Advanced Power Sources for Space Missions (1989) / Chapter Skim
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3. Space Power Systems Options and Selection Constraints
3. Space Power Systems Options and Selection Constraints
Pages 24-51
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From page 24... ...
, dynamic isotope power sources (DIPS) , and nuclear reactor systems (see Figures 3-1, 3-2, and 3-3~.
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From page 25... ...
* Open-cycle systems raise the question of effluent impacts on the spacecraft, sensors, weapon systems, and on the power system itself #The committee did not consider this option in detail FIGURE 3-1 A nonnuclear orbital power source.
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* PER refers to Pebble bed Reactors and Particle bed Reactors, which are distinguishable from each other by the size of their fuel elements FIGURE 3-2 A nuclear orbital power source.
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From page 27... ...
Requires microwave beam to orbit Han added benefit might ensue, since this military requirement could -- as a spinoff -- lead to a true second-generation, fail-safe reactor for civil applications FIGURE 3-3 G round-based power. TABLE 3-1 Space Power Options for Each SDI Power Mode Power Mode Operational Option No Effluent Effluent Housekeeping Solar, RTG, DIPS, nuclear reactor, ground-based source Alert Burst None Solar-dynamic, None nuclear reactor Nuclear reactor Chemical, nuclear reactor .
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From page 28... ...
If a nuclear reactor is used in a multimegawatt space power system, then unlike a low-power system such as SP-100 the mass of the radiators, rather than the mass of the reactor and its shield, is the dominant component of the mass of the overall power system. Although chemical energy heat sources appear attractive because they offer rapid response and reasonable mass for limited duration, they emit effluents that may have unacceptable impacts.
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From page 29... ...
Although activation of a chemical heat source can be rapid, it may be more difficult for a fission reactor to reach full power quickly. Consequently, substantial housekeeping power may be required to maintain the power conversion cycle components in a warmed-up condition ready for rapid start-up.
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From page 30... ...
Chemical power generation systems may also emit water or other reaction products, although these products could conceivably be condensed and stored on board. Presently it is unclear whether any or all of these effluents can be tolerated by SDI systems; however, the effluent question is clearly an important consideration in choosing between effluent-em~tting and closed-cycle nonnuclear power systems for space applications.
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From page 31... ...
This solar collector and its heat receiver also require fairly accurate orientation toward the sun, an acceptable pointing error being perhaps 1 to 3 arc-minutes. Rankine, Brayton, and Stirling power conversion cycles have been proposed for use with solar energy sources.
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Considerable technology relevant to this application is available from the extensive technical experience derived from using stored propellants aboard the Titan rocket and aboard spacecraft used during the Apollo program. Nitrogen tetroxide (N2O4)
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From page 33... ...
Because of this substitution, an MHD generator may be less massive than a conventional generator, hence MHD generators have some prospect for reducing the mass of space power systems, especially for burst-power applications requiring peak powers measured in multimegawatts. In practice, introducing MHD technology poses several practical problems in addition to its extremely high operating temperatures and the need to obtain adequate electrical conductivity.
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From page 34... ...
in space, but has never employed nuclear reactor power systems for space applications except for a short-term test of the SNAP-IDA power system in 1965. In contrast, the USSR has continued to develop and deploy fission reactor systems that have been largely successful, although two unplanned reentries of Soviet nuclear-reactor-powered satellites have occurred, causing adverse public reaction throughout the world.
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From page 35... ...
The committee believes that there are earth-orbital and lunar surface applications for which nuclear power can be an important and sometimes unique option. For example, Figure 3-4, from a NASA internal study (1988)
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From page 36... ...
The six general categories of nuclear power sources (Figure 3-2) considered here are as follows: radioisotope thermoelectric generators, dynamic isotope power sources, the SP-100 class nuclear fission reactor, small nuclear fission reactors, and power sources using advanced nuclear processes.
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From page 37... ...
. In a broader sense, overall safety contingencies that must be satisfactoriTy addressed for a space nuclear system include inadvertent or uncontrolled criticality; protection of the biosphere; protection of occupational workers, astronauts, and the general public against radiation and toxic materials; safeguarding nuclear materials against diversion; disposition at the end of its useful life; compliance with domestic and international law; and achieving public acceptancethat is, the perception that all of the above issues have been handled honestly and reasonably.
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From page 38... ...
If a mission requires a nuclear-reactor power system aboard a spacecraft in a lower orbit, the reactor must be boosted to a nuclear-safe orbit after mission completion. The Soviets have launched about 35 nuclear space reactors relying on this approach.
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Radioisotope Thermoelectric Generators Radioisotope thermoelectric generators have been demonstrated to be useful and reliable power sources to supply a few watts to a few kilowatts of power for space missions. Heat is provided by radioactive decay of plutonium 238 (Pu-238)
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From page 40... ...
SP-100 Space Nuclear Reactor System The only U.S. nuclear fission reactor system that has been developed and tested in space, SNAP-1OA, consisted of a NaK-cooled 43-kWt reactor with thermoelectric power conversion, and produced 0.56 kWe.
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From page 41... ...
Considerable operational experience with N~one percent Zr had been obtained from the previous space nuclear reactor system program. Although higher operating temperatures would be desirable, the creep strength of Phone percent Zr decreases at temperatures significantly above 1450°K.
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From page 42... ...
Additional delay in implementing a space nuclear reactor power system program will of course add to the time needed for planning and deployment of an associated space mission. The dilemma is that the development time for such a system still significantly exceeds normal mission-development time, yet a candidate power system must be fully demonstrated to be feasible, reliable, safe, and acceptable to the general public, legislative bodies, and regulatory agencies before any space mission planner can count on utilizing the system as a power source.
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From page 43... ...
Power sources for the two burst-power regimes probably correspond to closed- and open-cycle systems, respectively. Tests are being conducted with two candidate technologies: incore therm~onics and the gas-cooled pebble/particle bed core.
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space nuclear reactor power system currently exceeds the time required to plan and deploy a space mission dependent upon that power source. Conclusion 7: A space nuclear reactor power system, once available, could serve a number of applications for example, in NASA and military missions req~ir~g up to 100 kWe of power or more in addition to SDI.
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From page 45... ...
Solving this problem would necessitate using some combination of multiple ground-based transmitters and spacecraft storage of electrical energy. The received electromagnetic energy would be used to charge an on-board energy storage device (e.g., batteries, superconducting magnetic energy storage)
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ENVIRONMENTAL CONSTRAINTS INFLUENCING THE SELECTION OF SPACE POWER SYSTEMS The Natural Space Environment The natural space environment contains neutral gases, plasmas, radiation (both penetrating particles and solar electromagnetic) , magnetic fields, meteoroids, and space debris.
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From page 47... ...
The lower-energy constituents of the space environment, notably neutral particles, plasmas, and fields, can be dramatically perturbed by the presence and operation of space systems, creating a local environment much different from the natural one. The impact of system interactions must be examined in the context of the local space environment, leading to results that will, of course, be system-dependent.
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From page 48... ...
For example, if space platforms were hardened to several calories per square centimeter, the substantial armor shell employed would provide an environment that may eliminate the possibility of electrical breakdown between bare electrodes and at the same time protect against effluents and space debris. Thus, responding to survivability needs could also serve these two additional purposes.
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From page 49... ...
In addition, attaining survivability against hostile threats may complicate implementation of the exposed highvoltage approach, since direct use of the space vacuum as an external surface insulator will be precluded for those space platforms that must be hardened by encapsulation to withstand hostile threats. In the SPAS studies examined by the committee, open-cycle space power systems are tentatively regarded as attractive choices compared to closed-cycle power systems because of their potential to be significantly less massive.
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From page 50... ...
One is to explore development of effluent-tolerant systems; the other is to explore using space as a "vacuum insulator," if this approach is consistent with achieving survivability against hostile threats. The two are antithetical, as an effluent-tolerant system must be carefully insulated for the long term, while a space-vacuum-insulation approach may be intolerant of effluents.
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From page 51... ...
can cast some light on impacts of effluent dump rates projected for SDI systems. Conclusion and Recommendation Based on the preceding, the committee arrived at the following conclusion and recommendation: Conclusion 3: The amount of effluent tolerable is a critical discriminator in the ultimate selection of an SD!
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