# Space Transport and Engineering Methods/Advanced Manufacturing

The main program goals are upgrading civilization on Earth, and progressively expanding to more difficult environments, including space. To accomplish these goals, some new or improved technologies and methods will be needed. Once available, they can be incorporated into suitable designs for their intended locations. For space locations in particular, there has been a severe lack of production and habitation capacity, with the main focus so far being on transport and information services. 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 as preparation for what's needed for the later phases, and to consciously correct unbalanced development where possible. The major goals of Research and Development (R&D) phase can then be stated as:
* (1) Identify systems and elements covering the full range of production, habitation, transport, and services 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.

## R&D Planning

The program as a whole is complex. Systems Engineering methods (see Section 1.5) have developed to handle such complexity, so we intend to use them to for this and later phases. Other engineering methods will 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 what we would like to do. In those cases, we don't have to change them, just use them. Other items are deficient or undeveloped, and not being pursued elsewhere. 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 will be used internally in the program, and also supplied as a benefit to civilization at large to use elsewhere. These external uses will also be considered in deciding what R&D to pursue.
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 our current knowledge, and on available project resources, mean we cannot do all the R&D work in advance or all at once. In some cases, a given area of R&D must be completed successfully before following work can be done. Since we do not know in advance if we will succeed, we expect that R&D plans will often need to change, or follow multiple paths. We also expect progress across civilization in other technologies, so a given design may no longer be optimal and require upgrades. Therefore the R&D phase is expected to continue in parallel with later phases for as long as the program continues.
Products and services produced as outputs from early phases can be used internally to support later R&D. For example, we may demonstrate self-expansion of an industrial building as an R&D task, and later use that building for further R&D, or as a production area whose product sales finance further work. Field experience from earlier phases can be fed back to the R&D phase to improve later designs. Self-use and feedback should also be considered in R&D planning.

## R&D Process

The R&D process will be 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 - This activity includes coordinating external resource flows, tasking, planning and scheduling, and analyses.
    0.1: Coordinate R&D External Flows - This task includes arranging and managing resource flows into and out of the phase, from outside the program and to other phases.
    0.2: Coordinate R&D Tasking - This activity includes arranging which resources will be applied to the phase tasks.
    0.3: Coordinate R&D Planning & Scheduling - This activity includes developing future plans and schedules for the phase.
    0.4: Coordinate R&D Analyses - This activity examines past performance and studies ways to improve R&D processes.
Task 1: Conceptual Design - This includes exploring new concepts and developing a reference architecture. This is followed by a systems engineering process to reach a concept level design. This includes defining the main functions and elements of the program, and how they will be operated and maintained across the stages of their life cycle. This model is itself part of the conceptual design. Based on prior experience, systems engineering effort optimizes the program cost and schedule at ~10-20% of total effort, with the systems tasks weighted towards the early part of the program. The systems engineering process flow is used iteratively in later design stages. The subtasks here are a template for those flows, but to avoid repetitiveness they are not broken out separately each time below.
    1.1: Explore New Concepts - This step covers taking ideas, such as self-expansion and automation, and applying them to create new products and projects. Some concepts only apply to particular phases or elements, so an application matrix is an output of this task.
    1.2: Develop Reference Architecture - The reference architecture is a high level design used to identify technology risks and readiness level (TRL), and make early estimates of cost and schedule. It is a starting point for the conceptual level design. It includes program goals, an architecture description, high level interfaces, element requirements, and element descriptions. Supporting data for the reference architecture includes data sources, analyses to support concept selection, and tracking from goals to lower elements.
    1.3: Identify Requirements & Measures - These establish measurable features a design must meet, and criteria for selecting among design alternatives. See Section 1.5 Requirements Analysis for details.
    1.4: Perform Functional Analyses - This breaks down what the design does in terms of functions it performs or a sequence of operations. See Section 1.5 Functional Analysis for details.
    1.5: Allocate Requirements - This assigns the requirements from task 1.3 to functions from task 1.4 to ensure they are all met somewhere in the design.
    1.6: Model Alternatives & Systems - There are many possible ways to meet a given set of requirements. Modeling the options provides measurable details for each. The modeling process includes
       (1) Collect External Technical Information: This includes data needed for modeling and later design, such as existing product data, industry specialist contacts, and current state of the art such as books and articles.
       (2) Develop Alternative Options
       (3) Build System Models.
    1.7: Optimize & Trade-Off Alternatives - This includes varying parameters of a design option, and comparing different options, to find the ones that best meet the selection criteria.
    1.8: Synthesize & Document Design - The outputs from this task are articles, reports, and books documenting the chosen concepts.
Task 2: Preliminary Design - Assuming the conceptual design produces a sufficiently promising concept, the next stage is to define the elements of the program in more detail. This is done in parallel with component technology (task 4) and prototype systems (task 5) because otherwise size and performance would be too uncertain. Multiple design alternatives may exist in this stage, until competing technologies and testing is far enough along to permit selection. This follows same steps as conceptual design, but at greater level of detail.
Task 3: Build R&D Locations - This activity includes building or acquiring use of offices, research workshops, conventional production shops, and prototype test areas needed for R&D work. The design requirements for the R&D locations comes from the previous design work, needs for technology development, and for building and testing prototypes. Consideration is also given to adapting the R&D facilities for later phase use.
Task 4: Develop New Technology - This includes identifying the performance needed based on the conceptual and early preliminary design, surveying the status of current technology, ranking areas for improvement in terms of impact, then applying effort in the most promising areas to improve performance or lower uncertainty. Some technologies are already under heavy development outside the program. So rather than duplicate that effort, we select areas where a limited budget can have the most impact, or encourage others to invest in those areas which need the most work. Technology level work is aimed at single processes or components.
Task 5: Build Prototype Elements - At some point it becomes necessary validate integrated elements and demonstrate performance levels by building prototype hardware. This can be simplified versions of what will become final designs, scaled versions for what will be larger designs, or versions that demonstrate the functionality, but do not use the final materials and components because they have not yet been made. Prototype elements may carry over to later phases if they work well enough, or can be upgraded to final versions in some cases.
Task 6: Test Prototypes - This task reduces technical risk by demonstrating the actual performance of prototype system elements. Initial testing would use the local R&D environment conditions, but later testing uses the full range of operating environments, either in test chambers or by taking the equipment to suitable locations. Deficiencies found during testing are fed back to developing new technology. Early prototypes of a given element may have lower performance goals, which are later increased as improved designs are developed. In some cases, test units can go on to be used operationally, and therefore transferred to a later phase.
Task 7: Detailed Element Design - This activity covers detailed design of specific facility locations and equipment. This includes places places where R&D is done, operational facilities for later phases, individual equipment items within these locations, and vehicles and other equipment which moves within and between locations. Detailed designs incorporate existing technology, plus new technology developed, prototyped, and tested within the program. They can also include off-the-shelf equipment, parts, and materials from outside the program when that makes sense. Because of improved technology over time, goals for further expansion and upgrade of existing systems, and development of new locations, this task is expected to continue through the program. Particular designs for complete facilities, processes, equipment, vehicles, and components can be used in multiple projects and phases, or sold as separate products.

## R&D Sub-Phases and Tasks

The sub-phases, and the R&D tasks identified for them so far, are listed below. This list is preliminary, since concept exploration for the later program phases is incomplete. The tasks are listed in the order we identified them, rather than time order, since determining the best sequence for the work and schedule planning is a later step. For identification we use the plain "Phase 0" label, with no additional letters, to identify general R&D work 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 the R&D work applies to two or more later program phases it is identified with all applicable sub-phase letters, thus 0CD or 0G-L. Since some R&D locations may themselves need new technology and design, the first lettered sub-phase, 0A, applies to Phase 0 itself.

### Phase 0 - Program-Wide R&D

The program's goals are to establish new locations for civilization, and upgrade existing ones. We have identified self-expanding systems, using Seed Factories as starting points, as a key technology to reach those goals. It can be applied to existing locations across current civilization, and to new ones both on Earth and in space. The general approach of self-expansion includes more specific methods like distributed production networks, remote-controlled operation, and smart tools which can operate themselves. Manufacturing in general, and automation in particular, already get a lot of engineering effort, so we do not need to duplicate those efforts. Our R&D work will focus on the unique aspects of self-expanding systems, and integrating other technologies into them.
Self-expanding systems, seed factories, and the related ideas fit within the more general subject of Advanced Manufacturing. They can be used anywhere, including both developed and undeveloped regions on Earth. However, the main subject of this book is space systems. So we devote a separate book entitled Seed Factories to general discussion of those ideas, and their applications on Earth. We provide a short introduction here, and mention such systems where they are used in later phases.
Seed Factories Introduction - All factories produce products, and some factories produce the same kinds of products they use themselves. For example, a Steel Mill typically uses some steel in its own construction. Self-expanding factories are specifically designed to use their own output to grow. A "seed factory" is an optimized starter set of people and equipment. It includes plans and instructions for a chain of expansions to reach some desired mature state. It may also include a starting inventory of materials and parts to use in production. Using tools to make more tools is not a new idea. In fact it is nearly as old as tool-making itself. What is new is optimizing for a small starter set to bootstrap the process, applying modern computer systems, automation, robotics, and AI to the task, and combining several growth paths to increase output:
* Making identical copies of the starter equipment,
* Making larger versions of, or extensions for, the starter elements, and
* Making new tools and machines not in the original starter set. These can be used for new tasks, and expand the range of possible outputs.
The present state of technology does not allow for full artificial Self-Replication, which means copying 100% of its own parts and doing so without help from people. Self-expanding systems therefore include more than just the factories that make physical products. Whatever parts and materials a factory cannot make itself have to be supplied from elsewhere, therefore transportation is needed. The people required to run the factories have other needs and desires beyond their work. They also need places to live, food, and a variety of services. In developed areas much of that is already available. But in undeveloped parts of the Earth, and in space, complete self-expanding systems will need production, transport, habitation, and services in order to grow. Unlike current machines, people and other biological systems can copy themselves. So they can grow as needed within a complete self-expanding system.
The seed factory approach should be worth developing on Earth for its own sake. It should make setting up new factories cheaper, especially in remote or difficult locations, because you only need a starter set and not the full factory. With an emphasis on self-growth, they may also achieve high economic rates of return. Once developed on Earth, industrial-scale factories can produce items needed to reach space, such as launch sites and rocket factories. New starter sets can then be 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 much more affordable.

### Phase 0A - R&D for Phase 0 R&D Locations

Even when no new equipment designs or technology is needed, research and development for later phases will need offices, laboratories, prototype fabrication, and test sites. 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 other equipment for the later phases. Specific needs for this phase have not yet been identified.

### Phase 0B: R&D for Phase 1 Starter Projects & Network

Starter Sets & Bootstrapping Paths - Work is needed to identify the best starter sets and growth paths for small-scale production, and what new technology and designs, if any, are needed. Some people already have sets of tools they can use immediately. Many other off-the-shelf tools and machines are available at reasonable cost. These may be sufficient to start the bootstrapping process, but some custom designs may be helpful. Plans and instructions that people can follow need to be recorded and distributed, along with whatever training materials are needed for people who don't have the necessary skills and experience.
Distributed Production Networks - Traditional factories and large office buildings brought 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 need to be in one physical place, and allow coordination of distributed work in many places. Some prominent examples are development of open-source software, and Wikipedia. In a modern production system, the control of the machinery can be a mix of a on-site people, remote control by people, 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. Remote operators can efficiently split and re-assign their work as needed between locations.
It is likely that some machines and workers will still be grouped together in shared locations, for efficiency or other reasons. Modern technology merely removes the requirement that they all have to be om one place. Distributed production is helpful in the earliest stage of small-scale operation, because you can avoid the cost of a dedicated larger site. Instead, people can use spare space where they already live, or temporary work sites when and where needed. Multiple small efforts like these can then combine to finish larger projects. We therefore place initial R&D for distributed production in Phase 1, but can use it in all the later phases.
Some of the needed technology for distributed production already exists. The R&D tasks for this sub-phase are then to improve or fill in the parts that do not, and combine them into flexible distributed networks. The flexibility is needed because the program intends to constantly add new locations, and existing ones will self-expand. So we cannot operate on the basis of static networks. They have to grow and adapt along with the rest of the program.
Applications to Later Phases - In this phase, a goal for distributed production technology is the capability to connect and operate hobby and home improvement level equipment in fairly close proximity, like a single metropolitan area. Later phases would need upgrades for long-distance remote operations, such as on the Moon from Earth, or Mars from Phobos. More R&D may be needed later on in this technical area. 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, and using smart tools which can operate themselves. So at first there will be a strong incentive for the upgraded technology. As factories, habitats, and transportation systems are built for the later phases, people can be supported more easily on-site. So the optimum balance of local people vs remote and smart tools will shift. Having gained experience with the distributed approach on Earth, using it in space will not be something entirely new, but rather an extension of what was learned in earlier phases.

### Phase 0C - R&D for Phase 2A Distributed Locations

R&D for this sub-phase involves design of more specialized and larger machines than for 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 uses the largest size equipment.

### Phase 0D - R&D for Phase 2B Industrial Locations

This sub-phase completes the sequence of growth to larger and more specialized equipment, for developed locations in moderate environments on Earth. It includes equipment for the full range of production, habitation, transport, and service industries. Equipment for all these industries already exists, and is widely produced. The R&D for this sub-phase includes modifying their design so they can be made by self-expanding and distributed systems. It also includes the growth paths and methods to reach industrial scale from the smaller scales in earlier phases.
More specific R&D tasks may be identified later, for particular industry groups or individual industries. One that we know of at this point is industrial transport to Low Orbit, since it will be needed for the later program phases in space:
    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 transport from Earth to orbit, and back. 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 transport needs.
In the earlier parts of phases 4-6, transport needs to orbit will be relatively small. They can use existing launch systems, or ones currently in development, to avoid the cost of unique development. 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 4.4, 4.6, and 4.7 present some early concepts for this R&D work. In section 4.4 - Phase 2B Industrial Locations 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 4.6 - 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 4.7 - 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 area available outside the program. Some candidates to 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 or 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 small 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 Development

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 fully 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
1.2. Supply Power - Electrical power using solar panels and batteries is fairly well developed for low orbit. Sunlight is available at least 60% of the time, but only special low orbits have it all the time. So energy storage is needed to bridge the time in the Earth's shadow. Thermal power using solar concentrators is an area for R&D.
1.3. Extract Materials - Low orbit has two significant sources of materials besides those brought from Earth or more distant locations. The first is the upper fringes of the atmosphere, which can be collected by an orbital compression scoop. The second is space debris, which includes non-functional satellites, empty stages, and collision fragments. Some of the gathered gases can be used as propellant for collecting the 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 4.5 - 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 its 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
Partial Gravity Research - There have been a series of space stations in low orbit, which provide experience in zero gravity conditions. For people, at least, long periods of zero gravity (up to a year) are detrimental to health. We have essentially no information on what gravity levels between 0 and 1g do to people and other living things. Therefore we don't know what designs are needed for long-term habitation or agriculture. Besides living things, some production methods work better with gravity, but the minimum required isn't well understood. A Variable Gravity Research Facility would start to answer these questions by providing adjustable artificial gravity. The design can include one or more modules on a rotating arm, and their position and rotation rate adjusted to get desired gravity levels. An alternate course is to assume full Earth gravity as a design requirement at first, then pursue partial gravity research on an "as available" basis. For example, a rotating habitat which produces full gravity at the rim will have areas of lower gravity that can be used for research. Research stations on the Moon and Mars can provide data on their particular gravity levels, limiting stay times for people to less than a year at first, until more experience is gained.
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-g to some gravity 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 R&D 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 4.8 - Electric Propulsion looks at options for propulsion modules, which can be used singly for smaller missions and in multiple units for larger missions. There are several types of electric engines 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 Xenon used today.
Electric propulsion can be used within low orbits for drag makeup, for changing orbits within the region, and to reach more distant destinations. Power, thrust, operating life, and radiation resistance will all have to improve for these later uses, so propulsion R&D would be ongoing. An early use for such engines is mining the upper atmosphere for gases, as noted at item 1.3 Extract Materials above. Some of the gases can be used for propellant, which makes the propulsion self-sustaining. With sufficient propellant, mining of orbital debris becomes feasible. New payloads delivered to Low Orbit can also be delivered to their final destinations efficiently. One early category of missions are prospector satellites to observe and return samples from Near Earth 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 produce propellants locally. R&D for chemical propulsion will include adapting systems to use and store propellants made in orbit, and improving engine operating life.
Spaceport Network - In the long run, large numbers of vehicles changing their orbits by consuming propellant is inefficient and wasteful. Large scale infrastructure which reduces propellant needs would be desirable. We will refer to them as Spaceports by analogy to maritime and airports. Their main function is transport of payloads by potential and kinetic energy change. They would also serve as transportation depots, with docking for multiple vehicles, habitation, warehousing, maintenance, fueling, etc. The first concept for such infrastructure was the Space Elevator, which dates back to 1895. Unfortunately the Earth's gravity well is too deep for the original idea of a one-piece stationary elevator to work with any known materials. The original idea can work for smaller bodies, and systems with several smaller pieces can do most of the velocity change for Earth using available materials. A network of spaceports can eventually replace much of the propellant used in space, and increase the percentage of payload transported. The R&D work for such a network is placed here because the first spaceport would likely be located in low orbit. Section 4.11 - Space Elevator looks at some alternative concepts for such a network.
The basic transport function is accomplished by Momentum exchange between a payload and the spaceport structure. Depending on direction, the payload gains or loses energy, and the opposite happens to the spaceport. If traffic is balanced, or the spaceport is anchored to a more massive body, its orbit is not affected. Unbalanced orbit changes are corrected by an efficient propulsion method on the spaceport. To the extent this replaces lower efficiency vehicle propulsion, especially when reaching orbit from the Earth's surface, there is a net savings. Various experiments have been done in orbit related to this technology, but much more work is needed. Improvements in other technologies beyond momentum exchange are needed for a complete spaceport network and associated vehicles.

### Phase 0H: R&D for Phase 4B High Orbit Development

High Earth Orbits are currently used by a number of remote-controlled satellite types, including communications, scientific, and navigation. They are all delivered from Earth, and local production and habitation don't yet exist. Transport is only that built-in to the satellites when delivered. The High Orbit region is fairly devoid of native materials, but has a high level of solar energy, and is accessible from Earth, the Moon, and Near Earth Asteroids. Between current civilization on Earth, and future locations beyond it, it can serve as a useful production and transport nexus, and later for large-scale habitation. Fully developing this region will require extensive R&D work. Some identified tasks include:
    1. High Orbit Production
1.4 Materials Processing - This is the conversion of raw materials to finished supplies or stock materials. In the early stages this can be asteroid materials brought back from Inner Interplanetary orbits to a location near the Moon, such as Earth-Moon Lagrange Point 2 (EML2). EML2 is a Lunar-synchronous location 64,500 km behind the Moon's center. It is low energy to reach from interplanetary orbits, 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. As additional regions in space are developed, raw materials can be supplied from the Moon and farther asteroids, and possibly Low Orbit. Materials coming from Earth will generally be in finished condition, since processing on Earth is less expensive. They would include items like alloying elements for metals, and doping elements for electronics. How finished materials coming from other space regions will be depends on the balance of local processing energy vs transport energy, and what fraction of the ore can be used.
Earlier phases of the program should have developed experience with self-expanding production and remote operations. We assume materials processing begins with finished equipment brought from Earth, then bootstraps further expansion by adding seed factory elements, which use the early supply of processed materials as inputs. Until larger human habitation can be supported locally, it would rely mostly on remote control and automation. Some processing operations may not function well, or at all, in zero gravity, and others will benefit from or work uniquely in the zero gravity and vacuum conditions. So a major research area will be which specific processing flows are to be used under what conditions.
1.7 Assemble Elements
Large Space Structures - Large orbiting structures like the Space Station have been assembled using alignment guides and motorized bolts. For future projects needing large pressure-tight compartments, one option is welding, which is a basic industrial process on Earth. Welding of metals has been achieved by concentrated solar energy (Romero, 2013). Since high-quality solar energy is widely available in orbit, research on using it for welding in space seems worthwhile. For assembling large structures like habitats, where moving the structure would be difficult, one method is to use articulated mirrors to direct a beam of concentrated sunlight at various angles. Another approach to large structures is laying high-strength reinforcing fibers between layers of plasma-sprayed metal. Spools of fiber and metal wire are compact and modular, but the finished structure can be large and seamless.

### Phase 0I: R&D for Phase 4C Inner Interplanetary Development

Section 4.7 - Inner Interplanetary Development describes our concept exploration for Phase 4C of the program. So far we have identified one general and several specific R&D subjects to work on for this phase:
Interplanetary Bootstrapping - Self expanding systems are a general approach used throughout the program. This R&D topic is about how best to grow from early materials extraction from the region, to large-scale finished locations, with a range of production, habitation, transport, and services 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 start small and build them in increments.
    1. Inner Interplanetary Production
1.3 Extracting Materials
Mining on Earth is very well developed, but extracting materials beyond our planet is still in the early stages of remote sensing and robotic prospecting. Therefore extensive R&D is still needed for this production step.
The general rationale for mining in space, rather than bringing everything from Earth, is based on minimizing total energy use. The Earth's gravity well has a fixed energy cost of 31–62 MJ/kg to climb, depending on orbit. Existing transport methods are inefficient, multiplying the minimum value by approximately 9:1. Destinations beyond Earth orbit require even more energy to reach. The production energy from raw materials to finished products is typically much less than this, in the range of 10–20 MJ/kg. Industrial equipment can normally process many times its own mass, and use many times the energy required to make it during its operating life. So the product/equipment ratio is high. It therefore takes far less total energy to deliver starter production equipment, and make the rest of the equipment and finished products from local materials and energy, than to deliver the all finished products from Earth. Local production includes making propellants for space transport, which makes the delivery of starter equipment to distant locations easier.
Early Mining - Section 4.9 - Orbital Mining looks at alternatives for supplying raw materials to the Low and High Orbit regions. These would at first come from the Near Earth Asteroid (NEA) group in the Inner Interplanetary region, and be delivered to a processing location near Earth. NEAs are the next easiest to reach materials after the atmosphere and artificial debris in low orbits, and development is likely to proceed outwards from Earth. Remote control of operations from Earth and supplying live crew makes processing closer to Earth is easier at first. High orbits are a convenient meeting point for asteroid, lunar, and Earth source materials, and they also get full-time sunlight. Most of the uses for early products will be in Earth orbits too. So that seems to be the preferred starting point for production.
The mass returned by a mining system and tug from a nearby asteroid to high orbit is on the order of 100 times the equipment mass per trip. The tug's service life is on the order of 6 trips taking 2.5 years each before major component replacement is needed. A typical trip consumes 2.6% of the returned mass in propellant, but certain asteroid types contain up to 20% easily extracted propellant. This propellant consumption assumes the Moon is used for gravity assists in both directions, making the propulsive velocity change less than that to reach Earth escape. So the mining operation can be self-fueling after the first trip. Counting hardware plus initial propellant load, the tug will return about 160 times the starting mass during its life. Mining should drastically reduce operating costs in space, if that mass can efficiently be put to use. Other production equipment will be needed beyond the tugs which bring back the raw materials, but at least the first step has a large positive return.
NEA orbits and compositions are randomly distributed. We prefer to mine the easiest to reach ones at first, when they are in optimal positions and at the best times. Given over 17,000 objects discovered in this group so far, there will be some in such easy to reach orbits. But which ones are best to visit varies with time, because they are in constant motion. 81% of discovered NEAs are estimated to be larger than 30 meters in diameter. They have a mass of at least 18,000 tons and usually much higher. This is too much to move as a unit for early tugs, so R&D is needed on the best ways to collect smaller loads of material from them.
Long Term Mining - As development extends outwards from the Earth Orbit regions, the destination for raw materials will shift to Inner Interplanetary locations, and the source materials will come from the entire region, rather than just the ones easiest to reach from Earth. Depending on the technical details of extraction, processing, later production steps, and final use locations, materials may continue to be transported in the raw state, or production plants brought to the source materials, and more finished products delivered elsewhere or used locally. The size of the asteroid is likely to be a strong factor in this choice. For example, 433 Eros, a large asteroid in this region, has a mass of 6.69 trillion tons. So it is more likely to be worth setting up local production ton Eros than one of the smaller asteroids which only mass a few kilotons. As more distant orbital regions, and Mercury, Venus, and Mars become developed in later phases, they can also become sources of raw materials to bring to the Inner Interplanetary region.
1.4 - 1.8 Materials Processing & other Production Steps
Materials processing methods, like ore reduction and chemical technology, are also very well developed on Earth. They have seen essentially no use in space beyond some experiments in orbit and prototypes on Earth. So extensive R&D is needed for this and the later production steps. A few uses, like bulk radiation shielding, don't require changing materials from their raw state. But nearly all other materials need some processing to turn raw materials into finished materials inventory. Some materials, like propellants, water, and oxygen, can be used as-is once extracted. Other materials, such as metals and ceramics, need further fabrication into parts, then assembly to make finished products.
Section 4.n - Processing Factory looks at concepts for the processing part of production. We expect previous designs to have been developed for the Low and High Orbit regions. Additional R&D needed for this phase involves adapting and optimizing the processes for the unique conditions and source material in the region, and brought to it later from other regions. An example future changes is production closer to the Sun, where making use of increased solar flux is desirable. Fabrication and assembly methods may not need changes from previous orbital regions, but this is still to be determined.
    3. Inner Interplanetary Transport
3.1 Bulk Cargo Transport - Electric "Space Tugs" 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. Tugs generally do not need human crews, and are slow but efficient. Electric propulsion has already been developed at smaller scales, but much larger units are needed for this task, and the tugs should be designed for refueling, so they can be used multiple times. We expect smaller tugs to have been developed for the Earth orbit and Lunar regions. So for this region, the main R&D work is on building larger and longer-lived versions.
3.3 Transport People - We want to eventually carry people to open space locations and the major planets and moons in the Inner Interplanetary region. However, radiation is present throughout the area from the Sun and cosmic sources. "Transfer Habitats" are a way to carry people safely and efficiently. These are placed in repeating transfer orbits between bodies or locations, such as between Earth and Mars. Since the habitats don't change orbit once set up, they can have heavy shielding, greenhouses, and processing equipment. The raw materials come mainly from asteroids already in nearby orbits. Local production reduces payload needed from Earth, and gives the crew and passengers something useful to do during the trip. Small vehicles are used to get from the habitats to planetary orbits at each end of the trip. One way to save on high thrust propellant is to use momentum exchange for the small vehicles, making up any needed velocity change on the habitat with electric propulsion. The habitats can grow over time, eventually becoming destinations themselves.
Additional habitats can be set up on the Martian moons as way stations, and eventually other locations. All the locations would eventually become multi-function, combining transport and other purposes. This is possible in space, because unlike Earth, everything is in relative motion. We can make use of that motion for transport while doing other things. This would include producing propellants and other supplies, spacecraft construction and repair, serving as science platforms, and as the nucleus for later permanent colonies. Extensive R&D is needed on how to build and expand such mobile habitats, and the various systems they need, such as food production and environmental recycling.

### Phases 0J to 0L: [RESERVED]

The following three sub-phases do not yet have identified R&D tasks. Their sub-phase headings are reserved for later use.
* Phase 0J - R&D for Phase 4D Main Belt & Trojan Development
* Phase 0K - R&D for Phase 4E Outer Interplanetary Development
* Phase 0L - R&D for Phase 4F Scattered, Hills, & Oort Development

### Phase 0M: R&D for Phase 5A Lunar Development

Development Sequence – The Moon is physically near the Earth, and visible to anyone who looks at the sky. Despite the obvious destination, the Lunar surface is not the first place we want to start development. This is because the Low and High Orbit regions around the Earth and orbits around the Moon are all easier to reach than the surface. Developing orbital vehicles and supply depots first makes reaching the surface easier, so we start those phases earlier, but then continue them in parallel. Scientific observation of the Moon began as soon as telescopes were available, and local exploration began once rocketry enabled getting close to it. Since 1958, over 100 Missions have been attempted to flyby, impact, orbit, land, drive on, return samples from, or use the Moon for gravity assist. Many of these have succeeded, including six landings with people. We expect such science and exploration activity to continue, and provide the basic knowledge needed for useful development. The Lunar region includes two distinct environments. These are the surface and body of the Moon itself, and orbits averaging 35,000 km or less from the Moon's center, where the Moon's gravity is dominant. Each environment requires distinct designs to cope with and make use of the local conditions. Since the Moon orbits our planet, the entire Lunar region is embedded in the larger High Orbit region around the Earth, and moves within it.
Many of the technologies and systems needed for Lunar development are not ready to use today. So significant R&D work will be needed prior to designing and building future Lunar projects. We assign the necessary Lunar R&D work to this phase. Some of that work may be carried out on Earth. Other parts may require using the Low or High Orbit regions, or be directly performed in Lunar orbit or on the surface. The ones which cannot be performed on Earth will require suitable transport and supporting systems such as communications. This in turn may require R&D and projects from earlier phases first be completed. The outputs from the Lunar R&D are then supplied to Phase 5A for their use. An important question is when to start using the Moon in the context of developing other regions, and the level of available technology to do so.
Section 4.12 - Lunar Development begins the concept exploration process for developing the region. That process includes identifying what R&D is needed for the various locations and projects in the region. We organize and discuss those needs in this section according to major function (production, habitation, transport, and services) and lunar environment (orbit and surface). The list is almost certain to be incomplete and need updates over time. We cannot predict in advance which technologies will work, or prove better than their alternatives. So this information will feed more detailed R&D and program planning on a continuing basis.

#### 1.0 Lunar Production

Bootstrapping Methods – The question of how best to build up industry in the Lunar region as been studied to some degree. For example, Metzger et. al. have modeled bootstrapping industry on the Moon, and found 12 tons might be sufficient for a starter set. Under a fairly wide range of assumptions, that starter set could grow to a much larger installation. However, much more study is needed to account for multiple sources of materials, orbital vs surface activities, production methods, and the build-up of infrastructure over time. There is enormous production experience on Earth. However self-bootstrapping from starter sets is still mostly theory on Earth, and production of any kind has never been tried in the Lunar region. Sustained R&D is needed on this subject, both on Earth and for the Lunar region.
    1.1 Lunar Orbit Production
Production Locations – The energy from the Lunar surface to orbit is 1.5 MJ/kg. Typical production energies, from raw materials to finished products, are 10–20 MJ/kg on Earth. Production energies are likely to be similar in space. Gathering raw materials from the Lunar surface is fairly low energy, since repeated impacts have pulverized the surface into a Regolith of loose rocks and dust. Twice as much sunlight is available in high orbits than the Lunar surface. So the preference appears to be to send materials to orbit for further processing, since it can be completed faster.
High orbit can also be a meeting point for materials from the Moon, asteroids, and Earth. Lunar surface materials are lower density minerals, well mixed from impacts, and low in volatile compounds. This is due to the Moon's high early temperatures and low escape velocity. Asteroids usually did not get heated as much, and their denser components have been exposed by collisions. The Moon's denser materials are trapped deep inside. So available materials from the Moon are different from those found in the major asteroid types. Some materials are rare or absent on both the Moon and asteroids, and are more easily brought from Earth. Using all three sources allows a wider range of processes and products than from the Moon alone. The Moon is likely to be the main material source by mass because of low distance and energy.
    1.2 Lunar Surface Production
The preference seems to be for most production to be in orbit. However local production for use locally on the surface will likely make sense, and in some cases so will surface production for delivery elsewhere. Like for orbit, extensive R&D is needed to determine what products and processes will be the most useful, and how to bootstrap from starter sets of equipment. Some candidates include:
Sintered Regolith – Sintering forms a solid mass from particles by applying heat or pressure, but not complete melting. Example products are paved landing and building pads , roads, and blocks for structures and shielding. Rocks and dust are widely available on the surface, as is sunlight which can be concentrated. Vacuum conditions make binding the particles easier and reduces losses from heating. It is also a simple process, which can be done robotically. These features make it a good candidate for early production. An alternative or supplement to solar heating are microwaves, which heat from the inside rather than outside.
Direct Extraction of Native Iron – Iron-bearing meteorites have impacted the Lunar surface since Since its origin. From Apollo mission rock samples we know around 0.5% of the surface regolith layer is bits of native iron (Morris, 1980). It is generally as small particles formed by exposure reduction, micrometeorite impact, or from the source bedrock. The regolith also has 5–13% iron in the form of mineral oxides, but native iron does not have to be chemically processed, which avoids complexity in early production. Potentially you can extract the native iron fraction with a magnet, then separate it from impurities with a furnace, and sand-cast the result into molds made from the abundant fine particles on the surface. Research is needed into the feasibility of the process, and whether early production of iron is worthwhile relative to more complex chemical reduction. The latter can produce up to 25-30% of the ore mass in the structural metals Al, Fe, Mg, and Ti; 20% Silicon for power, and 40% oxygen for life support. Chemical production can therefore make much better use of a given amount of mined material.
Ceramics and Metals Production – Ceramics, such as bricks and crucibles, and metals of all types, are key elements in any modern production. Extensive R&D is needed in how to extract the desired materials, and convert them to useful products on the Lunar surface and in orbit. Thermal processes are common in both categories, so making solar concentrators and furnaces is an important area of study.

#### 2.0 Lunar Habitation

Low-gravity Effects – This R&D task is to determine the minimum safe levels for people and other living things over extended times. Extensive research has been done on zero gravity, but not on levels between zero and one gee. Low gravity, and even extended bed rest on Earth, are known to have adverse consequences for people. We also do not know the long-term effects of low gravity on plants and animals. Artificial gravity can be supplied by rotation, both in orbit and with surface centrifuges. There may be subtle side effects from artificial over natural gravity. All of this needs to be resolved before long-term Lunar habitats are designed. We expect much of this work will have been done in the earlier Earth Orbit phases, because the same problem occurs there. The natural Lunar surface gravity provides an opportunity for research, while early occupation is limited in stay times.
    2.1 Lunar Orbit Habitation
Halo Orbit Station-Keeping – Halo orbits are potential production locations, since they are accessible to both asteroid and Lunar material sources and in sunlight nearly 100% of the time. However, they are unstable, so station-keeping is needed to stay in position. Required accelerations are about 120 m/s/year, or 3.8 × 10$^{-6}$ m/s$^2$. Solar light pressure from a good reflector amounts to 0.08175 N for a 100×100 m area. This provides the desired acceleration to a 21.5-ton mass. Metallized 7.5-micron Kapton Film has a mass of 106.5 kg for this 100×100 m area, or 0.5% of allowed mass. Electric propulsion would consume ~0.25%/year in propellant mass. Kapton films in space have demonstrated long service lives, so they are an example of a potentially a lower mass solution. Since solar panels and furnace reflectors will have significant collection areas, a combination of light pressure on them and placement near the Lagrange point may be sufficient to maintain position. Otherwise additional reflector area can be supplied to control drift. R&D is needed to determine the best station-keeping strategy and design of reflectors when needed.
    2.2 Lunar Surface Habitation
Lunar Dust Mitigation – Lunar surface dust is fine and abrasive, and may present other hazards to people and equipment. It can be disturbed by equipment operations, and possibly natural electrostatic effects. Research is needed to determine the best ways to reduce or eliminate dust problems.

#### 3.0 Lunar Transport

This section covers transport systems based in Lunar orbit or on the surface. Systems needed to reach the Lunar region, but based on Earth or Earth orbit are covered under their respective phases. Current transport methods for the Lunar region include chemical rockets and several kinds of electric propulsion. New development is needed for specific lunar systems using these methods, and additional research for newer methods.
    3.1 Lunar Orbit Transport
Different types of transport systems are preferred for early, low volume traffic, and for later, high volume traffic, where lower cost becomes more important. The requirements for carrying people are different than for cargo, as are the requirements for orbit-to-orbit and orbit-to-surface transport.
Reusable Landers – Landers are capable of reaching the Lunar surface unassisted, and are suited to early development. The first successful landings were in 1966, have continued since then, and more are expected in the future. However, all such landers to date have been single-use. Future improvements would be to develop a reusable lander, which can refuel in orbit, on the surface, or both.
Orbital Cargo Tugs – Electric tugs are efficient but slow methods to move cargo. They would previously be developed for Earth orbits, but units would can later be based at and refueled in Lunar orbit. Gravitational forces are small in the High and Lunar Orbit regions, so transport between them and to more distant regions is relatively easy.
Lunar Orbit Spaceport – A spaceport is transport infrastructure which makes travel easier, but does not itself travel, much like airports function for airplanes. Such infrastructure makes sense when the frequency and volume of traffic is high. The construction cost can then be distributed over many uses. One transport function is propellant supply. Vehicles then only need to carry propellant for one trip, but can refuel as needed for multiple uses. Another is momentum transfer via structural elements. If traffic is balanced in direction and mass, this requires no net energy. It is faster than electric, but still can use that method to save propellant mass by storing orbital energy in the spaceport's mass. The spaceport can support additional functions beyond the basic transport ones. One example is monitoring and control of uncrewed systems in the Lunar region. The reduced distance relative to Earth enables closer to real-time operation. Another is providing radiation protection and artificial gravity for people. The spaceport would start small and grow over time, as traffic and other functions require. It would also exist as part of a larger spaceport network which enables robust and low-cost travel across the Solar System.
    3.2 Lunar Surface Transport
Surface Rovers – Surface vehicles are well developed on Earth, and a number have been operated on the Moon and Mars. However, improvements are needed in load capacity, durability, dust mitigation, and traction. Existing lightweight rover designs are suitable for exploration and site selection. They are probably inadequate for heavier tasks like site preparation and mining. We have no experience yet with maintenance for heavily used machines on the Moon, especially for remote-controlled ones. We also have not unloaded or assembled large vehicles there. These subjects need some research.
Bulk Cargo To Orbit – If much of the processing is to be done in high orbit, an efficient way is needed to deliver bulk raw materials from the surface. Candidates include centrifugal and electromagnetic catapults, and large orbital infrastructure, all of which require significant R&D. The current baseline is chemical rockets, but they have fairly low mass return ratios and are not very energy efficient.

#### 4.0 Lunar Services

    4.1 Lunar Orbit Services
[TBD]
    4.2 Lunar Surface Services
[TBD]

### Phase 0N: R&D for Phase 5B Mars Locations

Section 4.14 – Mars Development explores concepts for developing Mars and the orbital region around it. One approach is to start with a habitat on Phobos. At first can we use local materials from that Moon to support trips to the surface. Since we don't yet know the composition of Phobos, other materials may be needed from nearby asteroids. Since Mars skirts the inner edge of the Asteroid Belt, there are many candidates to choose from. At first we produce propellants and crew supplies. Later we can construct spaceport structures to exchange momentum and reach the Martian surface more efficiently.
We already have a number of satellites in orbit about Mars, and landers and rovers exploring the surface. With a propellant supply in orbit, we can start to land more substantial equipment and build up larger facilities on the ground. These can be remote-controlled from orbit until enough habitat capacity is available for full-time crew. Early missions can deliver seed factory components to start local production. With surface propellant production, and later large ground accelerators coupled to orbital spaceports, access to Mars will be much easier in both directions, and large-scale development can proceed.
All of these concepts are preliminary at present, and will likely need extensive R&D before definite project plans can be made, and actually implemented.

### Phases 0N to 0S: [RESERVED]

Section 4.N - Later Projects looks at some ideas for later phases. Since technology changes over time, it is not worthwhile to make too many detailed plans 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 new ones developed in the future, can be incorporated into updated program plans. The following five sub-phases do not yet have specific R&D tasks identified yet. Their section headings are reserved for later use:
* Phase 0O - R&D for Phase 5C Venus & Mercury Development
* Phase 0P - R&D for Phase 5D Jupiter System Development
* Phase 0Q - R&D for Phase 5E Outer Gas Giant Development
* Phase 0R - R&D for Phase 6A Interstellar Space Development
* Phase 0S - R&D for Phase 6B Exostellar Development