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Executive Summary This study focuses on approaches to satisfying the power require- ments of space-based Strategic Defense Initiative (SDI) missions. The study also considers the power requirements for non-SDI mil- itary space missions and for civil space missions of the National Aeronautics and Space Administration (NASA). The more demand- ing SDI power requirements appear to encompass many, if not all, of the power requirements for those missions. Study results indi- cate that practical fulfillment of SDI requirements will necessitate substantial advances in the state of the art of power technology. SDI goals include the capability to operate space-based beam weapons, sometimes referred to as directed-energy weapons. Such weapons pose unprecedented power requirements, both during prepa- ration for battle and during battle conditions. The power regimes for those two sets of applications are referred to as alert mode and burst mode, respectively. Alert-mode power requirements are broadly stated, inadequately defined, and still evolving. They are presently stated to range from about 100 kw to a few megawatts for cumulative durations of about a year or more. These power and time parameters correspond to an energy (power multiplied by time) requirement in space ranging from about a million kilowatt-hours to several billion kilowatt-hours. Burst-mode power requirements are roughly estimated to range from tens to hundreds of megawatts for durations of a few hundred to a few 1

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2 ADVANCED POWER SOURCES FOR SPACE MISSIONS thousand seconds, corresponding to space-based energy requirements ranging from hundreds to millions of kilowatt-hours. Complete study findings, conclusions, and recommendations are contained in the body of this report and are compiled in Appendix E. This summary restates all of the study recommendations and highlights the most significant study conclusions that led to them. Those conclusions are that: . There are two likely energy sources, chemical and nuclear, for powering SDI directed-energy weapons during the alert and burst modes. The choice between chemical and nuclear space power sys- tems depends in large part on the total duration during which power must be provided. On the basis of mas~e~ectiveness, large durations favor the nuclear reactor space power system and short durations fa- vor chern~cal power systems if their effluents can be tolerated. For alert-mode requirements at the low-power end of the requirement range stated above, a solar space power system might qualify. ~ Multimegawatt space power sources appear to be a necessity for the burst mode. Pending resolution of effluent tolerability, open-cycle power systems (systems whose working fluid is used only once) appear to be the most mass-effective solution to burst-mode electrical power needs in the multimegawatt regune. If an open-cycle system cannot be developed, or if its interactions with the spacecraft, weapons, and sensors prove unacceptable, the entire SDI concept will be severely penalized from the standpoints of cost and launch weight. . A nuclear reactor power system may prove to be the only viable option for powering the SDI burst mode (if effluents from chemical power sources prove to be intolerable) and for powering the SDI alert mode (if the total energy requirements of the alert mode exceed what can be provided by chemical or solar means). ~ A space nuclear reactor power system, such as the SP-100 system presently being developed, would be a step toward meeting SDI requirements and would be applicable to other civil and military space missions. Early deployment of an experimental space power system, possibly the SP-100 system, would be useful to provide confirmation of design assumptions prior to commitment to an SDI system. ~ Beaming power upward from earth by microwaves or lasers has not been extensively explored as a space power option, but may be worthy of further study.

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EXECUTIVE SUMA~4RY . 3 Estimated gross masses of SDI space power systems ana- Tyzed in existing studies appear unacceptably large to operate major space-based weapons. At these projected masses, the feasibility of space power systems needed for high-power SD! concepts appears impractical from both cost and launch considerations. . At the current rate of power technology development, power systems appear to be a pacing item for the successful development of SDI directed-energy weapon systems. Accordingly, either major innovations in power systems and power system components will be required or SDI power requirements wiD have to be relaxed. ~ Existing SDI space power architecture system studies do not provide an adequate basis for evaluating or comparing cost or cost- effectiveness among the space power systems ebonized, do not ade- quately address questions of survivability, reliability, maintainability, and operational readiness, and do not adequately relate to the design of complete SDI spacecraft systems. The committee arrived at the following recommendations: Recommendation 1 (Chapter 4~: Using the latest available in- fonnation, an in-depth, full-vehicle-eystem preliniinary design study- for two substantially different candidate power systems for a common weapon platform Should be performed now, in order to reveal secondary or tertiary requirements and limitations in the technology base that are not readily apparent ~ the current Mace power architecture system studies. Care should be exercised in estate fishing viable technical assumptions and performance requirements, including survivability, maintainability, availability, ramp-rate, voTt- age, current, torque, effluents, and so on. This study should ca~effflly define the available technologies, their deficiencies, and high-leverage areas where investment will produce significant improvement. The requirement for both alert-mode and burst-mode power and energy must be better defined. Such an in-depth system study wiR improve the basis for power system selection, and could also be helpful in rip e e e e re 1nmg mission requirements. Recommendation 2 (Chapter 3~: T~ remove a major obstacle to achieving SD! burst-mode objectives, estimate as soon as practicable the tolerable on-orbit concentrations of effluents. These estimates should be basedto the maximum extent possible~n the results of space experiments, and should take into account impacts of effluents

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4 AD VANCED PO WER SO URGES FOR SPA CE MISSIONS on high-voltage insulation, space-platform sensors alla weapons, the orbital environment, and power generation and distribution. Recommendation 3: Rearrange space power R&D priorities as follows: a. (Chapter 3) Give earn, careful consideration to the regula- tory, safety, and National I:n~rironmental Policy Act requ~re- mente for space nuclear power systems from manufacture through launch, orbital service, safe-orbit requirements, ~~d disposition. b. (Chapter 6) The SP-100 nuclear power system is applicable both to SD] requirements and to other ciao and military space m~sione. Therefore, SP-100 development should be completed, following critical reviews of SP-100 performance goals, design, and design margins. c. (Chapter 6) SD! buret-mode requirements exceed by one or more orders of magnitude the ~naxmmm power output of the SP-100. Therefore, both the nuclear and nonnuclear SD! multimegawatt programs should be pureed. Hardware development should be coordinated with the results of imple- menting Recommendation 5. Recommendation 4 (Chapter 6~: Consider deploying the SP- 100 or a chemical power system on an unmanned orbital platform at an early date. Such an orbital "wall sockets could power a number of scientific and engineering experiments. It would concurrently provide experience relevant to practical operation of a space power system similar to systems that might be required by the SDI alert and burst modes. Recommendation 5 (Chapter 5~: Make additional and efEec- tive m~estments now in technology and demonstrations leading to advanced components, inclu~mg but not limited to: themal management, Aching radiators; materials structural, thermal, environmental and supercon- ducting; electrical generation, conditioning, switching, trane~nission, and storage; and long-term cryostorage of H2 and O2. Advances in these areas will reduce power system mass and

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EXECUTIVE SUMMARY s environmental impacts, improve system reliability, and, in the long term, reduce life-cycle power system cost. Recommendation 6 (Chapter 3~: Review again the potential for ground-based power generation (or energy storage) with subsequent electromagnetic transmission to orbit. Recommendation 7 (Chapter 2~: After adequate evaluation of potential threats, further analyze the subject of Vulnerability and survivability, mainly at the overaD system Ievel. Data resulting from implementing Recommendation 1 would be appropriate for this further analysis. Pending such analysis, candidate power systems should be screened for their potential to satisfy interun SDI Orga- nization (SDIO) survivability requirements, reserving judgment as to when or whether those requirements should constrain technology development. Convey the screening results to the advocates of those candidate power systems, to stimulate their finding ways to enhance survivability as they develop the technology. Recommendation 8 (Chapter 6~: TD further U.S. capabilities and progress In cnU as well as military applications of power tedh- nology, both on the ground and In space, and to maintain a rate of progress In advanced technologies adequate to satisfy national needs for space power, plan and implement a focused federal pro- gram to develop the requisite space power te~mologies and systems. This program based on a multlyear federal commitment shown be at least as large as the present combined NASA, Department of Defense (DOD, including SDIO), and Department of Energy space power programs, independent of the extent to which SD! itself is funded.