Once small airplanes and a network of landing fields were available, it became less difficult. It may be a specific goal to upgrade a location to less difficult status, but we define it for phases and R&D by the pre-existing conditions that have to be dealt with.

7.2 - Phase 3B: Extreme Earth Locations

 

 We define extreme locations as an additional 10% beyond the difficult range. This is again in linear or logarithmic amounts, depending on the span of moderate conditions most people live in. The more extreme parameters will need further design modifications, and therefore supporting R&D to develop them. We define no upper bound on how extreme things can get, they are only limited by the natural environment and general state of civilization. The parameter values are:

 Temperature - average daily lows below 250K (-23C) or average daily highs above 320K (47C). The lows might be found in Antarctica or at high altitudes. The highs are found deep underground or in the hottest deserts.

 Water Supply - The lower range is less than 0.12 meters/year (4.75 inches), which is a very dry desert. The upper range is more than 3.8 meters/year, which is found in the wettest rain forests.

 Atmosphere Pressure - The extreme ranges are below 60 kPa or above 120 kPa, which correspond to altitudes above about 5500 meters or below -1600 meters. These correspond to very high mountain tops and deep underground.

 Ground Pressure - The ranges are below 0.12 MPa or above 3 MPa. These correspond to soft clay or open water at the low end, and depths of 300 meters in water and 120 meters in rock.

 Energy Supply - The low range is below 90 W/m^2 from wind and solar, which is mainly encountered below the surface. High values of energy supply are not a difficulty.

 Gravity Level - This parameter does not vary by more than a few percent on Earth, so extreme conditions more than 20% beyond normal do not occur.

 Radiation Dose - The extreme range is more than 21 mSV/year, which occurs in some natural high radiation areas, or if spending a lot of time (>25%) at high altitude near the magnetic poles, where cosmic radiation can come down vertically.

 Ping Time - The range for extreme ping time is more than 125 ms round trip. This is nearly around the world at the speed of light, so accessing 5% of the population only takes this long if radio or fiber communications routes are very indirect or unavailable.

 Travel Time - The range for extreme travel time is more than 3 days to reach. This is found only in very remote areas without conventional transportation.

 Stay Time - The lower range is average stay times below 3 years 4 months, which mainly would be found in temporary work locations.

 Transport Energy - The upper range for extreme transport energy is above 3.5 MJ/kg. This is reached mainly when inefficient transportation has to be used.

8.0 - Phase 4: Orbital Locations

 

Figure 8.0-1 - 1952 space station concept by Wernher von Braun and Chesley Bonestell.

Goals

 The main goals of the later phases are using space to bring benefits to Earth, and to help with some long-term problems that can't be handled any other way.

 Figure 8.0-1 is an early concept for a rotating space station, made 5 years before the first orbital launch of Sputnik 1. Note the ring-shaped solar collector on top. This would heat a fluid to produce power, since solar cells were not well developed at the time. We show it as a reminder that plans can only be made from what is known at the time. Our approach to developing space may look equally out of date 70 years in the future. Despite that, we have to start somewhere and then make updates as needed.

Approach

 Sections 8, 9, and 10 cover Phases 4, 5, and 6 in that order. Sub-phases for each are grouped together because they involve working in similar space environments. Orbital locations (Phase 4) come first, because Earth orbit has to be reached before going anywhere else in space. Planetary system locations (Phase 5) share being on or tied by gravity to the larger Solar System bodies other than Earth. Their gravity wells take more work to travel to and from. The local environments are also different on and around these bodies.

 We expect the various sub-phases to have different starting times, but overlap and continue in parallel once started. Phase 6 (Interstellar) involves places beyond the Sun's gravitational dominance. It is expected to be last in time. It is hard to predict what technology will be available by then, and how such distant locations would be used. So the last phase is mainly included as a placeholder and to provide some direction for future work.

Current and Near-Term Space Industry

 Working on long-term problems doesn't have an immediate economic return. So the first uses of our approach for places beyond Earth would be to support existing and near-term space industry. According to UN records there were over 8200 satellites orbiting the Earth at the start of 2022. Of these, about 4850 were active. There are a smaller number of spacecraft and other items that have been sent to the Moon and beyond, some of which are still operating. The inactive equipment, plus other discarded items and fragments, make up artificial Space Debris. The increasing amount of debris is one of the long-term problems that need solving.

 Total Economic Activity related to space was $386 billion as of 2021, split between government and private projects. But nearly all of the people involved, and most of the physical tasks, happen on Earth. This provides a starting point for using our self-improvement methods and other advanced technology. In turn that should lower costs.

 Reaching space is generally industrial-scale activity. Rockets themselves are large, and so are the places and equipment to build and launch them. So it would be part of or follow Phase 2B's other industrial locations. What is sent to space can be as small as hobby scale. Amateur Radio Operators have sent satellites into orbit, and well over a thousand Cubesats based on 10 cm modular sizes have been sent to space. Building and operating equipment sent to space more typically ranges from Phase 2A's small business and commercial scale up to the industrial level.

 Reaching space was very expensive until recently because some or all of a rocket was discarded after one use. The high cost limited space activity to large nations or groups of them at first. Over time, commercial space activity has grown to be about 75% of the total. Lower cost transportation and satellite equipment is actively being pursued. The methods include adopting mass production, and discarding less or none of the rocket each flight.

 Most equipment sent to space is also discarded when it fails or reaches the end of its useful life. This adds to the cost of operating in space. Refueling, maintenance, and repair of equipment in space is very limited. New production, upgrades, and recycling is limited to non-existent. Total cost can be lowered by changing how space projects are built, delivered, and operated. In turn this would expand existing uses, and open up new ones like private space stations and space tourism.

Long-Term Sustainability

 As of 2021 fossil fuels supplied about 77% of global primary energy. Since about 1900 their rapid growth powered most of the development of modern civilization. But that comes with a number of unfortunate side effects. They include environmental damage, pollution, and adding greenhouse gases, mainly CO2, to the atmosphere far faster then natural processes remove it.

 These gases reduce infrared radiation back to space, altering the balance between incoming sunlight and outgoing heat. Venus' surface temperature of 462 C (864 F) shows why this is a bad idea. Only 50C of Venus' higher temperature is due to being closer to the Sun. The rest is primarily heat trapped by a thick CO2 atmosphere. Society must transition this century to renewable non-carbon energy sources, so Earth doesn't become more like the hell that Venus is.

 Despite the large-scale use of fossil and other energy sources, current civilization can't afford to capture and reprocess all waste materials, nor extract new materials from abundant low-grade sources. New materials come from Ores instead. These have higher concentrations of desired products, which take less work to extract. However, high-grade ores are in limited supply. If used materials are not fully reprocessed, those ores will eventually run out. So the current state of civilization is unsustainable. It is heading towards severe problems from increasing temperature, running out of affordable materials, or both.

 At the same time, the world's population is growing, and not everyone has the benefits of full development. Such development demands even more energy and materials. It's unfair to deny these benefits to some people because others were the first to get them. A growing population with a high standard of living will put more stress on the remaining natural world, and deplete accessible resources faster. Self-improving factories and other advanced technologies can be used to build more renewable energy sources and reprocess more wastes. This would have less impact on Earth, but it does not reduce it to zero.

Civilization-Level Risks

 Another problem is preserving civilization and the biosphere in the face of large-scale risks. One such risk is runaway greenhouse warming due to positive feedback loops. This is different than the temperature rising a certain number of degrees from higher CO₂ levels. Melting ice caps can expose darker water or land, increasing the absorbed sunlight and causing further melting. Another feedback loop is release of methane from frozen ocean hydrates and organic matter in permafrost. Methane is a strong greenhouse gas, and so can lead to accelerated release.

 Another risk is from asteroids. Large asteroids fly past Earth fairly frequently, and occasionally hit it, causing widespread damage. There are enough craters, recorded impacts, and near misses to know it is a low probability event, but can be catastrophic if it does. So it is worth trying to reduce the risks. Note that small objects either burn up in the atmosphere or only cause local damage, and don't require civilization-level action to prevent.

 There are other large-scale risks besides these two. Examples include Supervolcano eruptions, genetically engineered plagues, and nuclear war. It is worth some effort to identify these risks, and reduce them if possible. Backup locations beyond Earth can be a last resort if such efforts fail, but most efforts should likely be directed at prevention rather than recovery.

8.1 - Using Space to Solve Earth's Problems

 

 There are abundant energy and material resources in space. If the cost of using them can be brought low enough, then that becomes preferable to, for example, putting more solar panels in climates unsuited to them, or digging ever deeper underground to find high quality ores.

 There is seven times more solar energy available in space near the Earth than the average on the ground. Atmospheric absorption, night, and weather account for the difference. The equipment to collect that energy is also about seven times lighter because it doesn't need to handle gravity and weather. So the energy to equipment mass ratio is roughly 50 times higher.

 There is also a wide variety of accessible materials in space, starting with the Moon's surface and nearby asteroids. These have been "pre-mined" in the sense that impacts have left them broken up and loose. Extracting them doesn't need heavy equipment, so the tons mined per ton of equipment is high. The combination of high energy and low equipment could allow rapid bootstrapping of space industry. The products can then help solve the problems and risks we noted above.

Lowering Space Operations Cost

 Reaching and working in space has been very expensive, especially beyond the lowest Earth orbits. But that is an engineering problem, not one set by basic physics. For example, wholesale potatoes are on the order of $300/ton, and the wholesale electrical energy to put those potatoes in Earth orbit (8.7 MWh) is on the order of $550, less than twice as much. Sending even cheap bulk commodities to space would be affordable if done with high efficiency. Current launch costs are quoted at $1.52 million/ton or more (Falcon Heavy, 2022), 2750 times as much. This shows how much room there is for improvement.

 There are a number of ways this cost can be reduced. Reaching space today requires a good deal of equipment on Earth, like rocket factories, the rockets themselves, and launch sites for them. Self-improving automated production can lower the costs of these. As with other industries, you can begin with a starter set, and grow it until you have mature factories that produce the space hardware you need.

 A large amount of rocket and satellite hardware is discarded after use. This is a major contributor to high costs. Improved designs can allow reuse and repair. Conventional rockets are also inefficient. They require about 40 times the payload mass in fuel (for LOX/RP-1) containing 387 MJ/kg of fuel energy. The payload ends up with 32 MJ/kg of kinetic and potential energy, so the fuel efficiency is only 8.3%. Alternate launch methods can dramatically improve on this value, but there has to be enough traffic to space to justify their development.

 Advanced production methods in space, using materials and energy already there, can ultimately reduce mass launched from Earth by 98-99%. The transportation component of operating in space can then be reduced by a similar ratio. If in-space production costs are less than the launch savings, then overall costs go down.

 More efficient space technologies, like electric propulsion and closed life support, further reduce the mass from Earth needed to operate. The closer we can source supplies to the desired destination, the less effort is needed to move them there. So a Lunar or Mars base would ideally get most of what it needs locally, or from not too far away, and only get from Earth what can't be found or made otherwise. The combination of all these methods would get much closer to "potato cost".

Space Development Process

 Our approach would follow the same general path in space as it does on Earth. In particular the methods used for difficult and extreme locations on Earth are relevant, although the details will differ. Space is nearly undeveloped and barely populated. So early tasks include delivering equipment to supply energy and gather raw materials. A core set of processing equipment would be used to turn raw materials into basic supplies like propellants, and production inventory like metal stock.

 Other equipment takes these products, plus some amount of imported items, and fabricates parts for more production equipment, plus finished items like habitats for people and food production. Metals for machinery and construction are likely the majority of first generation production, since that is the foundation of industry on Earth. Second and later generation equipment can then produce other materials and products in an expanding sequence.

 In the early stages there is less equipment available at a given location. So a larger percentage of parts and materials has to be imported from previous places, or from Earth. As more equipment accumulates, a higher percentage can be produced locally. Once a given location has matured enough, it can start to make items for new starter sets. These can be used in the same region, such as other parts of the Moon, or sent off to start developing new regions.

 Once a location can export a surplus of locally made items, they can be traded for those it can't make, or needed materials that are locally rare. Such trade would be based on Comparative Advantage like it is on Earth. By export and trade a location can become economically self-supporting, and not a cost burden. This is in contrast to a station or base that can't make things locally, which has to be supplied from elsewhere at a continuing cost.

 Self-supporting locations can produce an expanding wave of civilization and life as far as people want to carry them - throughout the Solar System, and in the long term, beyond it.

General Space Environment Features

 Orbital locations in Phase 4 begin at 200 km altitude above the Earth's surface, where atmospheric density is low enough for stable orbits. They extend beyond that to the limits of stable orbits bound by gravity to Earth, then to interplanetary orbits at all distances from the Sun. The planetary system locations of Phase 5 are embedded within the larger interplanetary region, and move with the major bodies and the gravity fields they produce.

 The environment conditions, raw materials, and available energy vary widely across the different regions. So we divide Phase 4 into six sub-phases by region, and Phase 5 into five sub-phases. We expect their development to start mostly in order by distance from Earth. Orbital locations include smaller bodies like asteroids found there, and planetary systems include an area of stable orbits around them and the smaller bodies tied to them by gravity.

 The environment parameters for Phases 4 and 5 are generally more difficult than extreme ones on Earth (Phase 3B). The added difficulty in many cases is incremental, not orders of magnitude steps, and not in all parameters. Proper design and operation can deal with most of these conditions, but some places are so extreme that current technology has no way to handle them. The general ranges are noted here. Some details for sub-phases and particular locations are noted below. Extensive and growing knowledge about them comes from the field of Planetary Science.

• Temperature - Distance from the Sun, and the percent field of view of the Cosmic Background, which is at near absolute zero temperature (2.7K) are the main determinants of local temperature. It can range anywhere from above 700K to below 50K (+425 to -225 C). Partly shadowed orbits, or night on a surface, can produce wide temperature swings. Reflection from the surface of a body, or underground surroundings, will modify the ambient temperature.

• Water Supply - Orbital locations don't have a weather system that delivers a renewable water supply like Earth. But some bodies have water in the form of hydrated minerals or ice. Liquid water layers may exist inside dwarf planets and moons, and water in general is abundant beyond the "frost line" around 3 AU, where temperatures are low enough for ice to be stable in a vacuum.

• Atmosphere Pressure - Vacuum is the normal condition in open space and on the surface of most bodies. Some of the larger dwarf planets and moons have non-zero pressures, and all the major planets except Mercury have significant to dominant atmospheres.

• Ground Pressure - This doesn't exist in open space, and is generally low even for larger asteroids, either because of low gravity or low surface strength. Ground pressure can become significant if you go deep enough into larger asteroids. It becomes very high inside large moons and major planets.

• Energy Supply - Varies from above 10 kW/m² in close solar orbits to below 1.5 W/m² beyond Neptune. Orbits with time in shadow lose a percentage of this. Surfaces in vacuum reduce solar energy by about 50% from nights, with variations from topography like mountains and craters. Atmospheres can further reduce solar energy.

 Other sources like wind, precipitation, and geothermal may be available on some bodies. Nuclear power is possible using fuel delivered from Earth or mined from places with radioactive elements like the Moon. Power can be transmitted over moderate distances using conductors and beams, or even simple reflectors.

• Gravity Level - Natural gravity ranges from zero in free orbits, to about 3% of Earth's on dwarf planets, and up to 2.4 times Earth on larger moons and major planets. Artificial gravity can be supplied by rotation where biology or industrial processes need it. Artificial gravity is only limited by structural materials and practical issues like arrival and departure.

• Radiation Dose - Most orbits and surface regions have high natural levels of radiation from galactic cosmic rays, solar particle events (flares), and Radiation Belts like the ones around Earth. Devices like solar panels and electronics are generally less sensitive to radiation than living things, but can still be damaged or temporarily upset.

 Radiation can be lowered to safe levels using bulk mass as shielding, or possibly artificial methods like magnetic fields. Shielding mass in orbital locations can come from asteroids or imported from moons. On substantial bodies their mass provides partial natural shielding, and going underground and arranging local materials can provide the rest. Transport vehicles can use fuel, water, or other supplies as shielding. Large habitats may get enough shielding from their outer structure, equipment, and storage tanks.

• Ping Time - Round trip communication time varies greatly from milliseconds in low Earth orbits to hours or even days in the outer Solar System. Essentially all the communication time is due to speed of light delays. On Earth, fiber-optic cables transmit at about 2/3 the speed of light, and follow indirect paths from geography and a spherical planet.

• Travel Time - This also varies greatly according to orbit region. It can take a few hours to reach low Earth orbit or return from it to the ground, plus some travel time to other population on the Earth's surface. Travel to the outer Solar System using known propulsion systems will take a number of years or even decades.

• Stay Time - This is currently very short because there are no permanently inhabited locations in orbit. Astronaut crews typically stay about 6 months aboard the International Space Station. With the development of larger, more permanent locations, with artificial gravity, food supplies, etc. the stay times can increase to a number of years.

• Transport Energy - Much less than 5% of civilization is in space, so transport energy is measured from the Earth's surface to an orbital location. This is a minimum of 33 MJ/kg, set by the physics of reaching low Earth orbit. It is a lot higher using current rockets, because their operating efficiency is low. More distant orbital locations require additional energy to reach, and currently this reduces cargo mass dramatically, producing even higher transport energy/kg.

8.2 - Phase 4A: Low Orbit Locations

 

 Sections 8.2 to 8.7 cover sub-phases 4A to 4F. We limit the a amount of detail to keep the size of this report reasonable, and in some cases is limited by the current state of knowledge about the regions. Each region would be developed using the general approach in Section 8.1, with some methods adapted to local conditions. The start of each successive sub-phase is staggered in time, but a region does not have to be fully developed before starting on the next one. They would develop in parallel once started.

 We suggest some economic uses for these regions, how to reach them, and how to develop them. We don't know enough to say if these are the best or only uses for them, and we certainly don't know what ideas other people will come up with in the future. So consider this report as a starting point for others to improve upon.

Low Orbit Features

 Earth orbits form a continuous range from 200 km, the minimum set by atmospheric drag, to the maximum set by Sun's gravity becoming dominant. We divide that range in half by the transport energy required to reach it, at 2700 km average altitude. Conditions are different enough between low and high orbits to get their own sub-phases. Orbits can be elliptical and constantly vary in altitude, so we use the average between the high and low points, which is called the Semi-Major Axis.

 Objects in low orbits are in the Earth's shadow about 22-40% of the time, reduceing available energy. The Earth fills a large part of the field of view, which affects thermal balances, and lighting when over the sunlit side. Orbit periods are 2.5 hours or less, so travel time from the Earth's surface is fairly short. Ping time by way of ground stations is under 20 ms, so not difficult. But low orbits have a limited view of the Earth's surface at one time. So multiple ground stations are needed, or communications are relayed by a higher satellite. This can add up to 500 ms to round-trip communications, which is a noticeable delay.

 The Earth's magnetic field traps particles into Radiation Belts that begin at low orbits and extend past them to high orbits. Unprotected people and electronics can be damaged by the high radiation levels. So spacecraft have to be designed to withstand radiation, avoid these belts, cross them quickly, have sufficient shielding, or the belts depleted artificially.

 Material resources are relatively scarce in low orbit. They include the upper edge of the Earth's atmosphere, and debris from inactive satellites and rocket stages. The mass of particles in the radiation belts is very small. Other materials have to be imported from Earth or higher locations.

Economic Uses

 We would like all regions in space to become economically self-supporting. Earth orbits already are, with 75% of total space activity being commercial. Low orbits are occupied by a large number of active satellites serving the people below. Current uses include Earth observation, such as weather, mapping, and agricultural monitoring. Many satellites are now used for communications relay between points on the surface. Government uses include research, such as the Space Station and Hubble Telescope, and national security.

 Future uses may include tourism, orbital assembly and maintenance, and payload transfer, and refueling for more distant destinations. Further development of low orbits would start with existing markets. It would expand to new ones as transportation costs are reduced and local industry built up. We discuss some options in this section, but it is an area with projects being worked on by many others.

 We don't expect large-scale production and habitats in low orbits, because more materials and energy are available higher up. We do expect low orbits to become transit points, because below the radiation belts is the nearest place to Earth that is reasonably safe and doesn't need constant propulsion to maintain position.

Transport from Earth

 Low orbit has few available materials, so most items have to be imported. Rockets and space hardware have existed for decades, but they are still too expensive for many future uses. As noted in section 8.1, self-improving and automated production can help lower the cost of building and running aerospace factories and launch sites.

 Reusing rocket hardware can improve costs substantially, but conventional rockets have low energy efficiency. They are limited by the energy in chemical Propellants and the mass of the Earth, neither of which is changing. A shift to different launch technologies can can improve efficiency and cost. But there has to be enough traffic to justify the added R&D cost in the face of existing rocket systems. There are many possible launch technologies. See Part 2 of our volume on Space Systems Engineering for an extensive list. We provide one example here to illustrate the possibilities.

Figure 8.2-1 - AEDC Range-G Hypersonic Research Gun (on left, 20cm interior diameter of barrel).

 Hypersonic Guns - Hypervelocity gas guns have been used in research for decades (Figure 8.2-1). They are inexpensive to build compared to most aerospace hardware. This is because they don't have to fly, so can be made of heavy industrial parts, and Light Gas Guns are basically simple devices.

 A larger version of such a gun, on a mountain with the correct slope, can supply 50-70% of orbit velocity for bulk cargo which is not sensitive to high g-forces. These include fuel, water, structural parts, even frozen food. Outdoor barrels measured in km rather than meters lower g-forces and operating pressures. But they are still generally too high for delicate cargo and people. Those would use other kinds of transportation. Industrial factories grown from starter sets could be a low-cost source for the construction equipment to build on the mountain, the high pressure pipe, other parts for the gun, and an energy source to compress and heat the gas for launch.

 Muzzle velocities much higher than ~4 km/s (half of orbit speed) become increasingly less efficient. This is because of limits on expansion rate of the working gas, and increased drag and heating while climbing through the atmosphere. The remaining part of reaching orbit is supplied by an internal rocket engine on the projectile or by other methods. Because the rocket engine only supplies half or less of the velocity, it is many times smaller relative to cargo than conventional rockets.

 The fuel-to-payload energy efficiency is roughly two-thirds, much better than conventional rockets. The gun also uses energy, but it is relatively cheap to operate. It is stationary on the ground, uses inexpensive materials, and can be used many times. The projectiles are rugged and durable, and can also be used many times. Re-entry is much gentler than the initial launch. The operating cost per ton to orbit should therefore be lower than conventional rockets. A gun-type launcher could deliver a large portion of the mass to orbit. There is no requirement that everything going to space has to travel the same way, any more than it does here on Earth.

 Other Launch Methods - Hypervelocity guns are just one example. Other technologies with reasonable prospects include high-speed air-breathing engines for the early part of flight, and orbiting structures with suborbital landing platforms for the later part. Both are more efficient than chemical rockets in their respective velocity ranges. Unfortunately neither can easily serve the whole job of transport to orbit. A combination of systems, each operating where it works best, is likely the better option.

 High speed jet engines and orbital platforms would require substantial R&D, and are therefore not likely to be the first things built. Instead, lowering the cost of conventional rockets is the first step. It would then be supplemented with a low R&D system like a hypersonic gun. Once new markets are opened up by the lower costs, the more advanced technologies that need more R&D can then make economic sense.

Mining and Production

 Low orbits are not ideal places to process raw materials. That requires a lot of energy, and sunlight is blocked a good percentage of the time. But there is enough energy to fabricate parts and assemble them to finished items. For example, spools of high strength fiber and metal wire are rugged enough to be launched by bulk systems. The fiber and wire can be wrapped and plasma-sprayed in layers around inflatable or collapsible forms, to build up large, lightweight structures. Large pressurized volumes built this way can then house other production and assembly equipment and people to work there.

 There are some material resources in low orbit that don't require a lot of processing. At altitudes of around 200 km it may be possible to "scoop mine" the upper atmosphere. A collection scoop funnels incoming air, which is very thin at this altitude, to a vacuum pump and compressor. A portion of the air is expelled by electric engines at much higher velocity than the incoming flow. This makes up for drag from the scoop. The remaining air is stored in tanks.

 When the tanks are full, the mining ship climbs higher and unloads to storage tanks at a depot. The reason to mine like this, rather than launching gases directly from Earth, is the solar arrays that power the mining ship can produce 1000 times the energy needed to put themselves in orbit over their operating life. As long as the gas mining can be done with reasonable efficiency, launching solar arrays rather than tanks of gases results in much more usable product in the end.

 A steady supply of air (or nitrogen and oxygen if separated) obviously can be used to support people in orbit. It can also fuel tugs that collect dead satellites and debris from the Earth's "debris belt". This both reduces the hazard they create, and supplies useful resources. The collected materials can be scavenged for usable parts or recycled into new products. Dead satellites and empty rocket stages are made of aerospace materials, so they should not need a lot of processing to reuse.

 Mining the debris is only feasible with a cheap source of propellant and efficient electric engines. The pieces are in random orbits, and would consume too much propellant to gather otherwise. Air plus debris mining can provide enough materials to support some production in low orbit. The larger sources available from the Moon and asteroids, and the full-time solar energy in higher orbits, leads to the majority of production being done elsewhere. It can be efficiently delivered "downhill" using gentle Aerobraking. Low orbit mining and production then ends up supporting local uses, and this region functions as a transfer point between the ground and elsewhere.

8.3 - Phase 4B: High Orbit Locations

 

High Orbit Features

 We define high orbits as extending from 2700 km average altitude to the limit of the Earth's dominant gravitational influence, or Hill Sphere. For Earth this is about 1.5 million km, but towards the outer edges orbits become less stable. This is a large range of distances, but it only represents the upper 25% of energy between the Earth's surface and escape. That's because gravity is an inverse square force and weakens rapidly as you increase distance.

 The Moon is the most prominent feature in high orbit. It has its own area of dominant gravity, with a radius of about 60,000 km, and reasonably stable orbits with semi-major axes to about 35,000 km. Additional energy is needed to descend through the Moon's gravity field to low orbits or the surface. Conditions are also different enough near and on the Moon that we assign the region within 35,000 km to Phase 5A - Lunar Locations.

 High orbits are in sunlight 85-100% of the time, reaching the highest values when farther from the Earth and Moon. Temperature is determined mostly by the Sun and the cold Cosmic Background, but at lower altitudes the Earth contributes a significant amount of reflected light and infrared heat. Orbit periods range from 2.5 hours to 7 months, so travel times by the most efficient routes can be long. Direct paths can be much faster, 12 days or less, at the expense of additional energy.

 Ping time varies from as little as 25 ms, which is not difficult, up to 10 seconds, which has a large impact on voice, real-time control, and electronic data. The upper part of the Earth's radiation belts, solar, and cosmic radiation create high to dangerous levels for people and equipment. Energy resources are abundant in this region, but material resources are low in their natural state. The Moon and Near Earth Objects can supply materials with fairly low transport energies.

Economic Uses

 One orbit in this region, geosynchronous, at 35,000 km altitude, is already heavily used. This orbit has a period of 24 hours, which matches the Earth's rotation. So satellites appear to stay above a fixed ground location, and ground antennas can be stationary rather than having to track satellite motion. Synchronous orbit is in the outer fringe of the radiation belts.

 Future production and human habitation would likely start higher up. One set of such locations are near the Earth-Moon L4 and L5 Lagrange Points. These are stable regions, but not singular points. The Sun's gravity and the Moon's orbit not being circular or in the same plane as the Earth and Sun cause some motion around the points.

 Delivery, refueling, and maintenance of high orbit satellites from Earth are current and near-term activities for this region. Future activity can include supplying fuel and other supplies from space sources back to low orbit and to early interplanetary locations. These and other possible future activities depend on bringing costs down to affordable levels. This would happen incrementally as self-improving production for early markets bootstraps to larger levels.

 There are some civilization-level problems that high orbit activity can help with. If climate change solutions on Earth are not enough, orbiting sun filters can be used. They let wavelengths used by plants through, but block other parts of the solar spectrum. This would help cool the planet. Large solar system objects that pose a risk to Earth could be diverted or put to use instead. This requires finding them far enough in advance to change their orbit. An active civilization and biosphere off-planet could restore Earth if catastrophes happen despite our best efforts.

 The solar energy flowing through this region is nearly 500 million times what civilization uses today. The Moon and nearby asteroids can supply 250 million years of raw materials at Earth's current mining rate without recycling. With abundant energy and recycling a small fraction of these resources can make civilization sustainable for a very long time.

Transport from Other Orbits

 Excluding the Moon, the high orbit region is nearly devoid of raw materials. So they must be imported from elsewhere. Current transport from Earth uses a rocket to reach orbit, then more chemical or electric propulsion to reach higher orbits. Electric propulsion is about ten times more fuel-efficient than chemical rockets, and is being used more in recent years.

 Electric engines need large amounts of power to operate, but efficient and lightweight solar panels have been developed in the last few decades (see NREL Efficiency Chart). The engines are low thrust, which would expose people and some other items to too much radiation while crossing the Van Allen belts. So some early transport will use less efficient but faster rockets. Once propellants and bulk mass for shielding are available from space sources, the penalty for less efficient transport can be reduced.

 Bulk materials mined from NEOs (Section 2.1) are not time- or radiation-sensitive. They can be transported entirely by electric engines on tugs that make multiple trips. Since part of the product from these objects is more fuel for the tugs, the transport becomes self-sustaining once started. A tug can return about 750 times its hardware mass over a 15 year working life, while consuming about 17 times its mass in propellant over the same period. Tugs can also efficiently deliver hardware and finished products to other orbits as needed.

 The Moon is small enough that bulk materials can be thrown directly into orbit by electric catapults. Assuming 50% efficiency and 50% duty cycle from lunar night, a solar panel can power throwing 1000 times its own mass per year for a 15 year operating life. If the catapult is not too heavy relative to the total mass it can throw, the overall mass return ratio is high. From low Lunar orbit, electric tugs take over and deliver the materials for processing. There are about five major "ore types" of different compositions on the Moon and NEOs: highlands, maria, carbonaceous, stony, and metallic. Using all of them would supply the widest range of raw materials to make the widest range of products.

High Orbit Production

 Energy is needed to convert raw materials into finished products. High orbits have abundant Solar Energy, up to 11,930 kWh/m²/year. It can be converted to electricity by solar panels or used directly for heating using concentrating reflectors. Modern space solar panels and reflectors are very light weight relative to their power output, since they don't have to withstand gravity or weather. Excess heat can be disposed of by radiators or natural Emittance. Low temperatures can be reached with Thermal Shades to block the Sun and other heat sources, and active refrigeration if needed.

 A set of solar panels can supply enough power to start production, since electric power has many uses. Early processing, fabrication, and assembly equipment would come from Earth or low orbit. The first set of products are simple items to be used directly, such as shielding mass, fuel, and basic construction materials. The early production equipment would be supplemented over time by items made in orbit. Over time high orbit industry would transition from importing everything, to making items locally, then exporting products to other destinations.

 Given sources of raw materials and energy, the simplest product of all is radiation shielding for people and equipment. This only requires crushing and sorting, then packing into containers around areas that need protection. Shielding also acts as thermal insulation and impact protection. Shielded modules allow extended crew stays in high orbit. Crews can operate production equipment and perform economic tasks for others, like satellite maintenance and refueling. To some extent the crew can be helped by remote control from Earth.

 Next in difficulty, but not necessarily in priority, are water and carbon compounds, extracted from Carbonaceous-Type Asteroid material. This requires 200-300 C temperatures, which reflectors can supply, and a container and condenser to capture the vapors. Water and carbon can be chemically reformed to oxygen and hydrocarbons, which are common high-thrust rocket propellants. This is useful when transporting people through the radiation belts or for landing on the Moon. They can also be used in electric engines for higher efficiency at lower thrust. Water, carbon compounds, air mined from low orbit, and possibly rock for soil can supply greenhouse modules, so that crews can produce their own food and recycle life support supplies.

 Metallic or M-Type Asteroids are thought to be the source Iron Meteorites found on Earth and Mars. They make up about 5% of known asteroids, with the metal portion being an iron-nickel alloy. A high temperature furnace can melt the alloy, a small amount of carbon added to make a steel alloy, and then cast into basic shapes.

 Steel makes up about 90% of all metal used on Earth. Being able to produce it from space sources would allow a much higher percentage of self-production in space. Subtractive and additive Machine Tools are used to turn basic metal shapes into finished parts. Those can be assembled, along with some imported items, into new machines, including more machine tools. New machines and constructed metal items can then work with other materials.

 Other space-made products can include Basalt Fiber made from lunar basalts, and Carbon Fibers from asteroid carbon compounds. These are are very high strength-to-weight. Fiber-reinforced metal structures are strong and relatively light weight. They would be useful for all kinds of construction.

 Vacuum Deposition is relatively easy to do in high orbit since vacuum is the natural state of that region. Products can include lightweight reflector sheets, and parts for radiator panels. These can be combined with high-concentration solar cells from Earth to supply power with less mass than complete panels. Refractories are a class of materials that can withstand high temperatures. Some were formed in high-temperature environments in space, and others can be made artificially. They are used in all kinds of industrial processes such as furnaces and cooling systems for thermal processing of materials.

 In the long term, in-space production can supply up to 98-99% of the mass for space projects, greatly reducing what needs to come from Earth. The remaining 1-2% includes materials too rare in space to usefully mine, and products too hard to make relative to importing from Earth. Examples are electronics and drugs, which are already mass produced and high value for their weight. Importing them is easier than trying to make them.

Living in High Orbit

 After science and and supporting existing satellites, the first people to spend much time in high orbits would be there to build up industry. But ultimately large, comfortable space habitats can be built as permanent living space, like towns and cities on Earth. Like the ones on Earth, they don't have to be built all at once. The first ones can be small, and attached to industrial production facilities.

 Larger residential habitats can also start small, but be designed to grow over time. Growth can be linear or in layers, like an onion. Linear growth can start with modules attached in a ring, with solar panels attached to each. The ring can be spun for artificial gravity. Additional rings can be stacked with the first one, with a ring of reflectors to direct sunlight to all the panels.

 Layered growth adds new pressure shells over compartments outside the previous ones. The outer shells are in vacuum, and provide radiation, meteor impact, and thermal shielding. Inwards of that are pressurized areas for storage and mechanical equipment. Then comes living quarters and a central open space. The entire habitat rotates for artificial gravity. As new layers are added, items are moved outwards to fill the larger space. Compared to building a large habitat all at once, this spreads the construction cost over time, and the habitat is only expanded when extra space is needed.

8.4 - Phase 4C: Inner Interplanetary Locations

 

Inner Interplanetary Features

 These are orbits detached from the Earth's dominant gravity and go around the Sun instead, though they may pass close to the Earth at times. They range from as close as equipment can function to the Sun to 1.8 AU. This is just beyond Mars' greatest distance from the Sun (1.666 AU) and where the Main Asteroid Belt starts. It excludes Mercury, Venus, Earth, and Mars, and orbits around them.

 Solar power is available 100% of the time in these orbits, but the intensity varies from 31% to many times that near Earth, depending on Solar distance. Exposed temperature correspondingly varies from 244K (-29C) to very hot for dark objects, and less for bright or reflective ones. Travel time from Earth can range from months to years depending on orbit and propulsion method, and whether gravity assists from the planets are used. These save fuel, but usually require extra time.

 Solar and cosmic radiation are a moderately high background, with occasional flares/solar particle events that are much more intense, up to lethal human levels without shielding. Ping time ranges from a few seconds for orbits crossing near Earth, to over 45 minutes at 1.8 AU on the far side of the Sun, by way of a relay satellite. The Sun interrupts direct communication to the opposite side.

 As noted in section 2.1, there are nearly 32,000 known NEOs as of April 2023, and the number is currently increasing by 10% a year. There are another 1500 which don't come closer than 1.3 AU to the Sun and orbit within 1.8 AU on average. The largest among both sets, 1036 Ganymed isn't particularly easy to reach, but has about 100 times the mass of all the rock ever mined on Earth. So total material resources in this region is large.

 Asteroid orbits vary in size, are typically not circular, and somewhat tilted with respect to Earth's, so the energy required to reach a particular one varies. Timing also matters, since everything moves at different speeds in solar orbits. Efficient travel depends on a vehicle and the target arriving at the same place at the same time. The composition of asteroids vary across about a dozen spectral classes, indicating different chemical compositions.

 There are not many active comets in this region because the Sun's heat evaporates their ices in a short time. About 25 Minor Planets and Comets have been visited by spacecraft so far. Most of our knowledge is from telescopes and examining meteorites that have fallen to Earth, and sometimes radar if they come close to us.

Economic Uses

 There are only a few spacecraft currently in this region. They are mostly scientific probes in transit to other places, or stationed at the Earth-Sun Lagrange points 1 and 2 (ESL-1 and ESL-2). Future use is likely to start with asteroid mining and delivery to Earth orbit with electric tugs. About 75% of discovered asteroids in this region are more than 30 meters in size. This is due to limits of current telescopes rather than actual numbers, and may change with time. 30 meters implies a mass of 20-100 thousand tons depending on composition. This is too heavy to move whole with near-term propulsion. A method that should work with all sizes is scraping loose material or grabbing boulders from asteroid surfaces.

 Prior to mining, prospecting missions should visit multiple candidates for geologic mapping and sampling. Mining would start with asteroids that are easy to reach from Earth orbit, and return bulk ore there to be processed. As Earth orbits become more developed, they can start to send production and habitat equipment to this region in addition to mining. Since raw materials and full-time solar energy are available, this can grow in time to full size factories and produce habitats, vehicles, and whatever else is needed locally.

Inner Interplanetary Transport

 The early transport in this region would be mainly slow but efficient electric tugs. They can haul large loads of rock relative to their mass, up to 1000 tons for a 10 ton vehicle and 23 tons of propellant. This will vary with the orbit destination and velocity changes needed. Smaller cargo loads can be moved faster with the same propulsion.

 Gravity Assists can be used if the Moon and inner planets are in the right positions. Chemical rockets would be used when fast velocity changes are needed. Solar sails may be effective in moving things even more slowly but with no propellant use. This depends on large lightweight reflectors delivered to or made in orbit.

 Over time, a network of "transit habitats" can be built up. These are stationed in repeating orbits between planets and particular destinations. They would be larger, safer, and more comfortable than individual passenger vehicles. They can self-supply from nearby asteroids. This reduces having to send life support equipment and supplies each time for the relatively long trips in the region.

 Rotating platforms called Skyhooks can be built to provide both comfortable gravity and fast velocity changes. The platform mass stores momentum from very efficient propulsion that can be exchanged with payloads arriving and departing. The platform needs to be relatively heavy relative to each payload, so it doesn't change its own orbit much in use. Natural asteroids, production "slag" (leftover material not used in products), and the platform's own structure and equipment can serve this purpose. If traffic is balanced in direction, the net orbit change will be minimal.

 Skyhooks can serve as a space equivalent to airports - mainly used to get from one place to another. Like airports, they need enough traffic to justify their construction, and can be developed and upgraded over time. Building them is easier if high strength materials can be produced locally in space.

Inner Interplanetary Production

 Global primary energy consumption on Earth was 18 TeraWatts in 2021. This includes mining, processing, and manufacturing about 2 million kg/s of materials. So the energy intensity of civilization is 9 MJ/kg on average. We will double this to allow for recycling of materials in space, and add 8 km/s of orbit velocity change, requiring 300 MJ/kg of electric tug power. That covers a reasonable range of interplanetary orbits.

 Transportation rather than production is then the dominant energy use in this region for new materials that need delivery. Modern space solar arrays typically product about 100 W/kg near Earth, and would take 36.8 days to produces the required 318 MJ. With a useful life of 20 years, their total energy output is 200 times that needed to transport their own mass in raw materials and all other energy needed to make replacement panels. Concentrating reflector and nuclear power sources are not yet developed enough for space to do calculate energy return ratios. They may turn out better or worse than solar panels, but as long as we have one known energy source with a high return ratio, we can base space industry on it.

 The same process of bootstrapping production in Earth orbits can be used in interplanetary space. This starts with mining for export, then simple products made locally, and gradually growing to make more complex ones. As distance from Earth increases, fewer raw materials would tend to from the Moon, and more from nearby asteroids. These asteroids are of different types, which provides a reasonable variety of materials to work with.

 If we restrict ourselves to within 20 degrees of the Ecliptic, to maintain access to the planets and keep velocity changes lower, we have access to 1/3 of the Sun's total energy, or 1.3 x 10^26 Watts. This is 7 trillion times our current energy use, a number so large it is hard to imagine it could not sustain civilization.

Living Beyond Earth Orbit

 Once methods of living in orbits around Earth are developed in the previous phases, doing so in solar orbits beyond the Earth-Moon region can use the same basic technologies. The main adjustments would be for available solar energy and temperature with distance from the Sun, and the kinds of materials found relatively nearby in velocity terms. In space, velocity changes take work, while coasting to a destination merely takes time.

 It isn't yet clear if a "hunter-gatherer" or "sedentary" lifestyle would be more effective. The first means moving equipment to new asteroid locations as needed, while in the second the it stays in a particular orbit, and materials are brought to it. Since everything is in relative motion around the Sun, opportunities will change with time. So choosing a particularly useful asteroid as a home location may be a good strategy.

8.5 - Phase 4D: Mid-Interplanetary Locations

 

 Living and working in the next region out from the Sun is a smooth continuation of the previous phase, but is different in having lower levels of solar energy and much larger amounts of raw materials.

Mid-Interplanetary Features

Figure 8.5-1 - Main Asteroid Belt and Jupiter Trojan region.

 This region includes orbits from 1.8 to 6.0 AU in semi-major axes (Figure 8.5-1). As of 2023 this includes dwarf planet Ceres, 1.18 million other Main Belt asteroids, over 5600 Hildas, which are in 3:2 resonance with Jupiter, and over 12,500 Jupiter Trojans that occupy the Lagrange regions ahead of and behind the planet. It does not include Jupiter itself and the region within 20 million km of the planet (Section 9.4).

 There are around 450 known comets in the region. The Frost Line for water is in this region at 2.7-3.2 AU. So this is where many comets become active (give off gas and dust), making them easier to find. Hydrogen and oxygen are the 1st and 3rd most common elements, and helium (2nd) doesn't make compounds. So water is the most common compound of two elements. Objects beyond the frost line tend to have have large amounts of it.

 Solar power is available 100% of the time except shadowed areas on and around objects. Intensity varies from 31 to 2.78% of that near Earth. Temperature varies from 244 to 217K (-29 to -56C) for black objects, and less for lighter colored ones. Travel time from Earth is months to years on minimum energy transits, with high to lethal radiation levels for unprotected people. Ping time varies from 13 to 120 minutes, including a relay to avoid a direct path through the Sun.

 The vast and growing number of known objects in the region have a total mass of about 3 billion Gigatons, which far exceeds the Earth's total mining output of about 60 Gigatons/year. About half the total mass is in the four Largest Asteroids: 1 Ceres, 4 Vesta, 2 Pallas, and 10 Hygeia. Composition varies considerably between asteroids due to differences in their formation and history. Velocity to reach orbit from the largest body, Ceres, is only 270 meters/second, or 860 times less kinetic energy than from Earth. So all these objects are easy to access once you are near them. The main energy cost is in adjusting your orbit around the Sun.

Economic Uses

 This region has very few of spacecraft at present, so most uses are in the future. Abundant raw materials of diverse composition, and adequate amounts of solar energy when concentrated, will enable mining and transport to earlier locations as early activities. Previous locations have higher solar intensity for production and habitation. When it makes sense to do so, seed factories and other advanced technologies can help bootstrap a full range of local industry, and eventually large scale habitation. There is enough material and energy in this region to support a full civilization.

Mid-Interplanetary Transport

 The same transport methods can be used in this region as for the inner interplanetary region. The main difference is adding reflectors to solar panels to make up for the lower solar intensity. Electric catapults and skyhooks are somewhat more efficient for injecting bulk cargo to transfer orbits, because they do point acceleration rather than spiral orbits. If a large asteroid absorbs the reaction force, they also don't need propellant. Gravity assists from the inner planets and Jupiter can also increase efficiency.

Mid-Interplanetary Production

 The inner parts of this region have enough sunlight for solar panels to produce power directly. In the outer regions, solar panels benefit from reflectors to increase the light intensity. Concentrating reflectors can produce higher temperatures at all distances, either for industrial processes or habitats. Increasing amounts of reflectors are needed as you get farther from the Sun, but they are inherently lightweight in a zero gravity environment with no weather. Note that the total amount of solar energy available in this region is the same as for the Inner Interplanetary region. It has simply traveled farther and is more spread out. The difference is access to larger amounts of raw materials.

 Asteroids are covered in a mixture of rocks and dust of varying sizes. This is the result of repeated impacts over their life and gravitational attraction. In fact, some asteroids are so low in density that they must be "gravel piles", with no solid central body. Since most asteroids are small, the rocks and dust are easily disturbed and can become a hazard to mining and production operations. So material has to be removed carefully without too much disturbance. Alternately the mining area or the whole asteroid can be covered to contain loose material.

 More distant asteroids and comets contain water and other volatile compounds. These can be extracted separately by heating. Bulk or separated products are then moved by tugs to factories for later production steps. For larger operations, a shell can surround the whole asteroid, keeping gas and dust contained. Processing equipment can then be attached to the outside of the shell, and materials delivered continuously until the asteroid is consumed. The mining and production unit can then move to another target, or the target moved to the unit, whichever is lighter.

8.6 - Phase 4E: Outer Interplanetary Locations

 

 This region is again a continuation of the previous one, with even less solar energy and about 40 times more available materials.

Outer Interplanetary Features

 Outer interplanetary orbits range from 6 to 60 AU in semi-major axis. The areas close to Saturn, Uranus, and Neptune are excluded. They are accounted for in Phase 5E (Section 9.5}. As of 2023 there are over 500 known Centaur objects. These have orbits among the four giant planets, whose gravity makes them unstable over a few million years. There are also thousands of known Trans-Neptune Objects with orbits beyond that planet, making a total of about 3800 in this region. Some, like Pluto and Eris, are large enough to be considered Dwarf Planets. The remainder are in the range of 15 to 850 km, with the lower end set by our current telescopes' ability to find them. There are undoubtedly smaller ones that are undiscovered.

 Available solar power is low, from 2.78% to 0.0278% of near-Earth values. This requires large reflectors to increase intensity, nuclear fission or fusion (if developed), or beamed energy from closer to the Sun. Ambient temperatures are extremely cold, from 160 to 50K for black objects, and lower for lighter ones. Travel time from Earth is typically many years, with high to occasionally lethal radiation levels for unprotected people. Ping time is 1.4 to 17 hours.

 The number of known objects is much smaller than the Mid-Interplanetary region, but their mass is roughly 40 times larger - about 2% of Earth or nearly double the Moon. With increasing distance from the Sun, gases and ices with lower boiling points condensed from the original Solar Nebula. So there is more water, ammonia, nitrogen and other frozen materials, along with rocks and metals. The distinction between asteroid and frozen comet becomes fuzzy, so we call all of them 'objects' and the smaller ones 'minor planets'.

Outer Interplanetary Activities

 This region is likely too far to use with current technology. Activities beyond science and exploration are far enough in the future that technology is likely to change in unexpected directions. When other activities would start and what they will be is undertain, but we can speculate based on what we know today. The raw materials in the region are different than those closer to the Sun. So the first activities are likely to be mining materials scarce closer to the Sun, and bringing them to where there is more energy to process them.

 Due to weak sunlight in this region, nuclear propulsion and gravity assists from the larger bodies are likely to be major transport methods. The solar system has a limited amount of natural Radionuclides that can produce useful power levels. If Fusion Power is not developed enough, they can be made artificially near the Sun where abundant energy is available. If nuclear fusion is well developed, there is abundant hydrogen from which fusion fuels can be produced.

 As distance increases from the Sun, orbit velocities and required velocity changes decrease as the square root of. Solar flux decreases faster, as the inverse square of distance. So solar sails become less effective than for closer regions. Beamed energy from close to the Sun is a possibility. It requires large optics to focus the beam to a reasonable size at destinations in the region.

 We don't expect a lot of production here at first. Water and nitrogen are very useful and found in large amounts. Transport would be slow using minimum energy trajectories. If there is enough demand, a "pipeline" of bulk cargoes in transit could be set up, with vehicles at each end to set them on course and collect them at the end. The cargo can coast in between, saving on vehicle use. Once the pipeline is filled, then cargoes arrive on a regular schedule.

 If lightweight solar reflectors or fusion are developed enough, a full economy based on them may develop, with full production and habitation. We don't see a strong reason to live this far out rather than the warmer and brighter inner regions, but such reasons may develop.

8.7 - Phase 4F: Distant Orbit Locations

 

 The previous three phases are called 'interplanetary' because they are among or near the eight known major planets. This last region is beyond all of them so we call it 'distant'.

Distant Orbit Features

 Distant orbits range from 60 AU in semi-major axis to the limits of the Sun's dominance at about 100,000 AU. As of 2023 there are about 1200 known asteroids and comets in the region. It includes about 650 Scattered Disk and Trans-Neptune objects, and a similar number of Long Period and Near Parabolic comets.

 A few of these objects belong to much larger and more distant populations known as the Hills and Oort Clouds. For our purposes we define these as orbits with axes from 2000-10,000 AU and 10,000 to where passing stars, gas clouds, and galactic tides make orbits unstable. This is roughly 100,000 AU. The existence of comets whose orbits extend to these distances argues for the cloud's existence. Otherwise no active comets would be left after billions of years. Their total number and mass is only guessed at, but may be billions to trillions and multiples of the Earth's mass. There is some evidence to suspect a major planet is also in this region.

 Current telescopes are limited to finding objects within about 80 AU from the Sun. So only the ones that come within the 60-80 AU range at their closest and are currently at the near end of their orbits have been found to date. We expect to find many more objects in the region as telescopes improve. Active comets from distant orbits which come close to the Sun give us some information on composition from the gas and dust they emit.

 Solar energy is very weak in this region, below 0.0278% of that near Earth, and temperatures are extremely cold, from 50K down to near the cosmic background of 2.7K. Travel time with current propulsion technology is many years to centuries. Ping time ranges from 14 hours to 3 years.

Distant Orbit Activities

 Our current information about objects in this region is poor. So any uses beyond science and exploration are deferred to the far future. When that time comes, though, there is a very large reserve of materials that can be put to use. One identified use is the Sun acting as a gravitational lens, with a focus around 800 AU from the Sun, in the Scattered Disk region. Placing telescopes directly opposite a star of interest would allow much more detailed observations than otherwise possible, because of the 2 million km optical diameter of the Sun as a lens.

 To keep transport times within reason, very high energy propulsion would be needed, such as nuclear fusion. Since the light elements needed for fusion are common in these outer regions, this could be self-fueling once set up. Unfortunately, fusion is not yet a viable technology. Transport that uses it remains speculative at present. Due to the low to nearly non-existent solar energy in this region, nuclear energy sources would likely be needed to even consider local production. Production must remain speculative at present.

9.0 - Planetary System Locations

 

 The planetary systems of Phase 5 are different in several ways from the orbital locations in Phase 4 and from each other. Specific designs are needed to handle the differences, so we identify separate sub-phases for each. First are their gravity fields, which require energy to travel through and create significant surface gravity. Second are their large sizes relative objects in the orbital regions, and third is the diversity of conditions found on and around the planets.

 Reasons to use planetary systems include access to the different raw materials available, relief of Earth's biosphere by moving industry off-planet, and some people's preference for natural environments. As with orbital locations, the start of each sub-phase is staggered from nearest to furthest, and is preceded by orbital transport that can reach them carrying useful amounts of equipment. So Phase 4 and 5 projects will overlap in time.

9.1 - Phase 5A: Lunar Locations

 

 Earth is one of the eight major planets in the Solar System. It is already occupied and developed, and we covered using our technical approach earlier in this report. We also covered most orbits around Earth in Sections 8.2 and 8.3. The exception was the Moon and the area around it. We place it here among other planetary systems since lunar activities are more similar to those for smaller planets and the larger moons of the other planets.

Lunar Features

 The Lunar region includes the Moon itself, and orbits with semi-major axes below 35,000 km . These are close enough to be relatively stable. Lunar orbits in general are somewhat unstable. The Moon has mass concentrations from past impacts that create an uneven gravity field (Figure 9.1-1). The Earth and Sun are also much more massive than the Moon, and have significant effects on objects orbiting it (Gordienko, 2018).

 The Moon has the same average distance from the Sun as the Earth, so available solar energy and basic temperatures ranges are the same. Sunlight is partly blocked in lower Lunar orbits, and blocked about 50% of the time on the surface over a 29.5 day cycle. Surface gravity averages 1.62 m/s², or 1/6th of Earth, with a total variation of 0.025 m/s² by location.

 Escape velocity from the Lunar surface is 2380 m/s, or 21% of Earth. So escape energy is only 4.5% of Earth's. Low orbit velocities are 1680 m/s or less, and 700 m/s more is needed to escape from them. Circular orbit velocity at the upper edge of the region is 375 m/s, and escape is an added 155 m/s. Surface area of the Moon is 37.93 million km^2 measured horizontally, or about one quarter of the Earth's land area. Sloped terrain increase the total exposed surface area.

Figure 9.1-1 - Lunar surface gravity map. Near side on left, far side on right.

 Earth is only 81.3 times the Moon's mass. So the center of mass of both averages 1/4 of the way down from the Earth's surface to it's center. Both move around this center every 27.3 days with respect to the stars. Since both also orbit the Sun, the Moon's orbit and day lengths are not the same.

 The Moon is tidally locked to Earth, and keeps approximately the same side facing us. It is not exact because the Moon's orbit is not circular, it has a slight residual pendulum motion, and we have different vantage points from the Earth's surface. So about 59% of its surface can be seen from Earth over time. The two hemispheres are called the "near" and "far" sides. There is no "dark" side, since both get sunlight during a lunar day.

 Orbits around the Moon vary from 108 minutes close to the surface, to 6.8 days for the largest ones in the region. Travel time from Earth is 3-4 days for direct transfer orbits. Electric propulsion is much more efficient, but also much slower. Without shielding, travel to and staying on and around the Moon can expose people to lethal radiation levels. This is from Earth's radiation belts, solar, and cosmic sources. Ping time from Earth to the Lunar region varies from 2.2 to 2.94 seconds, depending on where in the region, and the Moon's distance in it's orbit. This includes satellite relay time if communicating with areas that can't be seen directly from Earth.

 The Moon has a somewhat variable and reasonably well understood Geology. This is known from a number of lander and orbital missions, some of which returned samples, and Lunar Meteorites thrown to Earth by impacts. Broadly, the surface is oxide minerals with silicon, iron, calcium, aluminum, and magnesium, in order of abundance, and 3-4% other elements.

 The Moon is too small and warm to keep an atmosphere. With nothing to stop them, the surface has been heavily cratered and broken up by repeated impacts of all sizes. The result is a Regolith or lunar soil that has been tossed around many times. It is a mix of the original crust and the remains of impacting objects. There is no weathering like on Earth, but the solar wind can charge dust particles which then move, and temperature cycles cause rocks to crack near the surface.

Economic Uses

 The Lunar region is embedded in the High Orbit region, and reaching it from Earth is possible with current and near-term transport. Science and exploration activities are already in progress. Further development can start as soon as there are economic reasons for it. The first uses are likely to be local on the surface, and from the Moon's relative closeness to populated satellite orbits and low energy to reach these orbits. For example, some Water appears to be trapped in cold polar craters on the Moon. It has multiple uses, and could be delivered relatively efficiently to high and low Earth orbits.

 Regolith mining can supply enough materials for much larger projects on the Moon and nearby orbits. The loose surface layer averages 5 meters thick across the whole Moon. It can be collected without using heavy equipment and totals about 300,000 Gigatons, or 7,000 years of Earth's total stone and sand mining in 2020. Projects that use lunar (and asteroid) materials are not as limited by launch mass and cost from Earth, so they can use simpler and heavier designs. In the future, production that uses lots of energy, or have hazards and side effects, could be moved to space to reduce the burden on Earth's environment.

 Satellites that beam energy to Earth is one possibility. If this can be done economically, it might become the largest export market from orbit. Renewable energy on Earth is now relatively low cost, but it is variable and some places have poor conditions for using it. There is 10 times more solar energy in space than such places and it is more predictable. So it may prove useful, despite the extra cost of building in space.

Lunar Transport

 Early landings on the Moon would not have the support of much infrastructure. They would use current high thrust chemical rockets to access the surface. At first, all propellants would come from Earth. Water from polar lunar craters can supply 83.5% of methane/oxygen propellant, and and also life support supplies, reducing the mass needed from Earth. Carbonaceous type asteroids contain up to 20% carbon compounds and water. These can be reformed chemically to CH₄ and O₂ and fully replace Earth supplies. How much would come from each source will depend on cost and availability.

 Over time, chemical propulsion can be replaced by more efficient methods. As mentioned in Section 8.3, an electric catapult can deliver 1000 times a solar array's mass per year from the surface to Lunar orbit. Electric propulsion can then move lunar and asteroid materials a common orbit for processing. High orbits around the Moon or Earth are preferred for their near-full time sunlight and a combined low velocity to reach. Both propellants and other products can be made with processing and manufacturing equipment in the same location.

 Lunar basalt and carbon from asteroids can be used to make high strength fibers. These can be used to build an efficient skyhook system in lunar orbit. Such a system makes sense if there is enough traffic to the Moon. If the tip velocity is equal to orbit velocity they cancel, and trips to the lunar surface would need very little fuel. A lander can be dropped off and picked up at low altitude. It would not be dropped directly on the surface because of the variable gravity field and heights of lunar mountains and crater walls.

 If the skyhook is in near-polar orbit, it can access any point on the surface every 15 days as the Moon rotates below it. Using other angles of the skyhook's rotation, and by climbing to different distances from the center, arrival and departure directions and speeds up to 1.41 times lunar escape are possible. Catching and releasing vehicles affects the skyhook's orbit. If traffic is balanced in direction and mass, and the skyhook is massive enough, it is a temporary change. If traffic is more in one direction than the other, the difference can be made up by electric propulsion at high efficiency.

 Low gravity is known to be harmful to people. If the skyhook radius is about 250 km, the tip acceleration will be about 1 g, which avoids this problem. A large supply of lunar materials can supply shielding. With these people can live comfortably and safely. They are close enough to the lunar surface to operate equipment by remote control in real time. Alternate solutions are using rotating habitats on the surface or limiting stay times.

Lunar Production

 The advantages of using the Moon are relative closeness to high orbits, and low energy to move cargo. But there are few low boiling-point materials left on the Moon, because it formed in a molten state, suffered many high energy impacts and early tidal heating, and is too small to keep an atmosphere. A fully-developed space economy would need to supplement lunar materials with those from nearby asteroids and from Earth. Some materials are too rare to usefully mine in space, and some products are too hard or expensive to make there relative to delivery from Earth. So two-way trade can develop for lunar activities to support themselves.

 Early Lunar production can start with mining bulk regolith for radiation/thermal/impact protection, and polar ice for propellant and life support. These don't need a lot of complex equipment. More energy-intensive and complex processes like vacuum oxide reduction and Carbothermic Reactions can separate oxygen and various metals from the regolith. Seed factory equipment can be used to bootstrap making other products for local use and export. As better transport systems are installed in sequence, the cost of delivery elsewhere will decrease.

 Solar energy will likely be the dominant energy source for lunar production. Silicon for solar cells, aluminum for reflectors, and other metals for structures are widely available from the regolith to provide solar power. However some craters with water are permanently shadowed, the lunar night is two weeks long, and large solar plants are not very portable. So other energy sources may be useful.

 Some regions of the Lunar surface contain ~10 parts per million Uranium and Thorium. The ore has an energy content of about 800 MJ/kg (20 times that of coal on Earth). Helium-3 has been proposed as a fusion fuel to be mined from the Moon. Although the energy content of pure He-3 is 200 TJ/kg, the concentration is only 15 parts per billion or less, resulting in an ore content of only 3 MJ/kg. So fissionable elements are a better energy source on the Moon in terms of energy produced per ton of mined ore.

 Other energy sources for the Moon can include the rims of shadowed craters, where sunlight is highly available, microwave or laser beamed power across terrain or from orbit, and even fuel cells or batteries for portable power. Thermal energy storage is an option using the vast amount of rocks and dust as the storage medium, and the natural vacuum as insulation. The material is heated during the day by sunlight, and the heat used to generate power during the Lunar night.

Living in Lunar Locations

 Low gravity is known to be harmful, so long-term habitats on the Lunar surface may require rotation to create artificial gravity. An example would be a large habitat dome for spaciousness, and a centrifuge built around the rim for living quarters. Residents would spend enough time in the centrifuge to maintain health, but could work and enjoy the low gravity the rest of the time.

 We have essentially no data on how much gravity is enough between zero and 1.0. We know the body deteriorates over time in zero gravity. So as a worst case, people would need to spend most of their time in a one gee environment of some type, but this subject needs more research. Another option is limiting permanent stay times on the surface. People would live mostly in orbit with artificial gravity and operate most equipment by remote control.

 The other requirements for people to live and work in the lunar region have mostly been solved by existing space stations, and using bulk materials for shielding. One exception is lunar dust, which is abrasive, toxic, and is everywhere on the surface. Various methods to deal with it have been proposed, but R&D is needed to figure out which work best.

9.2 - Phase 5B: Mars Locations

 

 Mars is next among planetary locations in terms of velocity and time to reach, and the environment conditions there. It is a large step beyond the Moon, but Mars is within the inner interplanetary region (Section 8.4) that Earth also occupies. So we expect Martian activities to start after some level of development of the region in-between.

Mars Features

 The Mars region includes the planet, two small moons, and reasonably stable orbits with semi-major axes up to 340,000 km (100 radii). Its orbit around the Sun is 9.3% eccentric, varying from 1.38 to 1.67 AU in distance. Solar flux varies with distance from 494 to 716 W/m², or 36 to 52.5% of that near Earth. Surface gravity varies from 3.683 to 3.743 m/s², a 1.6% range, with a reference value of 3.711 (3/8ths of Earth). Lower values are near the equator and atop tall mountains, while higher values are at lower altitudes in the north polar region and Hellas basin.

 Ping time from Earth varies from 6 to 45 minutes, depending on relative orbital position and need for a relay satellite to avoid the Sun. Unprotected radiation levels range from high to lethal, but the Mars surface and its moons provide ample material for shielding.

 Escape velocity from the surface is 5,027 m/s, and is 502 m/s at the upper edge of the orbital region. Circular orbit velocities are 70.7% of escape. This ratio holds for orbits around any body. Escape energy is 20% that of Earth. Orbits around Mars vary from 100 minutes for low ones to 70 days at the edge of the region. Surface area of Mars is 144.8 million km², or 97% of Earth's land area. Day length is 24h 40m, slightly longer than Earth, and the Martian year is 1.881 Earth years. Travel times vary according to the relative positions of Mars and Earth, and the transport method used. When aligned, minimum energy orbits average 7 months one way.

 The moons Phobos and Deimos have near-circular orbits of with 9,377 and 23,460 km radius. They have mean diameters of 22.5 and 12.4 km, but are irregular shapes. They have a combined mass of 12,800 Gigatons, or 290 years of Earth's rock and sand mining. This is a significant orbital resource. They are likely collected impact debris, so similar to Mars in composition.

Figure 9.2-1 - Generalized geologic map of Mars.

 The atmosphere is 96% CO2, a bit under 2% each Argon and Nitrogen, and an assortment of trace gases. Surface pressure varies from 30 Pascals at the top of Olympus Mons to 1155 Pascals in the Hellas basin. The high value is 1.14% of sea-level pressure on Earth. Pressure varies by 30% annually, as some of the CO2 freezes and evaporates at the poles. Surface temperatures vary from 120 to 293K (-153 to 20 C), depending on latitude and season. Typical day-night variation is 70K/C because the atmosphere does not have much thermal mass.

 Mars has quite a varied surface geology, as a result of internal melting and vulcanism, impacts, and much higher levels of water and atmospheric pressure earlier in it's history (Figure 9.2-1 from USGS Map 3292, 2014). There is significant amounts of water in the soil as hydrates, permafrost, and in thick dusty ice caps.

Economic Uses

 Human activity in the region can begin with a scientific outpost. It would be an extension of existing robotic exploration, and Phase 4C activity among asteroids in the surrounding region (Section 8.4). The outpost and relay satellites are placed in orbit close enough to Mars for real-time remote control. Surface robots carry out science and sample collection at first, with some samples returned to the outpost for further analysis. Most outpost supplies can come from Mars' moons and nearby asteroids.

 Over time, other robots and equipment are delivered to the surface to start to preparing for people. Once enough supplies and basic production are in place, they can start to visit. This approach delays risking people on the surface until a supply chain and reliable two-way transportation is available.

 As more production capacity is built up on Mars and surrounding orbits, it can start to transition from science to prospecting for unique resources, building up local habitation, and a full economy. Since Mars has almost the same land area as Earth, there is plenty of room to do this. Building up activities in the Mars region would be a relatively small extension from previous regions. So it is not a large cost burden, but rather an investment in further growth.

Mars Transport

 In Phases 4B and 4C (sections 8.3 and 8.4 above), electric tugs were used to move asteroid materials back to Earth/Moon orbits for processing. To expand towards Mars, the same type of tugs move materials from Near Earth or Near Mars orbits to specific Mars Cycler orbits. These orbits allow repeat flybys of Earth and Mars using gravity assists. Given the many thousands of asteroids in the interplanetary region, some of them have low velocity to and from a cycler orbit.

 Other tugs deliver habitat modules and initial processing equipment from near Earth to the same orbit. The raw asteroid materials are distributed around the habitat for radiation shielding, and used as a counterweight for artificial gravity. At the next opportunity a crew meets up with the new "Mars Transfer Station", and begins to process the raw materials into fuel, air, water, metals, etc. They also establish a greenhouse to produce food. When raw materials run low, a tug is sent to another nearby asteroid to get more.

 Whenever the Transfer Station is near Earth, new crew, equipment, and supplies can be delivered. Crew aboard the transfer station are safe from radiation hazards, have gravity to maintain health, and can eventually produce most of what they need themselves. The Station can be used multiple times to bring new crews to Mars, saving mass over carrying a life support system and supplies for every trip. Cargo besides people can travel to the Mars region directly with tugs.

 When the transfer station is built up enough, a set of crew detach and inject into Mars orbit. The Martian moons then become a source of materials in addition to nearby asteroids. Eventually enough propellants are produced locally for trips to the planet's surface.

 Chemical rockets consume a lot of propellants traveling back and forth from the surface. In the longer term, some combination of skyhook and surface catapult can replace most of that. These would be large projects, but the propellant savings for each trip makes up for it. Carbon from asteroids or the moons, and basalt from Mars, can be used to make the strong fibers for such systems.

 Skyhooks can start small with low capacity, but their orbit parameters and timing would be shifted from bulk going up. Linear or rotary electric catapults on the surface are attached to the planet and not affected this way. To limit drag losses they would be built on the large Martian volcanoes. Mixed use of both systems is also possible. It is too early to choose among these or other options, but chemical rockets are inefficient. In the long run something better would be preferred.

Mars Production

 Like other phases of our program, the production in the region starts with mining raw materials for basic products with ready-to-use equipment. Seed factory equipment is delivered to orbit and the surface as needed. This bootstraps more diverse, larger scale, and advanced production. The supply chain from Earth and intermediate regions supports this with regular deliveries.

 Mars has a different history than asteroids, so it likely has sources of volatile compounds and minerals not common in the orbital regions. Very efficient bulk transport is desirable for an export market to develop. Because the gravity well of Mars requires large-scale systems to do this, exports may not be economic right away, but rather need a build-up period in the region first.

Living in Mars Locations

 Living in the orbital region around Mars would be similar to high orbits around Earth or the interplanetary region that surrounds both. There would be minor differences in available solar energy and local material sources. Living on the surface would require adapting designs to local conditions of gravity, temperature, and other parameters. Since gravity is 3/8 Earth normal, that includes how to maintain health for people and other living things. Example methods are body weights and rotating habitats.

 Terraforming Mars has often been suggested because it is already the most similar place to Earth. Doing this for a small population is likely too much effort for the amount of use it would get. When the population gets large enough or technology has advanced enough the local population (Martians) can decide if terraforming makes sense. Self-improving production systems can make such a project easier.

 An alternate approach is to use habitat domes to provide a feeling of being outdoors. Internal pressure would be much higher than outside. So lightweight domes need a lot of structure and anchoring to avoid lifting off the ground. Domes can be weighted down by bulk soil and rock, or using thick glass. These also provide radiation, temperature, and impact protection.

9.3 - Phase 5C: Venus and Mercury Locations

 

 Venus and Mercury are the next in difficulty after Mars. They have abundant solar energy available, but as a result are mostly very hot. There are relatively few nearby asteroids to start orbital development with.

Venus and Mercury Features

 The Venus and Mercury regions include the planets, and relatively stable orbits within 600,000 and 100,000 km of their centers, respectively. Like Earth they are embedded in the Inner Interplanetary region (Section 8.4). They have no known moons. So the main interest is the planets themselves and activity around them. Venus' orbit is nearly circular at 0.723 AU, while Mercury's is 20% eccentric and varies from 0.307 to 0.467 AU.

 Solar flux is 1.9 times higher than near Earth at Venus, and 4.6-10.6 times higher at Mercury. Equilibrium temperatures in sunlight are 17% and 46-80% higher in Kelvin. The surface temperature is 735K (462 C) for Venus, from a thick atmosphere with a strong greenhouse effect. Mercury ranges from below 100K in shadowed polar craters, to as high as 700K at the sub-solar point at perihelion. A given location can vary nearly this whole temperature range due to a 58.6 day rotation period. Venus's rotation takes 243 days, but the atmosphere mostly eliminates temperature changes.

 Venus' surface gravity is 8.87 m/s^2 (90% of Earth), and Mercury's is 3.7 m/s^2, the same as for Mars. Escape velocities are 10.36 and 4.25 km/s from their surfaces and 1,041 and 664 m/s from the outer edge of their regions. Orbits range from 90 minutes to 59 days around Venus, and 85 minutes to 15.5 days around Mercury. Ping times from Earth vary from 4.3 to 30 minutes for Venus, and 9 to 25 minutes for Mercury. Travel times by least energy transfer orbits are 4.8 and 3.5 months respectively.

 The Geology of Venus appears to be mostly volcanic, and it has lost most of its water to space. The atmosphere has a surface pressure of 9.2 MPa (90.8 times Earth), and is composed of 96.5% CO2 and 3.5% Nitrogen, with some trace gases. While it is very hot at the surface, moderate pressures of 0.5 times Earth and temperatures around 27 C exist at 55 km altitude. Mercury has only a trace atmosphere, and a Silicate surface about 40% O, 25% Si, 11% Mg, 6% Al, 4% each Ca and Fe, and 2% S. Polar regions can have surprisingly moderate average temperatures, and water ice has been found in shadowed polar craters

Economic Uses

 Near-term use of Venus and Mercury is more difficult because of the higher velocity to reach them and generally hostile temperatures. Scoop-mining gases from the upper reaches of Venus' atmosphere is a possibility. In the mid-term, floating habitats are possible at altitudes where temperature and pressure are reasonable. Polar stations on Mercury can take advantage of lower average temperatures with proper insulation. In the long term asteroid iron or aluminum can be used for orbiting sunshades to cool both planets where needed.

 Reducing temperature lowers the scale height of Venus' atmosphere, and preferentially lowers the pressure of the high altitude regions of the planet, making them more accessible. There is the possibility that low enough temperatures will promote carbonation of the volcanic surface minerals, further lowering pressures, and that this process can be enhanced artificially. If the surface conditions can be made more tolerable, then large scale access to raw materials plus high energy available in orbit could promote industry.

 It takes 7 to 12 km/s velocity change to travel from near Earth to the Venus and Mercury orbit regions, and therefore 0.15 and 0.27 kg of propellant per kg cargo using electric thrusters. This does not account for gravity assists or skyhook transfers. These require 263 and 474 MJ of solar power respectively. If the cargo is all solar arrays, or equivalent thermal power generation, they will produce an additional 13.75 and 91.5 MJ/day added power output, and repay the extra energy use in 19 and 5.2 days respectively. So energy-intensive processes highly favor going closer to the Sun.

Venus and Mercury Transport

 Higher orbit speeds as you get closer to the Sun means more velocity changes are needed to reach them. Like elsewhere, gravity assists and skyhook systems can help do this more efficiently. Solar-powered electric propulsion is quite viable closer to the Sun. Solar flux increases faster then velocity changes, so this introduces the possibility of solar sails as an additional transport method in the inner regions. The advantage of solar sails is they do not consume propellant. But in the outer Solar System low solar energy makes them very slow.

 For example, reflected sunlight provides 15.5 Newtons/km^2 at Venus, and a 1 micron thick Magnesium-Aluminum sail would mass 2400 kg/km^2. This generates 558 m/s/day acceleration for the bare sail. This is reduced by the remaining structure and cargo mass, and by angling the sail to control thrust direction. This acceleration is comparable to that for electric propulsion using solar array mass near Earth. A combined system can take advantage of reduced propellant use from a sail and wider thrust angles from the electric engines.

Venus and Mercury Production

 Production in the Venus and Mercury regions would likely start in orbit as an extension of Inner Interplanetary activity. The higher solar flux relative to energy needed to reach inner orbits favors processes that need lots of energy. Raw materials can come from nearby and imported asteroid sources, and possibly scoop mining gas from Venus orbit. There are only 59 known asteroids whose orbit is entirely inside Earth's, and less than 2500 others whose orbit is smaller than Earth's and cross inside of it. This is only 0.2% of the total known, so many materials may have to be imported from farther away.

 Habitats to support production, with artificial gravity, thermal, and radiation shielding can be built in more developed regions and transported to Venus and Mercury orbit to start with. Surface catapults are possible from Mercury's polar regions, where temperatures are more moderate. The combination of materials delivered at least partly by solar sailing and abundant solar energy should allow production to grow in time.

Living at Venus and Mercury

 Living in orbits around the two planets would be similar to the nearby interplanetary region, and not require much new design. The planets themselves are mostly hostile in their current state, so we expect few other habitats would be built beyond possible science and exploration outposts in the mid-term. If planet-scale terraforming becomes feasible, mostly by blocking excess sunlight, non-industrial habitats may develop in the long-term.

9.4 - Phase 5D: Jupiter System Locations

 

 Development of the Jupiter System would likely follow the Mid-Interplanetary (Section 8.5), as its orbit is near the outer edge of that region. It isn't clear if the Jupiter region will be easier or harder to develop than Venus and Mercury.

Jupiter System Features

 The Jupiter System includes the largest planet in the Solar System (317.8 Earth masses), and reasonably stable orbits around it with semi-major axes less 25 million km. It includes four Galilean Moons more than 3000 km diameter, named as a group after their discoverer. As of 2023 there are 91 known Smaller Moons from 1-170 km in size. The larger moons can support their own reaxonably stable orbits, and can be used for gravity assists to change orbits in the Jupiter system.

 Solar flux varies from 3.3-4.1% of that near Earth, so concentrating reflectors are useful in this region. Escape velocity is 59.5 km/s from just above the atmosphere, or an added 24.6 km/s from low orbit. Escape is 3.11 km/s from the edge of the region. Orbit periods range from 174 minutes to 2.26 years. Travel time from Earth by minimum energy orbit is 2.7 years, while gravity assists and other propulsion methods can increase or decrease the time. Ping time is 1.06 to 1.85 hours, depending on relative orbit locations.

 Jupiter has a strong magnetic field which creates intense radiation belts. This ranges from high to immediately deadly levels for unprotected people, and can rapidly degrade even shielded electronics. Outside these belts, the usual solar and galactic radiation is still a hazard. Temperature in Jupiter System orbits are about 217K (-56 C) for black objects, and less for lighter colored ones. Jupiter is a Gas Giant, and therefore has no solid surface. The atmosphere is 90% Hydrogen, 10% Helium, plus trace gases. Orbit minus rotation velocity is 29.5 km/s, making it very difficult to access the planet itself or even mine the atmopshere from orbit.

 The four large moons (Io, Europa, Ganymede, and Callisto) orbit 0.422, 0.671, 1.07, and 1.88 million km from Jupiter in nearly circular orbits. They have a combined surface area of 232.8 million km^2, or 1.56 times the land area of Earth. They have negligible atmospheres. All four are tidally locked to Jupiter, so their days are equal to their orbit periods of 1.77, 3.55, 7.15, and 16.7 days. Surface gravity varies from 1.23 to 1.80 m/s^2, or 12.5 to 18.4% of Earth.

 Io's surface is volcanic deposits and sulfur compounds. The other three large moons are either entirely or partially covered in ice, with various minerals and frozen compounds making up the rest of their surfaces. Surface temperatures of the large moons range from 70-165K, except for volcanic hot spots on Io, and vary mostly by latitude and how close they are to Jupiter, which determines how much reflected light they get on the near side.

Economic Uses

 Use of the Jupiter System would likely follow the Main Belt and Trojan locations in Phase 4D. There are 12,500 Jupiter Trojans vs 91 smaller moons around Jupiter, and the Trojans are much larger in total mass. Since Jupiter's gravity well requires more velocity to navigate, there is no particular reason to use the smaller moons except as a way to access the larger ones. The outer Jovian moons are likely captured asteroids, and are the same Solar distance as the Trojan group. So they don't represent new technical challenges.

 The large moons together have 6.6% of Earth's mass, or 5.4 times that of Earth's Moon. They can be a very large source of materials, with some significant variations in composition. Early uses are likely to be mining-based, with return of materials to more developed regions. Even the largest moon, Ganymede, has a low enough orbit velocity that a catapult or skyhook can deliver directly to orbit, after which an electric tug can transport it elsewhere. Water is widely available in the Jupiter System, both for life support and propellant. High radiation close to the planet requires careful design for habitats and electronics. Remote control from a safe distance is a possibility.

Jupiter System Transport

 Transport from the Mid-Interplanetary region and closer to Earth can start with electric propulsion, and for people use shielded habitat modules. High-thrust landers can be used to start with for the large moons, while skyhooks and catapults can be brought or built later for higher efficiency. Since these would already be developed for previous locations, not much new design would be needed except for radiation protection close to the planet. Transfer habitats in cyclic orbits with heavily shielded sections is a design option. Those sections are used when when close to the planet. We don't expect to land on or mine Jupiter itself until far in the future because of the extremely high energy required. The other Gas Giants are easier to access and have milder radiation belts.

Jupiter System Production

 Growth of local production follows the usual path of mining first, then bringing seed factory equipment to bootstrap other industries. The smaller outer moons can be an early source of fuel and water. Rocky and metallic materials may need to be imported from the surrounding regions, depending on the composition of the moons. Large reflectors would be a desirable early product to generate power and heat.

Living in the Jupiter System

 Living in the outer parts of the Jupiter system is very similar to the Trojan asteroid regions, as they are the same average distance from the Sun. Only Callisto among the large moons has tolerable radiation levels at its surface. The closer moons and orbits around and among them require significant shielding. Water is a good shielding material, and all the large moons have lots of it.

9.5 - Phase 5E: Outer Giant Locations

 

 The three outer giant planets, Saturn, Uranus, and Neptune, are next in difficulty from distance and lower solar energy. This is compensated somewhat by lower masses than Jupiter, so smaller velocity changes are needed to work around.

Outer Giant Features

 The three planets average 9.55, 19.22, and 30.11 AU from the Sun. These planets and their orbital regions are embedded in the Outer Interplanetary region of Phase 4E (Section 8.6). Saturn's orbital region extends 30 million km from the planet center, and includes 83 Known Moons as of 2023. Eleven of these moons are larger than 100 km, of which five (Tethys, Dione, Rhea, Titan, and Iapetus) are larger than 1,000 km, with Titan being 5,150 km in diameter (75% of Mars).

 Uranus' region is 24 million km in radius, and has 27 known Moons. Five of them (Miranda, Ariel, Umbriel, Titania, and Oberon) are considered major, ranging from 470 to 1575 km in diameter. Neptune's region is 50 million km radius, and has 14 known Moons, of which Triton is by far the largest at 2700 km diameter. The larger moons of all three can support stable orbits and enable gravity assists. All the giant planets, including Jupiter, have ring systems. Saturn's is the most massive at an estimated 30 million Gigatons, almost as much as the 400 km moon Mimas, which orbits nearby.

 Solar energy is weak in these regions, about 1%, 1/4%, and 1/9% of that near Earth. Large reflectors would be needed to bring sunlight to useful levels. Nuclear power may be more effective. Escape velocities are 35.5, 21.3, and 23.5 km/s from each planet, and 1,535, 682, and 255 m/s from the edge of their regions. Orbit periods are vary from 250, 180, and 155 minutes close to the planets, to 3.8, 9.9, and 27 years at the edge. Travel times are 6, 16, and 30 years by minimum energy orbits. Gravity assists and added propulsion can shorten the trips.

 Ping times average 2.65, 5.33, and 8.35 hours, plus or minus about 20 minutes for relative planetary positions. Radiation levels around Saturn are about as high as Earth's Van Allen Belts, so added shielding is needed for people and electronics. It is most intense between the ring system and the moon Enceladus. Radiaition around Uranus and Neptune are lower, but still include the solar and cosmic background flux present in most parts of the Solar System.

 Like Jupiter, the outer Giants have no solid surface. Their atmospheres get denser with depth until they are beyond the Critical Point and reach liquid density and higher. The upper portions are 96% hydrogen, 3% helium for Saturn; 83% hydrogen, 15% helium, and 2.3% hethane for Uranus; and 80% hydrogen, 19% helium, and 1.5% methane for Neptune. All three have small amounts of trace gases. Orbit minus planet rotation velocities are 15.2, 12.5, and 13.9 km/s. Scoop mining their atmospheres would be hard, but should be feasible.

Economic Uses

 The outer Giant regions are too far for near-term use. Their development could start once the Outer Interplanetary region around them is accessible. The first use is likely to be mining various raw materials. The combined total of 124 moons and one major ring system around these planets have a mass of 1720 x 10²⁰ kg, or 2.34 times the Moon. This is a very large source of materials, but their distance means mining them will be delayed. Mined material would likely be brought back back to inner regions where there is more energy for processing and projects that need them. Other uses besides mining are too far in the future to predict right now.

 Titan has a thick Nitrogen atmosphere (1.4 times Earth pressure) with 1.4% Methane at upper levels and 4.9% at lower levels. Low orbits are about 1.8 km/s, so scoop-mining this atmosphere is particularly easy. Helium-3 has been proposed as a low radiation fusion fuel. Fusion in general has not yet been solved, and the He-3 reaction is 10 times harder than deuterium-tritium (D-T), which is the main target of current research.

 If either kind of fusion becomes feasible, scoop-mining the outer Giant atmospheres may become economic because of its high energy output, and the light gases also make good propellants. All three giants have deuterium, and Uranus and Neptune have the highest concentrations of Helium in their atmospheres, and thus the He-3 isotope. The easier D-T fusion should enable trips to these planets in reasonable time.

Outer Giant Transport

 Chemical rockets have sent probes to the outer planets, but this is very inefficient. As in other regions, gravity assists from massive bodies, surface catapults, and skyhooks can be used to improve transport efficiency. Solar power has been used for probes as far as Jupiter and its Trojan asteroids, but reflectors to increase power for propulsion in farther regions hasn't yet been developed. Current work is on small fission reactors for a variety of uses, including nuclear-electric propulsion, which would be much more efficient than chemical.

 Fission and fusion fuels have high energy content but the reactors to use them tend to be higher mass than solar power. The also emit harmful radiation, but most parts of the Solar System are already filled with it anyway. The same shielding can protect from both sources. Nuclear fuels are also relatively rare compared to silicon used for solar cells or aluminum/magnesium alloy for concentrating reflectors. It isn't clear what the best energy source for future propulsion will be.

Outer Giant Production and Living

 We don't expect activities beyond science, exploration, and mining in these regions until technology improves significantly from current levels. Since we can't predict what improvements will be made in the long-term, we will leave what local production and habitation is possible as an open question.

10.0 - Interstellar Locations

 

 The last major phase of our program involves interstellar locations. The key difference that warrants a new phase is the extreme distances involved. This breaks the ability to deliver things from the Solar System and communicate with it in a reasonable time. Deveopment of these locations would require high self-sufficiency in transport, enough starting materials, and self-improving systems capable of growth without outside assistance.

 Phase 6 projects are far enough in the future that we can only speculate about them in general terms. We include it mainly as a place-holder and to give direction for future long-term work. We divide it into two sub-phases - the spaces between stars, and those around other star systems. Since you must cross interstellar space before reaching the other systems, logically the sub-phases are in that order.

10.1 - Phase 6A: Interstellar Space Locations

 

Interstellar Features

 We define the Interstellar region as starting 100,000 AU from the Sun, where nearby stars and the Milky Way galaxy as a whole begin to contest the Sun's gravity. There is no outer limit for this region beyond whatever travel distances are possible from future technology. Since we don't know what those future technologies will be, for now we will arbitrarily set a boundary of 20 light years from the Sun.

 Probably the most significant feature of this region is that star systems are all in relative motion to each other, with an average velocity of 50 km/s. This is on top of the general rotation of the galaxy at about 225 km/s. As of 2023 there are 131 known Stars and Brown Dwarfs in the 20 light year "Solar Neighborhood". Given their average velocity, they will travel 20 light years in 120,000 years, so the membership of the neighborhood will change about every 1250 years on average.

 The local interstellar region is very low density gas, at ~0.3 atoms per cubic centimeter, or 1 gram per 564 km cube. That does not include cometary clouds around stars, or wandering objects between them. We know very little about such smaller objects, but assume some exist by similarity to our own Solar System.

 The Interstellar environment between stars is not much different from distant orbit environments in Phase 4F (Section 8.7). Stellar energy is effectively zero, and while stellar radiation is not a factor in this region, cosmic radiation still is.

Economic Uses

 We don't know enough about material resources and energy sources in this region to propose economic uses. The distance to the Sun detaches any industries from regular trade with the rest of civilization. Science, exploration, and seeding interstellar colonies are possible long-term activities.

Interstellar Transport

 Interstellar transport can be divided into slow and fast types. The slow type is on the order of stellar velocities (5-500 km/s). An example is a large habitat with large material reserves and fusion power as an energy source. It can subsist on the cometary clouds around stars and unbound objects between them. When it gets close enough to a selected star, it can enter orbit and travel with it. Such habitats would be based on previous space habitats in the Solar System, so it doesn't require a lot of new development.

 Travel times between stars at these speeds would average 3000 years or longer. Such times are long enough that technology changes during the trip are a factor. Trying to reach a specific star doesn't make unless technology had reached a plateau or making improvements in transit was planned for. If the habitat is considered a permanent place to live that happens to be moving to access new resources, speed of travel is less of an issue.

&emspFast interstellar puts much more energy into transportation, to reach higher velocities and shorten time to a destination. Possible methods include fusion-powered engines and beamed power using the Sun as a gravitational lens for focus. Rather than a large habitat with a full range of civilized activity, fast interstellar operates more like ships on Earth, with a crew dedicated to reaching a destination and maintaining operations. We don't yet know what interstellar transport methods will prove feasible, if any, and the other space-related technologies available by then, so this is all speculative for now.

Interstellar Production

 We don't know enough about resources in this region to consider gathering raw materials. So the only production we can plan for now is what they bring with them. If they start with a large reserve, such as a captured comet nucleus, it can be used for supplies, maintenance, and upgrades.

10.2 - Phase 6B: Stellar Locations

 

Stellar System Features

 We define stellar regions as those surrounding individual stars, brown dwarfs, or multi-object systems, of which there are 94 within 20 light years. The size of the regions are scaled to the square root of the system mass divided by Sun's mass, times 100,000 AU. This is their region of gravitational dominance and any cometary cloud bound to them.

 Stars and brown dwarfs are bright enough to find with current equipment. In fact 22 star systems within 20 light years can be seen from a dark location on Earth without optical aid. We have basic information about planets and disks around other stars. Their parent stars tell us where to look, and the stars themselves provide data about the planets from Doppler shifts and transits.

 The number of discovered planets at all distances is growing rapidly, from none before 1988 to about 2000 by the end of 2015, and over 5000 by 2023. 59 of them are within 20 light years. Dust and gas in Disks around younger stars are visible to current telescopes, but none are within 20 light years. Two nearby star systems, epsilon Eridani and Tau Ceti, are known to have longer-lived debris disks.

Economic Uses

 Due to extreme distance, the only economic uses we see for now are science, exploration, and seeding independent colonies. More study is needed with better telescopes before any attempt to plan travel to these stars.

Exostellar Transport

 Transport between stars is covered under Phase 6A in the previous section. Travel within a given stellar region would use the same technologies as around the Sun, with modifications for available energy sources.

Exostellar Production

 As mentioned earlier, we would want to observe the nearby stars in more detail by using the Sun as a giant gravitational lens. Following that would likely be robotic probes to more closely examine whatever is found around these stars. A self-bootstrapping seed factory approach should work at other stars, since the properties of energy and matter are the same everywhere. However the details will depend on what resources are available.