Section 4.2: Phase 0 - Research & Development
The main program goals are upgrading civilization on Earth, and expanding to more difficult environments, including space. To accomplish these goals, some new technologies and methods are needed, which are incorporated into suitable designs for the intended locations. In particular for space locations, there has been a lack of production and habitation capacity, with the main focus so far being on transport. This imbalance exists to a lesser degree in difficult Earth environments. For example, many ships (transport) cross the oceans, but relatively few things are produced there, and few people inhabit the seas. Phase 0 is therefore included in the program to supply what's needed for the later phases, and consciously correct unbalanced development where possible. The major goals of Phase 0 can then be stated as:
- (1) Identify systems and elements covering the full range of production, habitation, and transport functions.
- (2) Supply needed new technologies and methods, in the form of tested and ready to use elements.
- (3) Supply detailed designs for equipment and locations, incorporating both existing and new elements.
The program as a whole is complex. Systems engineering methods were developed to handle such complexity, so we will use them to develop this and later phases. Other engineering methods can also be used where appropriate, but the systems approach is especially useful across whole programs. This includes their interactions with the world outside the program, and the constituent parts of a program with each other. Part of the systems process is to break down complexity into smaller parts, which are then more comprehensible and easier to design. We have already started this in Section 4.1 by identifying a sequence of phases and sub-phases according to scale, type of environment, and distance. A given set of locations within a sub-phase can then share similar designs, and to a lesser degree with those of the major phase and program as a whole.
Civilization as a whole has common elements across all of it. For example, people need protection from the environment and food to eat no matter where they are. Heat-treating alloy steel can use the same process anywhere you need to do it. We can therefore define a reference architecture for these common elements of civilization, and apply it to organize the tasks of upgrade and expansion. Many existing parts of civilization and component technologies are good enough as-is for the upgrades and expansions we would like to do. In those cases, we don't have to change them, just use them. Other items are deficient or undeveloped. As we identify them, we can rank them by parameters like benefit ratio, cost, difficulty, probability of success, and time to complete. Then we can add them to our R&D plans in the best sequence. New technology we develop is used internally in the program, and also supplied as a benefit to civilization at large to use elsewhere.
The R&D work can be divided into a general part that applies across the whole program, and sub-phases covering work for specific environments and locations. The sub-phases and tasks are detailed further below. Limits on current knowledge and project resources mean we cannot do all the R&D work in advance or all at once. Therefore this phase is expected to continue in parallel with later phases for as long as the program continues. Early phase production products and services can be used to support later R&D. Field experience from earlier phases can also be fed back to improve later designs. We also expect progress across civilization in other technologies, so a given design may no longer be optimal and require upgrades.
The research and development process is similar across all phases and subphases. We give the component tasks a consistent numbering system so they may be coordinated and compared across the program:
Task 0: Coordinate R&D
- 0.1: Coordinate R&D External Flows
- 0.2: Coordinate R&D Tasking
- 0.3: Coordinate R&D Planning and Scheduling
- 0.4: Coordinate R&D Analyses
Task 1: Conceptual Design
- 1.1: Explore New Concepts
- 1.2: Develop Reference Architecture
- 1.3: Identify Requirements & Measures
- 1.4: Perform Functional Analyses
- 1.5: Allocate Requirements
- 1.6: Model Alternatives & Systems
- 1.7: Optimize & Trade-Off Alternatives
- 1.8: Synthesize & Document Design
Task 2: Preliminary Design
- (Follows same steps as conceptual design, but at greater level of detail)
Task 3: Build R&D Locations
Task 4: Develop New Technology
Task 5: Build Prototype Elements
Task 6: Test Prototypes
Task 7: Design Location Details
Sub-Phase Identification - Plain "Phase 0" with no additional letter identifies general R&D which applies across the whole program. When the work is specific to a single phase, a letter is added, such as 0A or 0B. When it applies to two or more phases the R&D work is identified with all applicable sub-phase letters, thus 0CD or 0G-L. Since some R&D locations are themselves subject to new technology and design, the first sub-phase applies to itself. The sub-phases and some of the identified R&D topics are listed below. The topics are sorted by functional tasks, rather than time order, since R&D sequence and schedule planning is a much later step.
We have identified Seed Factories as a general new technology for use by existing civilization locations and all new ones. Other general technologies for general use include remote-controlled and automated production. Manufacturing in general, and automation in particular, already gets a lot of engineering effort, so we will not duplicate it. The program efforts will focus on the unique aspects of self-expanding production, and integrating other technologies to leverage establishing new locations and upgrading existing ones. We can refer to the combined work as "Advanced Manufacturing". Enough work has gone into the seed factories idea to start a second wikibook on the subject. We provide a short introduction here, and refer you to the other book for detailed information.
Seed Factories Introduction - All factories produce products, and some factories produce the same kind of products they use themselves. For example, steel plants typically use some steel in their own construction. Self-expanding factories are specifically designed to use their own output to grow, and a seed factory is an optimized starter set of equipment, plus plans and instructions for a chain of expansions to some desired mature state. Using tools to make more tools is not a new idea, in fact it is nearly as old as toolmaking itself. What is new is optimizing a small starter set for this process, applying modern computer software, automation, and robotics to the task, and applying several ways to increase factory output:
- Adding identical copies of the starter machines,
- Producing larger versions or extensions to the starter set, and
- Producing different machines that can do different tasks and so expand the range of possible outputs.
This technology should be worth developing on Earth for it's own sake. It should make setting up new factories cheaper, especially in remote or difficult locations. With an emphasis on self-growth, they may also achieve high rates of return. Once developed on Earth, industrial-scale matured factories can build the launch sites and rocket factories to reach space. New seeds are then delivered to space locations, and the expansion process continued. The experience gained on Earth, and the leverage from a series of self-expanding factories, multiplies the savings on future space projects, making them affordable.
Phase 0A - R&D for Phase 0 R&D Locations
Even when no new equipment or technology is needed for itself, research and development needs locations for offices, laboratories, prototype fabrication, and testing for later phase equipment. We therefore apply the R&D process above to design and build these locations. When new and unique items are needed, such as a special test chamber, they are developed and built the same way as equipment for later phases.
Phase 0B: R&D for Phase 1 Starter & Network Locations
Distributed Production Networks - Traditional factories and large offices bring equipment and people together in one place because it was the only way to efficiently organize the work. Modern communications and transport networks relieve the requirement to be in one physical place, and allows coordination of a distributed network in many places. The control of production machinery can be a mix of a on-site humans, remote control by humans, and automatic control by computers and software. Since all the people don't have to be nearby, you can operate in undeveloped, hostile, or expensive locations more easily, and with less of an environmental footprint. Human operators can split and re-assign their work between locations as needed if they work remotely. Likely some machines and jobs will still end up grouped together in common locations, we are merely removing the requirement that they all have to be. Parts of the needed technology already exist, so the R&D tasks for this phase are to improve or fill in the parts that are not, and combine them into flexible distributed networks. The flexibility is needed because the program intends to constantly add new locations, and seed factory technology will grow existing ones. So we cannot use static networks.
In this phase the goal is to reach a sufficient capability to connect and operate hobby and home improvement level equipment in fairly close proximity, like a single metropolitan area. Later phases would incorporate remote operations such as on the Moon from Earth, or Mars from Phobos, and may therefore require upgrades to the technology. Space is a particularly undeveloped, hostile, and expensive location. So when you optimize your operations you will want to minimize the on-site humans, and maximize remote control, automation, and robotics. So at first there will be a strong incentive for the upgrades. As factories, habitats, and transportation systems are built for the later phases, the optimum will shift towards having more humans on-site because they can be supported locally more easily. Having gained experience with the distributed approach on Earth, moving to space will not be something entirely new, but rather an extension of what you already know how to do.
Phase 0C - R&D for Phase 2A Distributed Locations
R&D for this sub-phase involves design of more specialized and larger machines than Phase 1. These are used for small business and commercial activities, therefore would have higher duty cycles and longer operating lives. Besides design for these conditions, another R&D topic is the best growth paths from the previous phase, and expansion across a wider range of industry categories. A third R&D area is the grouping of varied size equipment in terms of more specialized and distributed sites across a location, and linkages between locations. All of these R&D areas continue in the next sub-phase to the industrial scale, which is the largest class.
Phase 0D - R&D for Phase 2B Industrial Locations
- 3. Industrial Transport
Launch to Low Orbits - This is placed in Phase 2B because traditional rocket factories and launch sites are industrial-scale facilities on Earth. Locations for Phases 4-6 are in space, but still interact with civilization on Earth, so there will be a continuing need for launch from Earth to orbit. Obviously space programs already exist, and many satellites are in orbit, but their cost is high. Partly this is due to the transport cost itself, and partly due to lack of production in space. This forces all equipment and supplies to come from Earth. In-space production is addressed in the later phases, while this topic covers launch cost.
In the earliest stages of the program, launch needs will be small, and therefore using existing launch systems will be the less expensive route. As program traffic increases, the advantage of new and more efficient systems will grow. The R&D in this sub-phase will then cover such new systems, beyond those already in development elsewhere. Sections 4.3, 4.5, and 4.6 present some early concepts for this R&D work. In section 4.3 - Startup Launcher we consider a small, 3 stage, fully re-used conventional rocket and some other alternatives for the "build our own" option. The design is not complete enough to decide between make or buy yet. The intent is when traffic is sufficient, the start-up transportation will be augmented or replaced with larger, more efficient, and specialized launchers. The initial cargo may consist of assembly robots and parts for an initial orbital platform. If we are building our own launcher we want to make it as small as practical to keep the design and construction cost low.
Upgraded Transport to Low Orbit - The program will add upgraded transport when there is sufficient traffic to justify the capital cost. Again, there is always the option to use transport from outside the program, but we consider various internal alternatives using our self-production capacity. On Earth we use different transport systems for bulk cargo than for passengers for cost and safety reasons. One alternative is to specialize our space transport elements for the same reasons. Section 4.5 - Hypervelocity Launcher presents a high acceleration gun for launching bulk cargo such as propellants or structural parts. Delicate cargo and humans would travel by other methods. The launcher gives the cargo a large starting velocity, so it substitutes for part of the rocket stages. In theory it should lower cost because a fixed gun can be designed to fire many times, and is made from industrial pipeline quality parts, which are much cheaper than aerospace grade parts.
Section 4.6 - Low G Transport looks at methods for transporting humans and cargo which cannot withstand the high acceleration of the hypervelocity launcher. The choice of which to use depends on results of more detailed design and what other launchers reach completion. Some candidates if we build our own systems are a combined air-breathing/rocket system, or a gas accelerator similar to the hypervelocity launcher, but lower g level, followed by air breathing/rocket stages. Separate stages will be easier to develop, modify and upgrade than a single integrated vehicle, although there will be a penalty in operations cost. A single integrated vehicle can be developed later once traffic will support the more complex design.
Phase 0E - R&D for Phase 3A Difficult Earth Locations
Difficult and Extreme locations involve all the sizes from small to large that were developed for Phases 1 and 2, but in a different environment. Therefore the existing designs will sometimes need modifications, and in other cases unique designs will be needed. The effort to set up in remote or hostile conditions will tend to make personal hobby or home scale equipment less likely, and the emphasis shift to larger sizes. Example difficult environments include very cold and hot regions, deserts and rain forests, altitudes above 2750 m, weak soils, water and ground depths of 250 and 100 meters respectively, areas of low energy resource or high natural radiation, high communication and travel time, low stay times, and high transport energy, or combinations of these conditions. Each may require R&D to accommodate the particular circumstances.
Phase 0F - R&D for Phase 3B Extreme Earth Locations
Extreme locations are an extension of difficult ones, but farther from moderate conditions up to the limits of technology. R&D would be needed to push technical limits beyond the state of the art. An example would be hard rock mining more than 5 km below the surface, well below the deepest current mines. Some example extreme environments include very cold conditions in parts of Antarctica, The open ocean surface, which has zero ground strength, great depths underwater or underground, and the most remote and inaccessible surface locations.
Phase 0G - R&D for Phase 4A Low Orbit Locations
Low Earth Orbit already hosts many satellites, and as of the start of 2017, two space stations with a total crew of eight. However it lacks significant production capacity, aside from assembly of pre-made elements at the stations, eight people is only one billionth of the Earth's population, and no transport systems are based in Low orbit. What transport exists is all based on Earth. So while we have a foothold in low orbit, civilization can't be said to have expanded to this region. The R&D for this sub-phase is then aimed at full use of low orbits, beyond current programs and activities. So far we have identified the following:
- 1. Low Orbit Production
1.3. Extract Materials - Low orbit has two sources of materials besides those brought from Earth. The first is the upper fringes of the atmosphere, which can be collected by a compression scoop. The second is dead space hardware and artificial debris. Some of the gathered gases can be used as propellant for collecting the space debris, since they are in widely scattered orbits. The space debris at the least is a hazard, and removal is a benefit to other space activities. But it consists of aerospace-grade parts and materials, some of which may still be functional. Salvage and recycling of these items would save having to launch comparable items from Earth. R&D is required to prove the gas mining, collection, and reuse of old hardware is practical. It would also provide some experience for later mining and production beyond low orbit.
1.4 Materials Processing & 1.5 Parts Fabrication - Very little of either of these has been done in orbit and in zero gravity. Extensive experiments and prototyping are needed to find out which terrestrial methods can be used, how they may need to be modified, and what new methods can be used in the unique orbital conditions.
1.7 Low Orbit Assembly - The design of transport systems typically is much more expensive than a single use of them. Therefore a number of deliveries on a smaller launch system is preferred on cost to a single delivery on a very large one. This in turn drives a need for assembly of larger elements in orbit. Section 4.4 - Orbital Assembly gives one approach, using an assembly platform in low orbit. At first, the platform assembles pre-made components launched from Earth. As other production elements get added, it later shifts to assembling a mix of Earth and locally made items. The first task of the assembly platform would be to bootstrap it's own construction. The platform is then used to assemble larger payloads, and then then later build seed elements and vehicles for new locations. Humans are kept to a minimum in the early stages because of cost. The assembly robots start out mostly controlled from the ground. Some experience already exists with orbital assembly of space stations, and similar maintenance and repair tasks for the Hubble Space Telescope. The R&D tasks here are whatever improvements are needed beyond these levels.
- 2. Low Orbit Habitation
Variable Gravity Research Facility - The near Earth environment, like most of the Universe, is hostile to human life. Therefore habitats have to be designed specifically to create the proper conditions. One major alternative for orbital habitats is gravity levels. Humans need some level of gravity for long term health, but exactly how much and for how long is not known yet. Some production methods work better with acceleration, and some agriculture may also turn out to work best with gravity. A VGRF type facility is needed to assess what gravity levels are needed for what purpose, so that later designs can use the proper levels.
Habitat Growth and Upgrade - Habitats will generally start small and grow over time. So another research area is the best growth paths for the them: in physical size, from possibly zero gee to some gee level, from open food and air cycles to closed life support, and from hardware supplied from Earth to local production. The design of the habitats is likely to be complex, and we can only lay out these open questions as a starting point for further work.
- 3. Low Orbit Transport
This category covers transport that operates within low orbits, and reaches farther destinations. Transport to low orbit is covered under Industrial or Difficult Earth Locations, because that is where they are built and start from.
Electric Propulsion - Ion and plasma engines have about 5-10 times the fuel efficiency of conventional rockets, and have already seen some operational use. Section 4.7 - Electric Thrusters looks at options for a electric thruster modules, which can be used singly for smaller missions and in multiple copies for larger missions. There are several types of such thrusters available, but they will be needed in some form if missions beyond Earth orbit are to be done economically. The higher efficiency allows bringing the vehicle back and using it multiple times, a key cost savings. R&D for this phase would be aimed at upgrading the propulsion to higher power levels, and enabling use of mined propellants rather than the scarce Argon and Xenon used today.
Electric propulsion is used within low orbits for drag makeup and orbit change, and then applied in later phases for more distant destinations. Power, thrust, operating life, and radiation resistance will all have to improve for these later uses, so propulsion R&D will be ongoing. An early use for such thrusters is mining the upper atmosphere for fuel, which makes the propulsion self-sustaining. With adequate fuel, mining the Earth's debris belt both cleans up the debris, and serves as a source of raw materials, spare parts, and work repairing and refueling satellites that need it. New satellites delivered and assembled at an assembly platform can also be delivered to their destinations at low cost. One group of satellites to deliver is prospector satellites to observe and return samples from candidate asteroids, to prepare for later mining.
Chemical Propulsion - High thrust engines, such as conventional chemical rockets, are still an attractive option for some purposes, despite lower efficiency. These include landing on bodies with significant gravity wells, and when velocity change or transit needs to be done quickly, such as passing through the Earth's radiation belts. Which propulsion type to use for what part of a trip will need to consider multiple factors including the ability to extract fuel locally. R&D for chemical propulsion will include adapting it to use and store propellants made in orbit, and improving engine operating life.
Phase 0H: R&D for Phase 4B High Orbit Locations
Materials Processing - This is the conversion of raw materials to finished supplies or stock materials. In the early stages this will be NEA materials brought back from Inner Interplanetary orbits to a location near the Moon, such as EML2. This is the least distance to move the full raw materials mass, and provides full time sunlight for power. Early products include shielding, propellants, and water. Extensive R&D is needed to identify the best locations and processes. Alternative locations include:
- Air processing: aboard the scoop ship, or at a low orbit assembly station.
- Asteroid processing: in place at the asteroid, a high orbit near Earth, or lower orbit.
Materials processing is nominally bootstrapped from a set of seed elements, delivered by electric tug to the desired orbit. Until human habitation can be supported, it would rely more on remote control and automation. Some processing operations may not function well, or at all, in zero gravity, and others will benefit or work uniquely in the zero gravity and vacuum conditions. So a major area for research will be for which specific processing flows are to be used under what conditions.
Space Elevators - The Earth's gravity well is too deep for one-piece stationary elevators to span. However, sectional and mobile systems, known as Rotovators or Skyhooks can perform the same task, and use current materials. Each section has a smaller task, and therefore required strength is lower. We also take advantage of orbital mechanics to transit between sections, which requires no materials at all. Various elevator concepts have been theorized, and small-scale experiments flown in space. Significant R&D is needed to bring this technology to a ready state. When traffic volume is not large, and most of it is restricted to low orbits, the savings from a space elevator are not large enough to justify their construction. We therefore place it in this sub-phase, where reaching high orbits gives them greater advantage. Elevator research can be combined with a variable gravity research facility, as both can use rotating structures. An eventual network of elevators can provide fast velocity changes for people and cargo around gravity wells, while electric tugs perform slower transfers between them.
Phase 0I: R&D for Phase 4C Inner Interplanetary Locations
The space between the major planets and moons has traditionally been viewed as devoid of use, to be gotten through as quickly as possible to reach the "real" locations like the Moon or Mars. This view is incorrect and obsolete. Open space has always been known to have a large and constant flux of solar energy, 1360 MW/km2 at the Earth's distance. In recent decades many thousands of asteroids have been discovered in this region, and we continue to find more. There are also new ideas on how to efficiently extract large quantities of materials from the larger bodies. With sources of energy and materials already in place or which can be imported, widespread use of this region should be possible. New technologies and equipment we have identified for this phase include:
Inner Interplanetary Mining - This involves extracting and transporting raw materials from Near Earth Asteroids (NEA), which are the easiest to reach resources after the atmosphere and orbital debris in low orbits. The mass returned by a mining system and tug is on the order of 200 times the equipment mass, which should drastically reduce costs if that mass can be put to use. 82% of discovered NEAs are larger than 30m, and thus more than 18,000 tons in mass. This is too much to move as a unit, so research is needed on the best ways to collect several hundreds of tons of material at a time. Along with the space tugs noted below, the mined material is delivered at first to High Orbit for processing.
Space Tugs - These are needed to move raw materials from where they naturally occur to where they can be processed, and move finished products and other cargo from place to place. Electric propulsion has already been developed, but much larger units are needed for this task, and the tugs should be designed for refueling, so they can be used many times.
Transfer Habitats - We do want to reach the major planets and moons, but do it efficiently and safely. One way to do this is to place habitats permanently in transfer orbits between bodies, such as Earth and Mars. Since the habitats don't move once set up, they can have heavy shielding and greenhouses, and allow travel in safety and comfort. The raw materials come mainly from asteroids already in nearby orbits. Crews use small vehicles to get from the habitats to planetary orbits at each end of the trip. Additional habitats can be set up on the Martian moons as way stations, and eventually other locations. All the locations eventually can produce fuel, do spacecraft construction and repair, and serve as science platforms, so are multi-functional. The research needed is how to build and expand such habitats, and the various systems they need, such as food production/environmental recycling.
Orbital Bootstrapping - Research is need on how best to bootstrap from early energy and materials extraction to large-scale finished locations, with a range of production, habitation, and transport capacity. A future "space city" is not likely to be built all at once in final form, any more than cities on Earth are. The question is then how to build it in smaller increments.
Phases 0J to 0L: [RESERVED]
The following three sub-phases are reserved for further work. R&D topics have not yet been identified for them:
- Phase 0J - R&D for Phase 4D Main Belt & Trojan Locations
- Phase 0K - R&D for Phase 4E Outer Interplanetary Locations
- Phase 0L - R&D for Phase 4F Scattered, Hills, & Oort Locations
Phase 0M: R&D for Phase 5A Lunar Locations
Lunar Mining - Although the Moon is physically close, and obvious to anyone who looks at the sky, it is not the first location to mine. This is due to the extra propellant needed to land on the Moon relative to orbital operations nearby. However, once propellants are produced in orbit, the difficulty decreases and lunar operations can start. The energy to reach Lunar orbit is 1.5 MJ/kg, while typical production energies, from raw materials to finished products, are 10-20MJ/kg on Earth. Since twice as much sunlight is available in high orbits than the Lunar surface, the preference appears to be to send the materials to orbit. More research is needed to see if this is truly the best option, and systems to deliver the materials to orbit efficiently. Candidates include centrifugal and electromagnetic catapults, and space elevators. Lunar surface materials are well mixed from impacts, and low in volatiles from high early temperatures. Their composition is thus different from the major asteroid types, and the best processing flows will also need research.
Phases 0N to 0S: [RESERVED]
The following six sub-phases are reserved for further work. R&D topics have not yet been identified for them:
- Phase 0N - R&D for Phase 5B Mars Locations
- Phase 0O - R&D for Phase 5C Venus & Mercury Locations
- Phase 0P - R&D for Phase 5D Jupiter System Locations
- Phase 0Q - R&D for Phase 5E Outer Gas Giant Locations
- Phase 0R - R&D for Phase 6A Interstellar Space Locations
- Phase 0S - R&D for Phase 6B Exostellar Locations
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Orbital Mining - The reason is the depth of the Earth's gravity well has a fixed energy cost to climb. Obtaining raw materials closer to where you need it would use less transport energy. In particular, obtaining fuel locally has high leverage. Section 4.8 - Orbital Mining looks at alternatives for the mining function. The mass return ratio is an important parameter for mining operations. This is the (materials extracted mass)/(hardware and fuel mass). We look for ratios of 50 or more for atmosphere and asteroid mining, since these are raw materials and further processing is requires. A lower ratio may be acceptable for salvage of equipment and debris in Earth orbit, since they are already manufactured and even operable equipment. These ratios look feasible from the analysis done so far. By using the Moon for gravity assist in both directions, traveling to and from the asteroids can be done with less than escape velocity.
Section 4.9 - Processing Factory looks at the alternatives and options for this task.
A space elevator system in the form of a rotating Skyhook would allow using highly efficient electric thrusters in place of low performance chemical rockets for much of the transport job in gravity wells or between orbits. Section 4.10 - Skyhooks) looks at some alternative concepts for such a system. The first one could be built in Low Earth Orbit, and then others in higher orbits and around other bodies. The Earth's gravity well is too deep to fully span with current materials, so the low orbit Skyhook is not a full ground-to-orbit elevator. Still, reducing the work for a launch vehicle by 30-50% brings dramatic cost reductions. For smaller bodies such as the Moon or Mars, a Skyhook could span the whole gravity well.
As a large transport infrastructure project, similar to a bridge or airport on Earth, the Skyhook is built when traffic demands it and not before, and then expanded incrementally. The materials for the Skyhooks, such as carbon fiber, may come from orbital mining and processing. In that case their construction would not require large amounts of mass to be launched from Earth. Even if all the mass has to be brought from Earth, the potential for improved payload justifies at least more analysis to see if it is feasible.
Section 4.11 - Lunar Development looks at some design options for the Lunar surface. With a Skyhook network in place, including one in Lunar orbit, it would be possible to go to and from the Moon in a robust and low cost fashion. Precursor missions delivered by electric tugs to Lunar orbit, and using conventional rockets to land, could explore and help select a Lunar base location. Remote controlled robots could do some preparation work, like paving landing pads by solar or microwave heating. Expanding on the initial work, heavier mining and processing equipment could be delivered and start to use the relatively large mass and surface area available. Seed factory parts and permanent habitats follow according to a logical progression. The primary question is when to start using the Moon as a location, in the context of other locations and the level of technology.
Section 4.12 - Interplanetary Development looks at concepts to use this space.
Section 4.13 - Mars Development looks at concepts for developing the surface of Mars. Having set up a forward base in the form of a habitat on Phobos, we can next use materials from there to build a Skyhook to reach the Mars surface efficiently, and start to build up facilities on the ground. Precursor missions will have explored and set up seed factories without the benefit of a Skyhook, but major development requires an efficient way to get to and from the surface.
Section 4.14 - Later Projects looks at some ideas for Main belt and later projects. Since technology changes over time, it is not worthwhile to make detailed plans for far into the future. Long range concepts can serve as a guide for future research, though. As the time frame gets closer, ideas like these, or ones developed later can be incorporated into updated program plans.
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