Section 4.1: Program Overview< Space Transport and Engineering Methods
This section summarizes the program as it has been developed so far, which far from complete. Designs presented later in Part 4 are candidates from which a complete program could be assembled. More work needs to be done on them individually, and to assemble them into a coherent program.
The program is aimed at expanding human civilization beyond its current environment range for a number of reasons listed at the start of Part 4. The program as a whole applies a dual path to meeting these desired goals. The first is enabling the expansion by developing improved technology in areas like self-production, recycling, and automation. The second is implementing the expansion to increasingly difficult environment locations. We apply a generalized development model at each new location, adding new functional elements that allow internal growth and later expansion to the next location in a repeating cycle. The expansion cycle begins with seed production elements on Earth. The seed elements build up a production capacity by making expansion equipment for themselves. When sufficiently built up, they start to produce habitation, transport, and more seed elements for the next locations. As more seed elements get added and improved, and as expansion equipment gets made, locations can produce more for themselves and upgrade quality of life and other features step by step. Along with the growing locations, technology development continues so that higher levels of performance can be reached.
When a sufficient level of production and technology is reached, the Earth locations start to produce transportation vehicles and space hardware to establish new locations in Earth Orbit. Orbital mining, added seed equipment, and construction of habitats follows, and finally assembly of transport vehicles to establish the next space location, in High Earth Orbit. The cycle repeats, gradually expanding the number of locations, while existing locations are expanded in size and quality. As traffic grows, early transport systems get replaced by more advanced ones when it makes sense. Once established, individual locations are intended to be permanent, with new ones added in an expanding network.
The sequence of growth is intended to be self-funding, since the benefits of self-expanding production and other new technologies should be enough to pay for the later steps. Thus technology development should come before the first locations are built. The program as a whole is currently at a preliminary concept level so the program elements listed below are likely to change.
A complex program will have a structure with multiple levels. At the highest level we have the program as a whole. Lower levels break the program into successively smaller elements, to the point that single elements can be individually designed and implemented. For this program, we first break it down into phases by time. Each phase aims for better results based on our evaluation score. The next level is a set of locations with increasingly difficult environments. These locations are occupied in series to expand civilization and meet the program goals. The fourth level is the set of functions which each location provides.
Level 1: ProgramEdit
At the highest level is the choice among continuing with what is already in progress and planned, which we call the Existing Baseline, implementing a New Program with new elements, or a partial mix of existing and new. We are not able to recommend which choice to take until the Conceptual Design is much more complete. At some point it hopefully will become clear which choice is best.
Level 2: PhasesEdit
The program phases are defined for now by aiming for a 10 point increase in evaluation score per phase. Early estimates of the existing baseline indicate a score of 20 points, so Phase I would aim for a score of 30, Phase II for 40 points, and Phase III for 50 points. Once the design alternatives are better understood, and what performance is feasible, the number and spacing of phases may be changed later.
Technology Development (Phase 0)Edit
This included the precursor work before full implementation of the program. It includes conceptual and preliminary design, technology development, and prototype systems. Once sufficient progress is made and uncertainties reduced, the program can advance to the full development phases.
Phase I aims at a 10 point improvement over the existing baseline. The baseline is estimated to score 20 points, thus this phase aims at 30 points. The exact program parameters to reach this score depend on many lower level choices still to be made, and technology still to be proven. We know that this phase will involve some number of Earth and Near Space locations, and some level of improved technology.
Phase II would aim at a further 10 point increase in program score. This will likely require more technology development, and because of the time span since the preliminary phase, some redesign and upgrade of Phase I elements will likely be needed.
Phase III is currently aimed at a program score of 50 points. Because it is further out in time and difficulty, this phase is left as a more preliminary concept, more to guide the direction of the earlier phases. Unanticipated new technology is likely to affect designs this far in the future. Phases after this one (IV+) are therefore reserved for future design work.
Level 3: LocationsEdit
Locations are defined by a set of environment, time, and distance parameters. We define the temperate or normal environment for each parameter as where the middle 90% of where people live currently, with 5% at each extreme. New locations then extend one or more of the parameters beyond the temperate range. Specific locations will not be chosen until later. For now, we identify location groups, which will have multiple specific locations. Each location helps support itself, interacts with previous locations and the rest of civilization, and helps build the next location when able to.
- Temperate Earth - Where 90% of people currently live
- Difficult Earth - 10% beyond temperate range
- Extreme Earth - from 20% beyond temperate range, to the limits of practicality
- Near Earth Space - less than 10% beyond escape energy
- Distant Space - more than 10% beyond escape energy
Level 4: FunctionsEdit
Each location will provide a set of functions, which can vary from location to location. The same types of functions will occur in multiple locations. For example, anywhere that humans live, they need a food supply. So it makes sense to identify a common set of functions for a generalized location, and then extract subsets for specific locations. This allows bringing together common design work for multiple locations, and reduce duplication of effort. Figure 4.1-1 is an example of such a generalized location model. It only shows the first level of functions and some of the flows which connect them.
To reach a final design for the program as a whole, we must choose the best lower level elements, and combine them in an optimal way. At this point we can only start to list the choices to be made and candidates to make those choices from. This section lists general design choices that apply across the whole program.
New vs Existing Methods
The highest level issue for production is the choice between existing production methods and new methods that include seed elements with self expansion, distributed operation, and possibly others. We will refer to the new methods as Advanced Manufacturing, and discuss it in Section 4.2. At first components that cannot be made internally have to be supplied from outside. As production capacity grows in size and diversity it can do more of it's own production internally. The goal is to lower production cost by a large factor by not requiring as much initial investment, and by extensive use of automation, robotics, and remote operation.
Functions and Seed Elements
Beyond the choice of existing vs new production methods, the question of what functions are needed in production, and what seed elements are preferred comes next. Production on Earth is very wide ranging and complex, so the choices here are not obvious. We can at least identify it as an area for more work. One way to organize the choices is between functions needed in many locations, and ones that are specific to particular locations. Figure 4.1-2 is an early version of a process flow to develop seed factories. Considerably more detail will be needed before any final choices can be made.
Other questions include:
- How well can existing technology work towards the goals of self-expansion, recycling, and automation, and what new technology, if any, is needed?
- What is the optimal sequence of seed elements? What is required in the initial starter set, vs items added later?
- How should the production output be divided between internal production growth, products for use in the program, and products for outside sale to help cover costs?
- Is production growth best accomplished by making copies of existing elements, making larger versions of them, or by adding entirely new elements which can do new processes?
- How much benefit does the bootstrap approach have over conventional manufacturing?
In addition to self-expansion, we will consider a distributed operation model rather than a traditional factory model. The latter assumes all production elements and workers are gathered in one location. The distributed model uses remote operation, automation, and robotics to relieve the need for lots of humans where the production tasks happen. This becomes more important in difficult environments, especially before local habitation is built. In order to make the choice between existing and new methods, the new ones have to be understood well enough to compare to the existing ones.
In a distributed operation model, it is not required that everything be distributed, only that it is an option. An optimized design may place multiple elements in one location, like conventional factories. When such a location includes seed elements that can expand production, we will call it a Seed Factory. In a distributed model, seed factory locations are mostly independent of where the people are. Design of items and control of the equipment can be done remotely using modern computers and communication. A few people are local for tasks that cannot be done remotely. Seed factories would first be used on Earth, where they generate income and growth, and to build the first space launch systems and payloads. Using the experience from Earth, later seed factories are placed in Earth orbit and farther locations. They are still mostly remote controlled, and used for orbital construction of platforms and vehicles, and to use local energy and materials resources from space. Humans can arrive in larger numbers once sufficient production capacity is in place and habitats are built. You will still need to deliver specialty items from Earth, but the bulk of supplies should come from local sources.
Temperate Earth LocationsEdit
Earth to Orbit TransportEdit
Initial Transport to Orbit
Some of the program goals and requirements require access to space, and space is a difficult environment which drives technology advances that later can be applied to the bulk of civilization on Earth. Therefore there is a need for transport capacity to and from Earth, in addition to transport among Earth locations. The question then arises how to get initial access to orbit. The choices are to buy transport on other launch vehicles, or to build our own within the program. 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.
Expansion ETO Transport
The program will add expanded 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.
Difficult Earth LocationsEdit
Extreme Earth LocationsEdit
Near Earth SpaceEdit
Near Earth ProductionEdit
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.
Orbital Mining Function
Extracting local raw materials, also called mining, should reduce cost and increase efficiency. 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. This includes:
- Mining the Earth's atmosphere from orbit using a compression scoop.
- Mining and salvage of debris and hardware in Earth orbit.
- Retrieval of raw materials from the nearest asteroids
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.
Although the Moon is physically close, Lunar surface development will likely be postponed to a later step. The reasons include lack of a gravity well to climb up and down, 100% sunlight available, and ore quality. The Lunar surface has been well mixed by impacts over time, so does not present separated compositions like the asteroids do. A more complete comparison needs to be done to validate these reasons and see how use of the Moon fits into the overall program sequence.
Materials Processing Function
This is the conversion of raw materials to finished supplies or stock materials. Section 4.9 - Processing Factory looks at the alternatives and options for this task. It will likely happen at multiple near-Earth locations, wherever it is most efficient for a given process. Options include:
- Air processing: aboard the scoop ship, or at the low orbit assembly station.
- Asteroid processing: in place at the asteroid, a high orbit near Earth, or lower orbit.
Asteroid processing nominally is started as another set of seed elements, delivered by electric tug to the desired orbit. When fully built up it converts raw materials to a varitety of useful inventory such as fuel, oxygen, structural metals, etc. This reduces the need to supply everything from Earth. Like other seed elements, it helps expand itself, makes an increasing range of parts. 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 set of alternative selections will be for which specific processing flows are to be used under what conditions.
Parts Production Function
Near Earth HabitationEdit
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. As noted above, some production methods work better with acceleration, and some agriculture may turn out to work best with gravity. So an artificial gravity level will likely be needed.
Another open question is the growth path for the habitats: 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 the known questions as a starting point.
Near Earth TransportEdit
Electric thrusters 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. 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 the orbital 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 the next step.
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.
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.
The Moon is relatively close in physical distance, but the Moon's surface requires significant additional energy to reach due to it's gravity well. Therefore it falls into the distant location category. 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.
People often neglect that the space between major planets is not empty. Section 4.12 - Interplanetary Development looks at concepts to use this space. Rather than treat it as something to be crossed as quickly as possible, we instead build transfer habitats in orbits between, for example, 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 are 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 growing network of Skyhooks provides fast velocity changes for people and cargo that needs it, while electric tugs do slower deliveries of bulk items.
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, 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.
The early phases (I to III) of the program may not even reach Mars, let alone go beyond it. Despite that, Section 4.14 - Later Projects looks at some speculative ideas for later projects. Since technology changes over time, it is not worthwhile to make very definite 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 ones developed later can be incorporated into updated program plans.