Charles H. Eldred and Barney B. Roberts
This section of the report provides a collection of alternative scenarios that are enabled or substantially enhanced by the utilization of nonterrestrial resources. Here we take a generalized approach to scenario building so that our report will have value in the context of whatever goals are eventually chosen.
One significant finding of this workshop is that to discuss only tangible materials from asteroids or the lunar surface is probably too limiting an assumption to permit consideration of all viable scenarios. Thus, although we decided to discuss the following space resources, we realize that this list is nonexhaustive.
Space Resources
Tangible Materials
Lunar materials: The foremost lunar resource we identified was lunar oxygen for rocket propulsion (see fig. 3). The Moon can also be a source of metals (iron, aluminum, magnesium, titanium) and nonmetals (glass, ceramics, concrete), which may find use as structural or shielding materials on and off the Moon. The Moon is relatively deficient in some of the more volatile elements hydrogen, carbon, and nitrogen.
Asteroidal materials: Earth approaching asteroids are rocky bodies that can provide useful materials, including some elements not found in abundance on the Moon. Some asteroids contain substantial quantities of water and carbonaceous material; others have abundant metal, including iron, nickel, cobalt, and the platinum group (see fig. 4). Some asteroids are energetically more accessible than the lunar surface; however, trip times are generally long and low-energy opportunities limited. For this reason, these asteroids don't offer convenient staging points.
Martian materials: The utilization of martian resources, particularly to produce propellants, is a probable aspect of an intensive Mars exploration program. Propellants could be extracted from Mars' atmosphere or from materials on the surface of Mars, Phobos, or Deimos (see fig. 5). These satellites have characteristics of carbonaceous asteroids and for many purposes, including access, may be considered as asteroids.
Vacuum
Vacuum, used in many scientific experiments and manufacturing processes, is expensive to create and limited in volume on Earth. Workshop participants were not convinced that going into space to utilize the vacuum would lead to economic benefits, considering the high cost of space transportation today. However, the potential of the limitless vacuum available in space kept it on the list as a viable resource. The unlimited vacuum could enable new analytical or testing procedures that depend on the surface properties of materials or the transmission of molecular beams. The vacuum of space could enable accelerators with no need, or a substantially reduced need, for containment devices. Such vacuum might permit new uses of the metals sodium and potassium, which are difficult to handle in the Earth's atmosphere. And it could allow the high-temperature vacuum processing of glasses, metals, and cement.
Energy
Energy from space has been of practical use for many years. The primary energy source is of course the Sun. The most prominent application is solar photovoltaic power for satellites now in orbit. In the state-of-the-art process, solar cells directly convert incident solar energy into electrical energy. The advantages of collecting solar energy in space rather than on Earth arise principally from two facts: The first is that one can get more solar energy by choosing an orbit that has more "daylight" hours, and the second is that one can avoid interference from the atmosphere.
Energy from space may be utilized in space to power facilities (including those on the surfaces of planetary bodies) or can be returned to Earth for conversion to electrical energy. Alternatively, the Sun's energy may be used directly. The propulsive power of solar photons may be used to drive a solar sail. Direct use of thermal energy to provide process heat may be important in space. The Sun's light could be reflected, selectively, to the Earth to light cities, agricultural areas, or arctic night operations (see fig. 6).
Large space facilities, such as the space station or a lunar base, will require significant power (see fig. 7). The power requirements for the current space station configuration are so large that the structural design and control system requirements will be driven by the solar panels if photovoltaic devices are used. A competing design concept being considered is solar dynamic (see fig. 8). This approach would use an energy-focusing mirror and a heat engine to drive a generator. Another approach would use electrodynamic tethers to exchange orbital energy for electrical energy. This very efficient process may be useful in low Earth orbit for energy storage but could not produce the high power levels needed for the primary supply system.
Several NASA and privately funded efforts have been undertaken to define ways in which space supplied energy might be used to replace energy from nonrenewable Earth-based resources. One of these was the solar power satellite (SPS) system, which would ring the Earth in geosynchronous orbit with 5- by 20-kilometer solar powered satellites designed to microwave the energy to the Earth. Another proposal for supplying power from space to the Earth uses large areas on the Moon for relatively low-efficiency photovoltaic devices utilizing indigenous lunar material, such as silicon. The lunar power station would also transmit energy to Earth by microwave.
The Sun's energy is a perpetual source of clean, nonpolluting power, and major technological advances in photoconversion and energy transmission could substantially alter any space scenario.
Low to Negligible Gravity
Many manufacturing processes may be enabled or improved by the utilization of the low to negligible gravity of space. An electrophoresis process for separating cells having small differential charges is being developed by private industry. In the absence of gravity, an electrical field can cause the desired cells to migrate toward a collector. The great selectivity of this process and the purity of its products may lead to drugs effective in the treatment of cancer, diabetes, and other diseases (see fig. 9). Other processes may produce new alloys, high strength glasses, and more efficient semiconductors. The more space transportation costs are reduced, the wider the range of economical microgravity processing will be. This is an area of potentially significant commercial investment.
Physical Location/View
Physical location in space and the view from off the Earth have shown themselves to be a resource of great benefit to the public (see fig. 10 and fig. 11). The particular characteristics of the geosynchronous orbit, both from the standpoint of view (weather satellites) and from the standpoint of stability (communication satellites), have been heavily exploited and have provided substantial benefits in revenue and in public safety. Significant public and private (as well as joint venture) technology developments are under way to further utilize this unique space resource for communication, navigation, search and rescue, and other purposes. The location of astronomical facilities in space has been demonstrated to be of fundamental scientific importance (see fig. 12). Another potential utilization of location/view would be for recreation in low Earth orbit. Studies have shown that a market does exist for the public to use space as a recreational area, if transportation costs can be made affordable.
Other potential developments in the cultural and societal arena are certain to appear but difficult to quantify. Historical evidence suggests that humankind always modifies its culture and societal norms to adapt to major alterations of its sphere of influence. It is conceivable that artistic and sporting activities could find a role in space and may be marketable.
By way of concluding this section on space resources, we, the members of the workshop, want to stress that the list of space resources is not limited to those we have mentioned. Other usable resources might be isolation (for nuclear waste disposal or very hazardous research projects) and extreme temperature gradients (for heat engines).
Generic Scenarios for Utilization of Nonterrestrial Resources
In order to suitably characterize the future utilization of nonterrestrial resources, we should assess scenarios broad enough to bring to the surface all or most of the key technology issues. The exploitation of nonterrestrial resources encompasses a very broad range of potential products, benefits, resources, supporting systems, and technology requirements. The evolution of space activities into the 21st century also holds the potential for a much changed mix of space users, with increased levels of commercial, international, and military space activities. The objective of this section of the report is to view the broad range of mission alternatives that may use space resources and to select a few examples that illustrate a mix of mission characteristics.
Mission Characteristics and Options
Table 1 illustrates the variety of options that are possible for future missions. Most missions can be described by one or more of the options related to each item. Therefore, a specific mission can be characterized by a total set of option choices.
| Item | Options* | |||
|---|---|---|---|---|
| 1. Goals: | Leadership Exploration Human spirit | Public applications | Commercial |
Security Military |
| 2. Participants: Type Countries: | Government National | Government International | Commercial |
- |
| 3. Purpose: | Science/research | Enhanced mission | Valuable product | Prestige/power |
| 4. Space resource: | Materials | Vacuum/Energy | Gravity | Location/view |
| 5. Resource location: | LEO GEO | LEO/cislunar (debris expendables) | Lunar Asteroidal | Planetary (Mars & moons) |
| 6.Product: | Materials Volatiles Low value solids High value solids | Information/data | Energy | Pleasure |
| 7.Processing: Location Type | in situ None | LEO Automated | Other Manned |
- |
8.Transportation: Mode: | Same Chemical rocket | in situ processing/ used elsewhere Aerobrake | Intermediate site Other |
At use site |
| 9.Infrastructure: | Earth-to-orbit transportation Orbital transfer vehicles | LEO space station | Observation instruments | Planetary bases or outposts |
*The columns in this table do not represent related categories but are used simply to enumerate options for each other.
Mission goals: Four broad goal options are shown. The identification of relevant goals is imperative to advocacy of the overall program and its technology requirements. Each of the goals represents a valid component of the total space program. Although some goal from the leadership/ human spirit class may be the only goal of a specific mission, most space missions have been dominated by a strong set of scientific or applications goals. Such human goals can often be attained with only marginal costs when added to more concrete goals.
Participants: The mix of participants in space activities is rapidly changing from the historical dominance of the U.S.A.'s civilian space agency and the more military space effort of the U.S.S.R. In the United States, military funding of space activities now exceeds that of NASA. The U.S. program is encouraging commercial participation. And most of the advanced countries and many developing countries are pursuing space capabilities to increase their military options, to advance technology, and to gain prestige. These developments may drastically change the way in which space activities are pursued in the 21st century. It will be necessary for the nations of the world to agree on policies for the utilization of space resources because they are limited. Already at issue are the filling of geosynchronous Earth orbit and the problem of orbital debris.
Purpose: Use of space resources spans a range of purposes from pure science (planetary observations) through mission enhancement (such as in situ propellant production) to the production of products with value to a third party. National prestige and the development of new technology have been strong motivators of national space programs.
Space resource: the details of indigenous space resources have been discussed earlier in this section. We consider materials placed in space for one purpose and then recycled for another to be a special category of space resources.
Resource location: the location of the resource has tremendous implications for the transportation requirements of the mission and for the possibility of human participation. One early exploitation of space material resources may be the scavaging of Space Shuttle cryogenic propellants and external tank materials, which are potentially available in low Earth orbit. The development of resources on planetary bodies (Moon, Mars) is considered essential to any longterm activities there.
Product Products of value include not only materials but also energy, information (as with communication satellites), and possibly pleasure and entertainment (as represented by tourism and national parks).
Processing: The process for converting a raw resource into a valuable product, the location for this process, and whether or not humans are directly involved in the process are key considerations.
Transportation: Transportation between key locations, which include the operations base, the resource site, the processing site, and the use site, is one of the major factors in feasibility and achieving favorable economics. The transportation strategy, the transportation system and the transportation technology level are key issues in this set of tradeoffs.
Infrastructure: The activities of each chosen mission will require that a set of facilities be established in space. These facilities will be a subset of this general set:
Selected Missions
Four mission examples are shown to illustrate the variety of options in the various areas listed in the previous subsection. These four missions are not intended to be all encompassing; readers are encouraged to use table 1 to create and characterize other missions of interest.
Mission 1 - lunar or asteroidal propellant extraction; Table 2 and figures 13 and 14 illustrate the characterization of these missions, which are combined because of a high degree of similarity. Such a mission has many attractive features. It has a combination of goals, including elements of both exploration and commercialization, with a probable evolution from exploration to commercialization. Participants could combine government and private investment. The product could be used to enhance the basic mission in the early phases and provide a valuable output in the later phases of the program.
Development of the processing systems and transportation systems are key technology challenges. The infrastructure supports growth to exploitation of solid materials and can complement military technology requirements.
Mission 2 - climate modification for agricultural productivity: Table 3 illustrates this mission, which focuses on critical world population needs for food. This program would be a cooperative international government project and would exploit the energy resources of space. Options exist for utilizing nonterrestrial materials to construct space energy facilities. Requirements for transportation to GEO would be increased under this plan. The potential for direct benefits to major portions of the world's population could motivate a large-scale effort of this type.
Mission 3 - information or entertainment: Table 4 and figures 15 illustrate this mission area, which focuses on the development of commercial opportunities in space that affect the individual person. This effect is illustrated in two ways: (1) bringing world information and communication to the individual (i.e., complexity inversion) and (2) enabling tourist-type access to space. If the much lower transportation costs necessary to enable tourism could be achieved, then the expansion of the market to the individual would enable tremendous business and economic opportunities.
Mission 4 - Strategic Defense Initiative (SDI): Table 5 illustrates a mission to support the strategic defense initiative. SDI systems could benefit from large amounts of low-grade shielding materials for systems in low Earth orbit. Although there are some areas of technology commonality with mission 1, the goals, participants, and products of interest are substantially different from those of the other missions. Also, critical tradeoffs would be decided on the basis of much different assessment criteria.
Summary: Space Resource Mission Alternatives The mission options of table 1 present the basis for the assessment of a broad range of space resource scenarios. The four example missions were selected to illustrate the variety of possible options, Issues, systems and technologies with common threads in these missions should be of particular interest to longe-range planners.
To clarify the technology issues associated with this broad range of possible goals, we developed in greater detail two variants of the first goal, lunar or asteroidal propellant extraction. We chose to develop these two scenarios because they are driven by the utilization of space resources rather than merely augmented by the availability of such resources. Because of the focus of these scenarios, we expected their technological requirements to be clearer. The first alternate scenario (fig. 16) emphasizes lunar and asteroidal resource extraction, with manned Mars missions as a long-term objective. The second alternate scenario (fig. 17) follows a broader developmental strategy that places less emphasis on lunar and asteroidal propellants and more emphasis on exploration and scientific study of the solar system.
| Item | Options | |||
|---|---|---|---|---|
| 1. Goals: | Exploration | Public applications | Commercial | - |
| 2. Participants: Type Countries: | Government National | Government/commercial International | Commercial |
- |
| 3. Purpose: | Science/research | Enhanced mission | Valuable product | - |
| 4. Space resource: | Materials | - | - | - |
| 5. Resource location: | - | - | Lunar Asteroidal | Moons of Mars |
| 6.Product: | Materials Volatiles | - | - | - |
| 7.Processing: Location Type | in situ None | LEO Automated | Other Manned |
- |
| 8.Transportation: Mode: | Same Chemical rocket | in situ processing/ used elsewhere Aerobrake | Intermediate site Other |
At use site |
| 9.Infrastructure: | Earth-to-orbit transportation Orbital transfer vehicles | LEO space station | Observation instruments in LEO & GEO |
Lunar base/Asteroidal outpost Mars base Phobos outpost |
| Item | Options | |||
|---|---|---|---|---|
| 1. Goals: | Human spirit | Public applications | - | - |
| 2. Participants: Type Countries: | Government | International | - | - |
| 3. Purpose: | - | - | Valuable product | - |
| 4. Space resource: | - | Energy | - | - |
| 5. Resource location: | GEO | - | Lunar | - |
| 6.Product: | - | - | Energy | - |
| 7.Processing: Location Type | in situ None | LEO Automated | Other Manned |
- |
| 8.Transportation: Mode: | Same Chemical rocket | in situ processing/ used elsewhere Aerobrake | Intermediate site Other |
At use site |
| 9.Infrastructure: | Earth-to-orbit transportation Orbital transfer vehicles | LEO space station | Observation instruments in LEO & GEO |
Lunar base |
| Item | Options | |||
|---|---|---|---|---|
| 1. Goals: | - | - | Commercial | - |
| 2. Participants: Type Countries: | National | International | Commercial |
- |
| 3. Purpose: | - | - | Valuable product | - |
| 4. Space resource: | - | - | - | Location/view |
| 5. Resource location: | LEO GEO | - | Lunar | - |
| 6.Product: | - | Information | - | Pleasure |
| 7.Processing: Location Type | None | - | - | - |
| 8.Transportation: Mode: | Same Chemical rocket | Aerobrake | Other |
- |
| 9.Infrastructure: | Earth-to-orbit transportation Orbital transfer vehicles | LEO space station | Observation instruments in LEO & GEO |
Lunar base |
| Item | Options | |||
|---|---|---|---|---|
| 1. Goals: | - | - | - | Security Military |
| 2. Participants: Type Countries: | Government National | - | - | - |
| 3. Purpose: | - | - | - | Prestige/power |
| 4. Space resource: | Materials | - | - | Location/view |
| 5. Resource location: | LEO GEO | LEO/cislunar | Lunar Asteroidal | - |
| 6.Product: | Materials Low value solids | Information/data | Energy | - |
| 7.Processing: Location Type | in situ None | LEO Automated | Other Manned |
- |
| 8.Transportation: Mode: | Same Chemical rocket | in situ processing/ used elsewhere Aerobrake | Intermediate site Other |
At use site |
| 9.Infrastructure: | Earth-to-orbit transportation Orbital transfer vehicles | LEO space station | Observation instruments in LEO & GEO |
Lunar base Asteroidal outpost Phobos outpost |
Impacts of Sociopolitical Conditions
