# Space Transport and Engineering Methods/Combined System Overview

This section provides an overview of our chosen program. Later sections of Part 4, design studies in Part 5, and related information located elsewhere and linked will provide more details. The program concept is incomplete as of late of 2017, and readers are invited to contribute to it and improve it. Conceptual and Preliminary Design, which are the early stages of overall design and development, have not been finished. Therefore we have not selected all the preferred choices, and multiple candidates are often presented.

## Program Goals

Every program needs identifiable goals and objectives to direct the design and implementation work. Section 5.1 was an early study to develop these goals and objectives, and an initial design concept to meet them. The most compact statement of the program's goals are:
Upgrade civilization on Earth, and progressively expand to more difficult environments, including multiple regions in space.
Program objectives supporting this goal include:
* Improving Life on Earth by developing better technology to make material goods and to live sustainably from local resources.
* Expanding Material and Energy Resources by access to currently difficult Earth and space locations.
* Increasing Biosphere Security by adapting to more difficult environments, including future changes to the Earth itself, and by countering undesirable changes.
* Reducing Hazards from Space by identifying what they are, followed by developing methods to deal with them.
* Understanding the Earth Better by observing our home planet, its environment in space, and other planets and environments.
* Long Term Survival by dispersal to multiple locations and acquisition of needed new resources.
* Increasing Choice and Freedom by opening unoccupied regions to habitation and use.
* Increasing Opportunity by access to unclaimed resources and more efficient technology.
Expected benefits from this program include:
* Low cost access to space, removing a current barrier to activities there.
* Spin-off technology from attempting difficult tasks, which can then find uses elsewhere.
* Optimism for the future by demonstrating we are not in a finite, closed world. An optimistic viewpoint in turn changes how people act.
These benefits of the program accrue to civilization as a whole, although the specific projects may be funded and carried out by smaller organizations.

## Program Summary

Our current civilization significantly uses only 13.5% of the Earth's surface. The biosphere plus the human-built environment averages about 200 kg/m$^2$ if distributed evenly across this area. This is a tiny fraction of the 11.71 billion kg/m$^2$ of the Earth's total mass. The known major planets and smaller bodies of the Solar System amount to 447 times more mass than the Earth alone. In terms of thickness, our current civilization amounts to a 20 cm thick layer on the portion of the Earth we use. This is a very thin veneer compared to the bulk of the Earth. The layer thickness assumes the contents average the density of water (which living things approximately do) and were flattened and distributed evenly.
Our civilization uses about 20 TW of energy in all forms. Ignoring other energy sources, this is a small fraction of the 174,000 TW of sunlight that falls on the Earth, and a microscopic fraction of the 383 trillion TW the Sun produces. Problems like poverty and material scarcity don't stem from a lack of resources. They exist because we hardly use the vast amounts of material and energy resources that are there. Our program's approach can then be simply explained as "using more of what's already there". Of course, we want to do so responsibly, and minimize side effects to the biosphere and people's current lives.
    General Approach
Historically, people first occupied the easiest environments, and used the easiest sources of materials and energy. Our program concept is to continue the "easiest first" path, but apply modern technology towards occupying and using progressively more difficult environments on Earth, and then in space. We can leverage existing production equipment and use "smart tools" (automation, software, robotics, and AI) to efficiently make more. This starts in the easiest places, which are existing locations where people already live. Starter sets of equipment are then sent to the next harder environments, where they can use local energy and materials to grow. When they have expanded enough, they can then contribute to starting in even harder locations. People accompany the starter sets when the environment is not too difficult. In the more extreme and remote locations the equipment operates automatically or by remote control until suitable space for people is built. In this way civilization can progressively upgrade itself where people already live, expand horizontally across areas we mostly don't use yet (i.e oceans, deserts, and ice caps), and vertically down into the Earth and up into space.
We expect the program would be carried out as many separate projects, each for its own reasons. For the purpose of engineering analysis, design, and optimization, though, we will consider the program as a whole. This is similar to how airplane design has to consider the airports and traffic control system they operate with, even though the airplane manufacturers, airlines, airports, and traffic control network are all operated by different organizations. By presenting the entire program, we hope to provide a hopeful vision for the future, and inspiration for people to follow selected parts according to their interests and abilities.
Our "easiest first" approach is a progressive series of upgrades and expansions to new environments, with previous regions providing the means to open up the next ones. Existing environments continue to be occupied and used as new ones are established. Therefore we organize the program into a number of phases, with staggered starting times (Figure 4.1-1) and a sequence for which phases lead to the later ones (Figure 4.1-2). Once started, a phase continues in parallel with earlier phases, and the rest of civilization outside the program. In turn, phases are divided into smaller projects, locations, and functions, with engineered systems and subsystems which perform the functions. The parts of the program interact with each other at all levels, and with the rest of civilization, via an assortment of inputs and outputs.
The first four phases begin on Earth. These are:
* Phase 0: Research and Development
* Phase 1: Starter Projects & Network
* Phase 2: Distributed and Industrial Development
* Phase 3: Other Earth Development
The Research & Development Phase supplies necessary technology and designs to the later phases, and therefore comes first. Phases 1, 2, and 3 are distinguished by scale of operations and moderate vs difficult or extreme operating environments. Different scales and environments will lead to different specific designs, so we define phases for each. Smaller scale equipment can be used to build larger equipment, and gathered in numbers to make larger production systems, hence the sequence from starter to distributed and industrial phases. The easiest places to start are developed areas with moderate conditions, so the first three phases begin there. Phase 3 builds on that experience and therefore comes fourth, in progressively harder environments. If you wonder why four out of seven phases in a book about space systems are on Earth, keep in mind that most current space activity actually occurs on the ground. For example, six people occupy the International Space Station in orbit, but the US portion of the project alone employs about 12,000 people on Earth.
The remaining three phases are in space, which are typically harder than the most difficult locations on Earth. This is partly due to conditions like lack of breathable air, radiation, and temperature. The energy and travel times to reach various regions in space adds to their difficulty. These phases are:
* Phase 4: Orbital Development
* Phase 5: Planetary System Development
* Phase 6: Interstellar Development
Orbital development begins with regions nearest the Earth, and progresses outwards by distance to higher orbits, then to ones around the Sun from inner to outermost. Planetary System regions are tied by gravity to the Moon and major planets. They include orbits around them, on their surfaces and their moons. Finally, Interstellar regions are not tied to our Sun and Solar System. The order of Phases 4, 5, and 6 is according to distance and difficulty of reaching their locations, since equipment for a given region has to come from or through the previous ones.
Most of the major phases are divided into more specific sub-phases: 2A, 2B, 3A, 3B, etc. The entire sequence of growth and expansion is intended to be self-funding once started. Self-expanding production and other new technologies should be valuable enough to justify development on their own. Using those technologies progressively on Earth and in space can fund each later expansion.

### Phase 0: Research and Development (R&D)

Existing civilization has already accumulated a large amount of technical knowledge, designs, and equipment. There are some new items that are needed for the various program phases, so the R&D phase will do the necessary work to develop them. This includes conceptual and preliminary design, component research, detailed design, prototype fabrication, and testing. Finished items are supplied to later phases, and also to society at large when appropriate. New knowledge and technology from this phase is also contributed back to civilization as a whole. The R&D Phase is divided into multiple sub-phases, according to the later phases for which the R&D is needed. This includes for Phase 0 itself, in case unique facilities, equipment, or processes are needed to carry out the R&D work.
Seed Factories
The first major technology to be developed in Phase 0 is that of Seed Factories. We feel this concept is important enough, and its application to Earth distinct enough from space, to devote a separate book to the subject. Seed factories are systems which can bootstrap from a starter set of people and equipment to whatever size you need. They grow by making more equipment for themselves using existing tools and machines, local energy and material resources, and process and design knowledge. As new and different equipment is added to the collection, the growth rate can increase exponentially. Like any other factory system, seed factories are intended to make useful finished products. The portion of output devoted to growth vs finished products can be variable, and is determined by user needs. Where possible they take advantage of Smart Tools such as automation, software, robotics, and artificial intelligence, to leverage the work that people do. Smart tools and remote control are especially useful in dealing with difficult and extreme environments.
The current state of technology does not allow a seed factory to be fully automated or make 100% of its own parts, so it is not entirely Self Replicating. Instead, the goal is to reach a high and increasing level of self-production and automation. When expanding to a new environment or location, you bring a starter set, and it sets about using local materials and energy to make parts for new equipment. Whatever can't be found or made locally continues to be imported, but at a decreasing level as local capacity grows. The farther away and more difficult the environment, the greater the advantage of producing locally over bringing everything from elsewhere. So this approach becomes more useful as you reach farther into space. Even in developed locations on Earth, a starter set would be less expensive to buy than a full factory. So seed factories have economic justification for terrestrial use.
In already developed areas, the growing factories can also take local waste and scrap as inputs, besides using local raw materials. This provides environmental benefits. In both developed and new locations they take whatever inputs they get and convert them to finished materials, then finished parts and complete products. Items the factory cannot make efficiently will continue to be imported, and a small percentage of items will need rare materials not found locally. So even when it has reached full size, the factory is not likely to produce 100% of what it needs. All of the locations within the program, and the rest of civilization, will then make up a linked trading network, supplying each other with things they lack locally or are too hard to make.
Additional Technologies
Some other new or upgraded technologies will be useful for the program. One example is distributed production networks. Traditional factories brought people and equipment together in one place because it was the only way to efficiently organize the work. With modern communications and transport it is possible to coordinate work that is distributed across many places. This has been achieved for software development, but needs improvement for physical goods. Areas that need improvement include remote operations, and automatic process compilation to support an ever-changing set of equipment.
In space technology, current programs still do not fully incorporate already existing knowledge and hardware, such as electric propulsion. They don't yet incorporate the most basic in-space production methods, although some research is ongoing towards it. Many new ideas languish from lack of funds. So the R&D phase will follow a dual approach. First is to make the best use of what already exists in planning a coherent program. Second is to use some of the production capacity we develop on Earth to build and test equipment for the new and yet-untried ideas. Many of these ideas are listed in Parts 2 and 3 of this book. Since some of the space technology can only be tested fully in space, later parts of the R&D phase will involve locations in space.

### Phase 1: Starter Projects & Network

Early Phase 0 R&D, Phase 1, and Phase 2 all occur in moderate environments on Earth, which are the easiest places to start. We define moderate conditions for a number of environment parameters such as temperature, water supply, and air pressure. Each parameter is considered moderate where the middle 90% of people currently live, with 5% at each extreme. If any parameter is outside the moderate range, then the whole location is no longer moderate. The moderate range is intended as "typical" or "normal" conditions to design for, such that a single design should be able to operate in any part of the environment. Moderate conditions are measured by the natural exterior environment, and not the interiors of controlled production, habitation, or transport spaces.
Phase 1 begins gaining experience with bootstrapping from starter sets by building the first operational seed factory equipment. Early equipment includes conventional tools and machines that are bought or made, plus starter set machines designed in the R&D phase. Starter locations are in already developed and populated areas which can supply whatever else is needed to get started and operate. Phase 1 machines are typically small, such as for hobby crafts and home improvement type uses. This makes them affordable for individuals or small groups. The machines can be located in homes or locally-built workshops. Besides direct use for small-scale production in this phase, the experience will be useful for later phases. More remote and difficult locations will be easier to bootstrap from small starter sets, because less equipment needs to be imported.
Phase 1 also develops experience in other areas. One is creating a distributed network of individuals and small groups, with equipment in multiple places. As a coordinated effort to produce useful products and services, it can still be considered a factory or business enterprise, just not a traditional one in a single physical place. Another area is building the knowledge and skills of the people using the equipment. Small-scale production isn't taught to most people in their general education, so along with seed equipment and software, we need education and training for the users. Knowing what skills and training is needed will be useful in later phases.
We expect Phase 1 operators to mostly use their skills and machines to make items for themselves, for each other, and for their immediate community. Commercial-scale production with significant sales to the public would fall to the next phase. Since the starter sets are designed for upgrade and expansion, the evolution to the next phase can be natural and gradual. Within this phase, new network nodes and new locations can be started with partial equipment sets sent from existing ones, or purchased from outside.

### Phase 2: Distributed and Industrial Development

As more people, their skills, and equipment accumulate in a given location, they can start to sell and trade beyond their own community. They can then get most of their financial support from network operations, where in Phase 1 it was more hobby and part time levels of effort. To the extent people can support themselves, it relieves conventional risks of job insecurity and displacement by automation. In less developed regions it would mean an improved quality of life. These are useful ends in themselves, besides working towards later program goals.
The direct bootstrap approach is to use existing machines to make parts for larger machines. This scales the equipment from home and hobby, to small business, commercial, and industrial sizes. More extensive use of the equipment puts an emphasis on higher duty cycles (percentage of the time it is in operation) and service life (total hours of operation). Where light-duty equipment is adequate at a hobby level, heavy-duty equipment is preferred at industrial levels. Both scale and intensity of use require modified designs from Phase 1, and will require continuing R&D to develop. At smaller scales it is feasible to gather the full range of fproduction machines in one place, and make a wide range of products. At larger scales, the equipment and their operators become more distributed and specialized, and serve larger markets. Location designs and production flows are therefore also modified to account for the changes.
We therefore divide Phase 2 into two sub-phases based on scale and specialization. Not everyone will upgrade to larger scales and intensity of operation, so Phase 1 continues to operate, and there would be a mix of small, medium, and large equipment. Phase 2 locations are in the same moderate environments as Phase 1, with developed and populated areas nearby.
    Phase 2A: Distributed Locations - This covers locations that move beyond hobby and home improvement levels of effort within the network, to small business and commercial levels capable of providing most of an individual's financial support, and a wider total range of products and services provided to people outside the network.
    Phase 2B: Industrial Locations - These serve larger and more widespread markets at the most efficient levels of size and specialization. This scale may require outside funding for land and equipment, where earlier phases could be self-financed through internal growth. This is because buying and developing an industrial-scale site is hard to do in small increments. Because sources of supply and customers are more widespread, transport capacity becomes more important. Outside market forces also become more important than the internal needs of the community. One way to deal with market forces is distributed ownership across multiple industries, so that people's work and equipment can be reassigned as needed.

### Phase 3: Other Earth Development

Difficult and extreme regions on Earth are those which are more than 10 and 20% beyond moderate conditions in any of a number environment and development parameters. See Section 5.2 Environment Ranges for details on the parameters. These areas include remote, unpopulated, and undeveloped areas on the surface, such as oceans, deserts, and ice caps. They also include areas away from the surface, such as deep underground below existing cities, or at higher altitudes. These may be physically close to moderate surface locations, but harder to build in.
The more difficult and extreme the conditions, the more that designs have to be modified to accommodate them. This is accomplished by either modifying the working equipment, or artificially moderating the local operating environment to a suitable range. Because of the scope of design modifications needed, we divide this phase into two sub-phases, based on the amounts required. Because conditions can vary in many ways from moderate ones, we expect a number of custom designs will be needed. These locations are generally undeveloped and unpopulated. So starter sets and other equipment can't be obtained locally, and would be delivered from previous locations. They would not typically be small scale, because local operators don't have other jobs to support themselves, or the extra space to house them. The higher costs of transport, and supporting on-site people and remote operations, also tends to make small scale equipment uneconomic.
This major phase allows us to extend civilization to the 6/7ths of the Earth's surface we don't yet significantly use, and vertically both down into the ground and oceans, and up to higher altitudes. The world's population is expected to continue growing in the 21st century. People in currently less-developed areas also want to reach higher levels of economic development. Expansion to new areas will to some degree be needed to satisfy all their needs. This is not so much a need for personal space, since on-going urbanization concentrates people in compact clusters. Rather, it is to access increased energy and material resources. An example project for these areas is to establish greenhouses and water supply systems in deserts to increase food supplies. Automation and remote control allows such locations to operate, even if a lot of people don't want to live there. The two sub-phases are:
    Phase 3A: Difficult Earth Locations - These are defined as having at least one parameter 10% or more beyond the moderate range, measured linearly or logarithmically depending on the parameter. The parameters are measured before local development and upgrade. For example, reaching deep underground is difficult before suitable tunnels and shafts are built, but not afterwards. Difficult temperatures are average winter lows below -18C or average summer highs above 42C, such as arctic or hot desert areas. Drier deserts and wet rainforests have difficult levels of water supply - too little or too much. Altitudes above 2750 meters begin to cause problems for some people, and soil strength below 0.19 MPa or ground/water pressure above 2.5 MPa are difficult to build for. Energy supply, primarily from wind and solar, below 125 W/m$^2$ makes all activities which need power difficult. Locations well below the surface are cut off from these sources. Gravity is nearly constant on Earth, and most places are below 17 mSv/year in background radiation, and are not difficult in these parameters. Communications round-trip (ping time) over 100 ms and normal one-way travel time for people that takes over 2.5 days are considered difficult. Average residence times below 5 years and cargo transport energy above 2.85 MJ/kg impose extra transport burdens from staff turnover and difficulty of outside supply.
    Phase 3B: Extreme Earth Locations - Extreme locations use the same parameters, but are at least 20% beyond the moderate range, up to the limits of existing technology. So average daily lows below -23C or highs above 47C are extreme, and only found in severe climates, at high altitude, or deep underground. Water supply below 0.12 or above 3.8 meters/year, and air pressure below 70 kPa or above 120 kPa (+5500m and -1600m altitude) are also extreme conditions. Soil strength below 0.12 MPa, which includes water surface of no strength, are extreme conditions to build on. Therefore all of the ocean surface where it is too deep to build from the sea floor is considered extreme. Ground and water pressure above 3 MPa require extra structural support, and are found at depths below 300 meters in water and 120 meters in rock. Gravity is never extreme on Earth, but some high background radiation areas and high altitudes over the magnetic poles exceed the 21 mSv/year level and are considered extreme. Ping time over 125 ms occurs if modern communications are absent, and travel times over 3 days if conventional transport isn't available. These fall into the extreme range, as are residence times below 3 years 4 months, and cargo transport energy above 3.5 MJ/kg. Determined mining should be able to reach depths of 9.5 km in continental crust and 7 km in oceanic crust in addition to water depth. Counting the oceans, the equivalent of 4.6 billion km$^3$ of total resources should be accessible.

### Phase 4: Orbital Development

We already explore and use space beyond the Earth to some degree. That use is limited by the difficulty and expense of lifting everything needed up the Earth's deep gravity well. We get around this problem by exploiting the energy and materials already in the Phase 4 regions to make things locally. This allows much fuller development of the regions and expansion of civilization. Production capacity from the previous phases is used to build things like rockets and launch sites, which can deliver starter sets and other equipment to orbit. These bootstrap local production, habitation, transport, and services in a progression of locations, starting near Earth, then moving into "open space", away from strong gravity wells. These locations share high levels or full-time sunlight for energy, low gravity for ease of moving large masses, and vacuum which can enable certain production methods. These shared conditions lead to shared designs, so they are grouped into one major phase.
With greater distances from Earth and the Sun there are increasing transportation needs, and thermal, power, and other design changes needed. This leads us to identify six sub-phases by region. Each of these leads to the next in sequence, with products from one phase used to help deliver and set up locations in the next. Orbital production would first support existing space industry, which amounts to nearly 1500 active satellites and $340 billion in economic activity as of 2016. As bootstrapped production lowers costs, current markets should expand, and new one become economic. So, like previous phases, this phase should be self-supporting once started.
    Phase 4A: Low Orbit Development - We define Low Earth Orbits as extending from 160 to an average of 2700 km above the surface. The lower bound is set by significant atmospheric drag, which prevents stable orbits. The upper bound is half the potential energy from the lowest orbit to Earth escape. It is stated as an average altitude, because elliptical orbits are possible, which vary constantly in altitude, but not in total energy. Most low orbits are in the Earth's shadow from 22-40% of the time, which lowers available solar power, and typically requires power storage for the time in shadow. Temperatures and lighting are moderated by the nearby Earth, and communications and travel times are relatively short. The natural environment includes the inner part of the Van Allen radiation belts, and a modest flux of meteoroids. Material resources include the upper edge of the Earth's atmosphere, and artificial space debris. Other materials would have to be imported from elsewhere.
    Phase 4B: High Orbit Development - High Earth Orbits extend from 2700 km average altitude to the limit of the Earth's gravitational dominance at about 1.5 million km. Although this is a large range in distance, it only represents the upper 25% of energy between the Earth's surface and escape. It excludes distances within 35,000 km of the Moon and the Moon itself, which are assigned to Phase 5A below. High orbits are in sunlight 78 to 100% of the time, and temperature is mostly governed by the Sun. Communications and travel times at the outermost edge can extend to 10 seconds ping time and 7 months transit by the most efficient route. Like lower orbits, the natural environment includes high radiation levels from the remainder of the Van Allen belts, and, outside the magnetosphere, from solar and galactic radiation sources. Meteoroid flux is similarly modest, as it is for most of the rest of the Solar system. Material resources in place include a smaller amount of artificial debris, but high orbits are fairly accessible to the Moon and Near Earth Asteroids. Materials can be delivered from these locations, and then the high solar flux used for local production.
    Phase 4C: Inner Interplanetary Development - This region includes orbits from as close to the Sun as technically possible to an average of 1.8 AU, where the Main Asteroid Belt starts. It excludes the four major planets Mercury, Venus, Earth, and Mars and the gravitationally bound regions around them. Inner interplanetary orbits are in sunlight 100% of the time, and solar flux varies from 31% to many times that near Earth. Even the lowest levels match the best places on Earth, because there is no night or atmospheric absorption to reduce it. Temperatures vary with amount of solar flux, requiring sunshields or insulation to moderate them for people and equipment. Communications time is up to 1 hour round-trip across this region, and travel time can be several years by lowest energy transfer orbit. There are over 17,000 known objects in this region as of late 2017, growing about 1500/year. The largest member alone has an estimated mass of 17 trillion tons. So material and energy resources are widely available for production and other purposes.
    Phase 4D: Main Belt and Trojan Development - This region includes orbits averaging from 1.8 to 5.2 AU from the Sun, except for the part within 20 million km of Jupiter. Conditions are similar to the previous phase except that solar flux varies from 31 to 3.7% of that near Earth. At the outer reaches, solar reflectors or other power sources such as nuclear may be needed to maintain temperature and supply power. Communications times can range up to 2.88 hours in the worst case, and travel can take 12 years by the most efficient route. Material resources include over 700,000 known objects in the Main Belt, Hilda, and Jupiter Trojan groups. Their combined mass is on the order of 3 billion billion tons, all of which is accessible to sufficiently determined mining operations. These materials can be sent slowly but efficiently to inner regions by means of electric propulsion and gravity assists from the major planets. The farther part of the region contains large amounts of water ice and other volatile compounds because of the low temperatures.
    Phase 4E: Outer Interplanetary Development - This region includes orbits from 5.2 to 50 AU from the Sun, except for the regions around Saturn, Uranus, and Neptune. Solar flux is quite low in this region, from 3.7 to 0.04% of that near Earth. Nuclear power sources or very large and lightweight solar reflectors will be needed to supply power and keep warm. Without those, objects will naturally be at temperatures of -56 to -200 C, depending on color. Round-trip communications time ranges up to 1.15 days, and travel times would be up to 350 years by the most efficient orbits. This is too long to make economic sense, so actual travel times will depend on the availability of faster transport methods. There are about 1750 known objects in the Kuiper Belt beyond Neptune (30-50 AU), and another 340 Centaurs and short-period comets, whose orbits cross one of the gas giants. This includes Pluto and several other dwarf planets, with a total mass in this region of 4-10% of the Earth's. There are likely many more objects in the region which are too small to find at present. The region is rich in water and frozen gases due to the low temperatures.
    Phase 4F: Scattered, Hills, and Oort Development - The final orbital region is the vast one extending from 50 to 100,000 AU average distance from the Sun. This region shares extremely cold temperatures and being close to Solar escape energy. We divide it into three parts by distance - The Scattered Disk from 50 to 2000 AU, Hills Cloud from 2000 to 10,000 AU, and Oort Cloud from 10,000 to 100,000 AU. The outer limit is where the Sun's gravitational dominance ends. Our ability to detect objects in this region is poor at present. This is due to distance, and lack of sunlight to reflect back to us. Only about 335 objects in fixed orbits are known, and a small number of long-period comets. We expect many thousands more await discovery, including a possible planet the size of Neptune. Total mass in this region is not known, but may be a large multiple of the Earth's. Travel, communications, and powering of equipment would be very difficult with current technology. So significant development will await future improvements in those areas.

### Phase 5: Planetary System Development

Planetary system locations differ from orbital ones in being tied to relatively large gravity wells, requiring additional transport capacity to traverse. They can also experience shadowing or night when close to or on the surface, and higher radiation levels from trapped particle belts. The surfaces of large bodies have significant gravity levels, and sometimes an atmosphere. All of these conditions are different from those in the open space of Phase 4, leading to a different phase with different designs for them. The various planetary systems also differ from each other, requiring designs to accommodate each. So we provide five sub-phases to cover the range of such locations. The sub-phases are in approximate order of difficulty. The start of sub-phases for Orbital and Planetary development overlap in time. Each planetary one starts after the orbital regions which must be traversed to reach them.
    Phase 5A: Lunar Development - The Lunar region includes the Moon itself, and orbits within 35,000 km on average from the Moon's center. The Moon is relatively close in physical distance to Earth, but reaching the surface requires significant additional energy due to it's gravity well. Therefore it comes after Phase 4B: High Orbit in terms of difficulty. Communications and travel times are relatively short, less than for some parts of High Orbit. Available sunlight per area of the Lunar surface is 50% of that for high orbit on the equator, and less at higher latitudes. Availability can reach 99% for the highest circum-lunar orbits. Average temperatures are similar to that on Earth, but exposed areas can vary hundreds of degrees between light and dark. Determined mining on the Moon should be able to reach depths of 50 km before rock pressure makes it unreasonably difficult. This makes 2 billion cubic km of resources potentially available. Because of its origin and history, the Moon is depleted in Volatiles compared to even nearby asteroids. These are elements and compounds with relatively low boiling points, such as water and atmosphere found on Earth. Conversely, Lunar Geology indicates a high percentage of metallic oxides, making it a good source of oxygen and various metals.
    Phase 5B: Mars Development - The Mars region includes the planet itself, and orbits up to 340,000 km in average distance from its center. This includes the natural moons Phobos and Deimos. The orbit of Mars is eccentric, so solar flux varies from 36 to 52.5% of the near-Earth reference amount. Surface gravity on Mars varies from 3.68 to 3.74 m/s$^2$ (37.5% of Earth), and atmospheric pressure varies from 30 to 1155 Pascals (0.03-1.14% of Earth). Mars locations would follow phase 4C: Inner Interplanetary, since you must travel through interplanetary space to reach Mars. Determined mining should be able reach depths of about 25 km, providing 3.6 billion cubic km of accessible resources, nearly double than from the Moon. Mars retains significant water, and has a quite varied geology.
    Phase 5C: Venus and Mercury Development - These regions include the two planets, and orbits averaging less than 600,000 and 100,000 km from their centers. A relative lack of known nearby asteroids or moons, higher delta-V to reach their orbits and land on them, and extremely hot or high pressure conditions places these locations after Mars. Their advantage consists of 1.9 and 4.6-10.6 times more solar flux, providing ample energy to extract and process resources. The lack of known asteroids in this region may be due to the short orbit times, which allow frequent planet flybys. A given asteroid will then be removed by either hitting a planet, shifting the orbit outwards, or shifting it so close to the Sun it vaporizes. New objects are supplied by gravitational changes from farther orbits. The lack may be partly due to the difficulty of finding small objects when looking towards the Sun. If the planets themselves and nearby asteroids prove insufficient or the wrong composition, it can be made up by imports from the better supplied outer regions.
    Phase 5D: Jupiter System Development - The Jupiter system includes the largest planet, 69 known moons, four of which are very large, and orbits within 20 million km of the planet's center. The larger moons are useful for gravity assists, making travel between locations easier, but the great mass of Jupiter makes reaching the planet itself very hard. Development of Jupiter would logically follow Phase 4D: Main Belt and Trojan. Jupiter sits between it's Trojan clusters, and the outermost moons are really loosely captured asteroids, making it an easy next step. Progressing inwards needs more transport energy, and you encounter lethal radiation levels, requiring lots of shielding for people and equipment. The large moons represent many billions of cubic km of resources, which would eventually make them attractive sources. However solar flux of 3.3-4.1% of Earth's is a challenge to supply enough power to make use of those resources.
    Phase 5E: Outer Gas Giant Development - This phase includes Saturn, Uranus, and Neptune, and the surrounding regions within 20, 12, and 12 million km respectively. It includes 103 known moons, a number of which are large, and three ring systems, one of which is famously prominent. Solar flux is 1%, 1/4%, and 1/9% of Earth's, respectively, making alternate energy sources very attractive. These locations follow Phase 4E: Outer Interplanetary, as you must travel through that region to reach the three planets and their surroundings. This phase is far enough in distance and needed technology that a significant amount of research and development is needed before it can be used.

### Phase 6: Interstellar Development

The last major phase includes locations which are not tied to the Sun's gravity well. This includes open interstellar space not tied to a specific star, and the regions around other stellar systems. There is no reason to stop the expansion of civilization at the borders of our Solar System, assuming we have the necessary technology and it is economically reasonable. However, at present we don't have full knowledge of what planetary systems exist around even the nearest stars, and transport technology to reach them in reasonable time is currently speculative. We include this phase as a long-range program goal, but with the understanding that most of the details will have to wait. We divide this phase into three sub-phases, to account for the different environments and activities in nearby interstellar space and exostellar systems, and for farther reaches of the Milky Way.
    Phase 6A: Nearby Interstellar Development - This region begins 100,000 AU from the Sun, where it's gravity is no longer dominant. For design purposes we set an arbitrary limit of 20 light-years from the Sun. If we can reach that distance, and restock/rebuild our equipment, then later projects can travel further in increments of 20 light years, but not require new designs. The interstellar region excludes the stars within 20 light-years and their respective regions of gravitational dominance. They are assigned to Phase 6B since they have more in common with previous phases closer to the Sun than the spaces between stars. The volume of this region therefore resembles the solid portion of Swiss cheese, with scattered holes that are not included. Contents of this region are poorly known as of 2017, but very low density. It includes the interstellar medium of gas, dust, particles, and radiation. It likely includes a population of objects larger than dust but smaller than stars, which are so far mainly undetected.
    Phase 6B: Nearby Exostellar Development - There are currently about 105 known Stellar and Brown Dwarf star systems within 20 light years. We know much more about the stars than what orbits them or the spaces in between, because stars are bright and we can more easily collect information from their light. Each star has a region of gravitational dominance over the Galaxy as a whole and other nearby objects. This is estimated to be 100,000 AU times the square root of the system mass in units of our Sun's mass. The stars are all in motion relative to each other, so the population within 20 light-years changes on average every 1150 years. There are about two dozen known planets in this region, and two have circumstellar disks, but this data is incomplete due to the difficulty in detecting planets. Design for these locations must await better information, and a lot of new technology development.
    Phase 6C: Farther Interstellar Development - Our last sub-phase is a place-holder to cover the remainder of the accessible Universe. It begins 20 light-years from the Sun and extends as far as transport methods make it possible to reach. Since current and near-term methods are far from able to reach such distances, work on this sub-phase beyond transportation improvements is reserved to some point in the future.

## Program Structure

To make a large and complex program comprehensible, we divide it into multiple levels of detail, with each level dividing a given part into a reasonable number of smaller parts. At the most detailed level, individual program elements are small and simple enough to be designed and implemented, without further division. For this example of a complex program we will not carry it to that level of detail. It would first require completing conceptual and preliminary design, which isn't done yet, and there isn't space in this wikibook to include all the information. Instead, we will present the top several levels and the process of defining their elements, with the understanding that future work can use similar processes at the lower levels.

### Level 1: Program

The top level is our program as a whole. It is here that overall goals and objectives are defined, and top level interactions occur with the rest of civilization. Decisions are also made to implement parts or all of the program vs. staying with what is already in progress and planned. Change takes more work than staying with what already exists. So a new program has to be sufficiently better to motivate people to change. That requires developing the needed ideas and technology, and educating people about why they are better. We refer to what already exists as the Existing Baseline. For example, in space launch that would include rockets that are already in operation, and new ones already funded and in development. For factory production it would include currently operating factories, and the state of the art for building new ones. Our program is not yet developed enough to recommend implementing it, but we think it has great potential. This is what has motivated our work to date, and we hope to continue it until we can make a recommendation for or against it.

### Level 2: Phases

Level 2 of the program includes the major program phases and sub-phases described above, and in the later sections of Part 4. These phases inherit parts of the top level goals and objectives, such that all the phases together meet all of them. Earlier phases and their parts may only meet some of the goals, or at lower levels of performance, with the intent to upgrade and expand the coverage later on. Part of the early design process is to specify what goals and performance levels each phase will accomplish, and timing for when they reach them. Since the phases are covered in more detail elsewhere, we won't duplicate that information here.

### Level 3: Projects

Each phase can include one or more projects. These projects are intended to accomplish a task or meet a goal. For example, the Seed Factory Project, which has already been started, is intended to design and test prototype systems to prove out ideas for self-expanding production. This project is part of Phase 0: R&D. A hypothetical "Floating Cities Project" would be part of Phase 3, due to the difficult or extreme environment of the oceans.

### Level 4: Locations

The program is aimed at upgrading and expanding civilization for the reasons listed in the Program Goals section above. The general approach is to build up a given location, adding functional elements that allow internal growth and useful outputs. Each location helps support itself, interacts with previous locations, and with the rest of civilization. When enough capacity has built up at current locations, they can deliver starter elements to a new location. The starter set then repeats the cycle of growth and useful outputs. Parts and materials are delivered from previous locations for whatever cannot yet be made locally. Locations are defined by ease of internal local transport for people and bulk goods. An example is a metropolitan area around a city, where travel times are a couple of hours or less between the various parts, and a good road network exists. Transport between locations will happen, but the increased time and cost will make it less frequent, and preferably for high value, low mass items. So you may ship a computer to a distant location, but you prefer not to send a truckload of gravel that far.
Locations in undeveloped, difficult, or extreme environments, and in space, may be much smaller than a city at first. This is due to lack of transport systems like roads and airports, and large distances to the next location. In developed regions, the overall size of a program location is typically that of a metropolitan area, but does not include all the contents of that area. It only involves program-specific people and equipment located there. They interact with the surrounding non-program region, and other program locations.

### Level 5: Functions

The next level below a single location are the functions performed there. All of civilization shares common functions, such as protection from bad weather, supplying food and drink, fabricating parts, and assembling them into useful items. Eating utensils and CNC laser cutters, for example, can be more or less the same from one location to the next. So we don't have to design unique elements for every location. Instead, we can identify the functions that need to be performed there, then copy existing designs or modify them as needed to satisfy the needs. Each function, like cutting parts from stock material, has inputs like electricity, and instructions on what part to make, and outputs like the finished parts and unused scrap. These inputs and outputs connect functions to each other, and to outside the program boundary. The functions and their connections can be displayed in various ways, such as the example diagram in Figure 4.1-3.
Because civilization shares common functions and these functions share common connections between them, we can define a Reference Architecture that applies to existing elements of current civilization, and new elements of our program. This makes it easier to compare what already exists to what is new, and saves us from having to define the organization of new locations each time. A given location may only include a subset of the common functions, especially when it is new. Locations can evolve over time, adding new functions. The program as a whole also evolves over time, adding new functions and upgrading existing ones.

### Further Levels

Functions can be subdivided into more detailed ones, and then systems and specific elements designed to perform those functions. This work falls into the various fields of engineering. For space systems, some of the methods and concepts are described in earlier parts of this book. For other kinds systems, we refer the reader to the enormous range of technical literature for them. For reasons of space and time, we will not cover this level of detail in our current work, but we will note it is eventually needed to implement actual projects.