The workshop was directed to identify the energy an power needed to support activities in space, beyond the NASA Space Station Program, up to 2010
Solar and nuclear heat sources are the basis of the production of energy in space. In this section we address stationary systems on a space platform and on the surface of a planetary body. Energy sources, conversion technology, heat rejection, and the delivery of power to the user - important elements that must be considered in system design - may vary according to system use.
In this report we define the power and energy requirements of future space activity with and without the utilization of resources from space, examine existing technologies for delivering the power, and arrive at some general conclusions as to the technology research and development needed to make possible the programs envisaged.
The first scenario, shown in figure 1 [a baseline scenario graph] assumes the development of a space network with all materials and resources shipped from the Earth. A balanced development is assumed with slight increases over the current budget. the space station, which is already programmed, is used to support development in geosynchronous Earth orbit (GEO), manned exploration of the Moon, and unmanned exploration of the solar system. Eventually, beyond 2010, a lunar base and manned exploration of Mars are undertaken.
In the second scenario (fig. 2),[a baseline scenario graph] nonterrestrial resource utilization is assumed to be a goal. The paths are similar to those shown in the baseline scenario, but there is a heavier emphasis on movement to the Moon and establishment of a manned base there. Lunar materials are processed to get oxygen to support the transportation system in low Earth orbit (LEO). Selective mining of near-Earth asteroids is considered feasible. The lunar base and the production there enhance the move toward manned Mars exploration.
This section of the report includes two subsections describing "Power System Requirements" in space and the "Technologies" needed to fulfill these requirements. In the first paper, Ed Conway estimates the requirements for power to support the two scenarios, focusing on the requirements for activities at these nodes: low Earth orbit, geosynchronous Earth orbit, the Moon, Mars, and the asteroids. He identifies the appropriate technologies for each activity. Henry Brandhorst then describes the solar-energy-related technologies that may be applicable, focusing on photovoltaics and solar dynamics.
Dave Buden explores the development of nuclear power supplies for space applications. Abe Hertzberg addresses the problem of thermal management in space and describes a liquid droplet radiator. Conway discusses laser transmission of power, which if developed can influence the evolution of larger, more centralized, space power-generation stations. Finally, Bradhorst discusses the implications of space power development for the missions to be carried out within the two broad scenarios; he advances the recommendations of the workshop in this area.
Edmund J. Conway
We estimated the electrical power required for each mission in the baseline model (fig.1) [a baseline scenario graph] and in the alternative model (fig.2) [a baseline scenario graph] according to the specific energy-using activities and operations shown. We then identified appropriate technologies to meet these power requirements , using such criteria as, Can the technology fully meet the requirement? and, Can the thecnology be ready at least 5 years before the mission? In some cases, there were competing technologies for the same mission.
Low Earth Orbit (LEO)
The initial space station, scheduled for the mid- 1990s, will have 75-300 kW (electric) of continuous bus power. Mid - to late 1980s' solar photovoltaic technology is the only proven power-generating option available. However, solar photovoltaic systems require large arrays and consequently produce substantial drag. to provide power above the 75-kW level, two technologies could compete: solar dynamic (solar thermal with Stirling-, Brayton-, or Rankine-cycle conversion) and nuclear thermal (with thermoelectric, thermionic, or dynamic conversion). Both technologies are now in developmental phases.
A second-generation space station appears in the baseline model at 2008. It would be needed for large-scale space processing of terrestrial materials. Space Station 2 would require from one to tens of megawatts. Such a mission would provide a major pull on the power generating technologies. the current choice would appear to be some type of nuclear power system.
For power requirements above 1 megawatt, serious technology issues also arise in electrical power management (high voltage and current) and thermal management (how to dispose of 1 MW of low-temperature heat). Electrical power management would require both a new philosophy and some new technology. Thermal management would require such new technology as a large liquid droplet radiator.
Geosynchronous Earth Orbit
By the late 1990s, a geosynchronous experimental science platform would require up to 10 kW. this requirement could be met by solar photovoltaic power. Advanced lightweight power generation and storage systems might be required if the present limitations on payload mass to GEO have not been eased significantly. Such systems, including those with gallium arsenide solar cells in high specific-power chemical storage, are in research stage now.
By 2004, a GEO shack or temporarily inhabited repair shop on the platform will allow for human-tended and interchangeable experiments. To operate in the repair shop, the human tenders would need additional power, on the order of 10 kW. This power could be supplied by the visiting spacecraft. Solar photovoltaic technology, similar to that already mentioned for the platform, could be used.
A manned GEO station could be required beyond 2010. the power level anticipated and the enabling technology are similar to those of the LEO growth space station. Thus geosynchronous Earth orbit provides no new power challenges.
An orbital lunar mapper in the mid - to late 1990s has only small power requirements, which can be met by 1980s' technology. An unmanned surface explorer (compare (fig. 3) [Lunar Rover used on the Apollo 17 Mission] , beginning in 2004 would require only a few (2-5) kilowatts continuously, for movement, surface coring, analysis, and telemetry. A radioisotope generator (compare fig. 4) [a radioisotope thermoelectric generator] with dynamic conversion is the technology of choice.
By 2010, a lunar camp , to be inhabited only during the 2 weeks of lunar day, wold initially require 25 kW, supplied by a solar photovoltaic system. this initial power level could be augmented during future visits using similar or improved photovoltaic technology. Or the lunar camp's power system could grow, in the same manner as that of the space station, to include solar dynamic or nuclear supplies. the initial power level is suitable for crew life support, lunar science, and light work, but it does not provide the storable energy for heat and life support during the lunar night. For full-time habitation, the camp and later the base would rely on nuclear power supplying a few hundred kilowatts. (See the analogy in figures 5a [Spartan Lunar Base] and 5b.) [South Pole Station] High power requirements away from the base for transportation or mining could be supplied by a separate source or by transmission. Point-to-point beamed transmission along the surface and space is possible.
The baseline and alternative scenarios identify only one mission to Mars by 2010, the Mars sample return. This mission would require only very limited power, which could be provided by current technology - a radioisotope thermoelectric generator. the later Mars site survey rover would have power requirements similar to the lunar surface explorer (2-5kW) and, like it, would rely on a radioisotope generator with a dynamic converter. (See figure 6.) [Unmanned Mars Lander]
The alternative model (fig. 2) [a baseline scenario graph] includes unmanned exploration of an asteroid beginning in 2005. This involves activities and power requirements similar to those for the earlier lunar surface explorer and could be handled by a similar system. Mining (not included in the scenario) would require power on the order of 10 MW. A nuclear reactor power system developed for general application to industrial processing in space would be utilized. See figure 7 [Phobos Deimos Hot Drill] for a medium-range application on one of the asteroid-like moons of Mars.
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