SPACE SOLAR POWER REVIEW Volume 2, Number 4, 198'
SPACE SOLAR POWER REVIEW Published under the auspices of the SUNSAT Energy Council Editor-in-Chief Dr. John Freeman Space Solar Power Research Program Rice University, P.O. Box 1892 Houston, TX 77001, USA Associate Editors Dr. Eleanor A. Blakely Lawrence Berkeley Laboratory Colonel Gerald P. Carr Bovay Engineers, Inc. Dr. M. Claverie Centre National de La Recherche Scientifique Dr. David Criswell California Space Institute Mr. Leonard David PRC Energy Analysis Company Mr. Hubert P. Davis Eagle Engineering Professor Alex J. Dessler Rice University Mr. Gerald W. Driggers L-5 Society Mr. Arthur M. Dula Attorney; Houston, Texas Professor Arthur A. Few Rice University Mr. I.V. Franklin British Aerospace, Dynamics Group Dr. Owen K. Garriott National Aeronautics and Space Administration Professor Norman E. Gary University of California, Davis Dr. Peter E. Glaser Arthur D. Little Inc. Professor Chad Gordon Rice University Dean William E. Gordon Rice University Dr. Arthur Kantrowitz Dartmouth College Mr. Richard L. Kline Grumman Aerospace Corporation Dr. Harold Liemohn Boeing Aerospace Company Dr. James W. Moyer Southern California Edison Company Professor Gerard K. O'Neill Princeton University Dr. Eckehard F. Schmidt AEG— Telefunken Dr. Klaus Schroeder Rockwell International Professor George L. Siscoe University of California, Los Angeles Professor Harlan J. Smith University of Texas Mr. Gordon R. Woodcock Boeing Aerospace Company Dr. John Zinn Los Alamos Scientific Laboratories Editorial Assistant: Edith R. Mahone Editorial Office: John W. Freeman, Editor-in-Chief, Space Solar Power Research Program, Rice University, P.O. Box 1892, Houston, TX 77001, USA.
0191-9067/81/040325-03$02.00/0 Copyright ® 1981 SUNSAT Energy Council EDITORIAL PETER E. GLASER Arthur D. Little, Inc. Acorn Park Cambridge, Massachusetts 02140, USA “It sounds like science fiction . . is the introductory statement of the July 2, 1981 News Release of the National Research Council (NRC) which heralded the publication of the National Academy of Sciences (NAS) report “Electric Power from Orbit: A Critique of a Satellite Power System,” by the Committee on Satellite Power Systems (SPS) of the NRC. This statement hardly creates an unbiased impression for discussions of the SPS concept which are necessary to clarify the potential of alternative energy conversion technologies and the role of each of these technologies in meeting the global energy challenges faced by both developed and developing countries in the 21st century. The purpose of the NRC Committee was to: • Identify critical scientific and technical issues affecting the SPS concept. • Identify gaps in the U.S. Department of Energy (DOE) and NASA SPS Program. • Examine the results of the SPS program. The NAS report addresses the salient technical, economic, environmental and societal issues but arrives at conclusions which are not in accord with the knowledge gained in the DOE/NASA SPS program and which do not follow from the statements in the report itself. The following quotations from the NAS report pertaining to the DOE/NASA program, SPS reference system, the forecasts of technology advancement and the alternative energy conversion technologies indicate that the report can be interpreted in ways which would lead to a more positive view of the SPS concept and perceptions regarding its overall feasibility. The NAS report concludes that DOE and NASA performed a thorough study of the SPS concept, and that the study provides a “tremendous amount of information useful for policy making.” The major conclusion of the report, however, is that “. . . no funds should be committed during the next decade to pursue the development of an SPS.” Since the DOE/NASA program outlines a research program designed to obtain information on technical, economic, environmental, and societal issues, the clarification of these issues is a prerequisite to a decision regarding the development of the SPS. The report does acknowledge that ”... some type of SPS would be technically possible if costs were not a consideration,” and admits that “Fusion — has yet to be shown to be technologically feasible.” The NAS report focuses on the SPS reference system which was evolved by NASA as a “tool for inquiry,” rather than a design for an SPS which would actually be constructed. Furthermore, the NASA SPS reference scenario, which assumed
that 60 satellites would be constructed between 2000 and 2030, was not a plan or a prediction of what will or should happen, but a basis for studies pertaining to space transportation, material resources, and manufacturing requirements. The report comments correctly that unless the cost of an SPS is competitive with alternative energy conversion technologies, it “simply would not be built." Therefore, the statement that the price tag for the SPS reference scenario will be in the range of 3 trillion dollars lacks economic justification. There is no basis for projecting the costs of 60 SPSs to be constructed 30 to 50 years hence without accounting for the evolution of advanced technologies, including low-cost, efficient, space-qualified solar cells; low-cost space transportation systems from Earth to low Earth orbit, and from low Earth orbit to geosynchronous orbit; space construction techniques; and technologies associated with the transmission of power from space to Earth. Alternative energy conversion technologies, whether based on development of coal, fast breeder, or fusion power plants, must also achieve a competitive cost range, or such technologies would not be commercialized on the scale projected. The finding that single crystal silicon cells will be too expensive for use in the SPS is moot because more advanced photovoltaic materials for thin film solar cells are projected to be available by the end of this decade.* Gallium .arsenide solar cells are used in an advanced SPS concept, evolved by Rockwell International, at a projected capital cost of $1500 per kW, about half that of the SPS reference system. The report states that “If constraints are placed on the use of coal or uranium (in conventional and breeder reactors) and practical fusion reactors do not achieve their goal, an SPS could become an attractive option for development in the next century," and further, "... there is a possibility that some future combination of high demand and constrained supply could make a more advanced SPS an important option in the more distant future. For the most part, building an SPS requires advances in materials and techniques in system development on a large scale rather than the discovery of new science.” Unless research is performed, how are these advances to be accomplished? Whether the most effective way to advance the SPS concept will be to perform generic research, as the NAS report recommends “where areas relevant to SPS technologies may be investigated in pursuit of goals of other programs, research should be vigorously conducted and the results evaluated for the implications on the SPS concept,” or whether a specific SPS research program to define relevant technologies and indicate ways to lower the cost of the SPS should be pursued is a matter for debate. Consideration should be given to planning the most effective SPS research program, rather than focusing on a specific design, or costs of technologies which will not be commercialized until the 21st century. The SPS option should be kept open because, as the NAS report acknowledges, “there are uncertainties concerning the availability of large-scale sources of energy for electricity beyond the early part of the next century. The use of coal is, of course, technically feasible and may set the standard for economic competition; but concerns about carbon dioxide emissions and other environmental effects could constrain coal development. The nuclear breeder reactor is also technically feasible, but it faces problems of political acceptability because of concerns about reactor safety, waste management, and the potential for proliferation of nuclear weapons. Even though advances are being made in terrestrial photovoltaic cells, the technol- *Aerospace Power Systems, R.R. Barthelemy and D.J. Curtin, Astronautics and Aeronautics, July/ August 1981, p. 71.
ogy must await progress in large-scale electrical storage capacity if it is to substitute appreciably for base load power. Fusion has a potential of substantial benefit as a long-term source, but has yet to be shown to be technologically feasible.” The NRC Committee positions on the subject of an SPS research program are indicated in the report by the following statement: “In our current circumstances the prudent course for the next few decades is to keep a variety of long-term energy options open through research or development efforts in rough proportion to their expected promise,” but the report then goes on to observe that “for SPS, whose promise is both uncertain and far in the future, periodic review and evaluation of relevant advances in related programs would serve the purpose.” The question arises, in view of the uncertainties discussed in the previous paragraph: What crystal ball has the NRC committee used? It is difficult to see how the committee concluded that no program of research on the SPS be undertaken on the basis of the report of the Working Group on Space Systems to the NRC committee which states: “We recommend that NASA continue conceptual studies on promising new SPS concepts. We recognize, however, that a meaningful SPS option will in fact be foreclosed unless sufficient research development and testing are conducted on the main elements of a future SPS to provide a basis for sound assessments of feasibility and cost.” The NAS report omitted the historic quotations which were selected by the Working Group on Space Systems to introduce sections of its report. For example, the statement “Space-travel is utter bilge” by Sir Richard van der Riet Wooley, the Astronomer Royal, 1956, preceded the discussion of the SPS “Probable Technical State-of-the-Art in the First Decades of the Next Century,” which intended to show that lack of vision is not uncommon even among renowned scientists and VIPs. Based on the information presented in the reports submitted by several of the working groups to the NRC committee (contained in the Appendix to the NAS report), and the evidence presented in the comprehensive study of the SPS completed by the DOE and NASA which, as the report indicates, was ”... a well- conceived and well-managed study in which an exhaustive number of aspects of an SPS were examined,” the NRC committee could have endorsed an SPS research program. The NRC committee report illustrates the aptness of Robert Goddard's belief: “It is difficult to say what is possible, for the dream of yesterday is the hope of today and the reality of tomorrow.” On the basis of existing information, research on the issues associated with the SPS can be justified in the broader context of a space program where the development of technologies for space transportation, space construction, and power conversion could support future mission goals represented by the SPS.
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0191 -9067/81 /0403 29-07802.00/0 Copyright ® 1981 SUNSAT Energy Council THE SOLAR POWER SATELLITE — AN OPPORTUNITY FOR THIRD WORLD DEVELOPMENT RASHM1 MAYUR and PETER E. GLASER SUNSAT Energy Council THE DILEMMA OF DEPLETING ENERGY SOURCES The multitude of challenges facing the Third World seems insurmountable. While the developed countries are getting richer, the developing countries are continuing to suffer the consequences of expanding populations, depleting resources, and grinding poverty. One of the most serious causes underlying this critical situation is the escalating prices and reduced availability of energy. The global energy situation is at the top of the agenda of contemporary society and is likely to remain of vital concern to every nation well into the 21st century. As a result, the means to deal with both the short- and long-term effects of complex energy supply and demand issues, particularly for developing countries, is engaging the attention of policy makers and is being hotly debated in public forums. The debates tend to be only between optimists and pessimists. The optimists are sure that they have a technological fix to deal with every specific aspect of the energy problem; the pessimists see in every proposed solution a plethora of unresolved risks. There is often a reluctance to pursue the arduous route of research, experiment, and compromise which can lead to practical solutions. Never has the search for new energy resources been more acute than now. Never before have so many millions of people experienced such privation and lived in misery, particularly in the Third World. In spite of massive technological developments, the gap in living standards between the industrialized countries of the North, and the developing countries of the South, has been widening. The best measure of this gap is the per capita utilization of energy, which in the developed countries is greater than in developing countries by at least tenfold. Combining per capita utilization of energy with projected population growth, the global energy demand is projected to increase fivefold during the next 50 years, which would place intolerable burdens on the global ecosystem. Conventional nonrenewable energy sources that are based on fossil fuels or uranium are unlikely to meet this unprecedented energy demand without potentially dire environmental consequences. Therefore, human ingenuity must be directed towards finding energy resources which provide hope for Third World countries to increase Presented at the United Nations Conference on New and Renewable Sources of Energy, Nairobi, 10-21 August 1981. United Nations Paper A/CONF. 100/NGO/3. Address correspondence to Frederick H. Osborn, Executive Secretary, SUNSAT Energy Council, Box 201, Cold Spring, NY 10516, USA.
their living standards and to reduce the possibility of conflicts caused by shrinking energy resources and expanding demands. If the Earth is considered a closed ecological system in which humanity is destined to live from generation to generation, the recognized limits on nonrenewable energy resources and the considerable uncertainties in achieving the global potential of known energy conversion methods could result in famines, shortages, and social upheavals, unless world population growth is drastically reduced. If not, this apocalyptic view has to be considered a distinct possibility. Countries will have to learn how to manage their affairs far more wisely if they have to rely on only nonrenewable energy resources and no one of these energy sources will by itself meet the future energy demands. Thus the search for new sources of nonrenewable fuels can only postpone the day of their ultimate exhaustion. The Third World countries are bearing the brunt of the effects of energy resource depletion and price escalation. In fact, many developing countries are facing an energy catastrophe. THE POTENTIAL OE SOLAR ENERGY There is a growing consensus that increasing reliance could be placed on renewable energy resources which have their origin in the energy radiated by the sun. Solar energy holds out the hope to the Third World that the basic needs of its people can be met and that plans for industrialization and modernization which largely rely on the availability of adequate energy resources can be met. Although the sun contributes 500 times the global energy input of all the other energy sources on earth, and its availability is assured for eons to come, to a large extent the applications of solar energy depend upon their economic feasibility because solar energy is not concentrated and large areas are required to convert it into useful forms. An appropriate balance will have to be struck among conflicting economic, environmental, and societal requirements. If feasible ways can be found to convert solar energy either directly into heat, power, and/or electricity, or indirectly, in the form of biomass (wood vegetation and organic solid waste), wind, hydropower, and temperature differences created in sunwarmed ocean waters, solar energy could supply a significant portion of future global energy demands. The major challenge to the application of solar energy on a global scale is that it is not a concentrated energy resource. It has a low supply density, which must serve societies with a broad range of demand densities. Therefore, current solar technology development is focusing on near-term applications such as water heating, passive heating of buildings, industrial process heat, biomass and wind conversion. The potential of small scale solar technologies appears to be sufficient to meet the energy demands of dispersed populations; however, the continuing migration of populations to urban centers and the needs of energy-intensive industries will make it difficult to meet projected energy demands with small scale solar technologies even if energy consumers are located in areas with exceptionally favorable climatic conditions. The overall energy requirements in Third World countries are vast, ranging from the needs of widely scattered villages to large urban centers. Most of the developing countries are embarked on massive industrialization programs from which they do not plan to turn back. But it is very optimistic to expect that small scale solar technologies alone would be able to meet even a low global energy demand. Therefore, it is imperative that the world community develop both small scale, decentral-
ized, and large-scale, centralized, solar technologies; not only rooftop panels, solar cookers, and windmills, but hydroelectric power, solar thermal conversion, photovoltaics, ocean thermal conversion and solar power satellites capable of generating power on a utility scale to meet social, environmental, and economic criteria. The political consequences of developing globally applicable solar energy technologies are likely to be far reaching, and worth an unprecedented effort in international cooperation. Such cooperation could lead to a safer and more stable world. In contrast, the use of energy resources based on nonrenewable fuels is more likely to have the opposite effect because the energy resources or the technology required to convert them into useful forms are under the political control of only a few nations. Therefore, the most desirable solar energy technologies will be those which meet the following criteria: significant global impacts, conservation of materials resources, economic competitiveness with conversion methods based on the use of nonrenewable energy sources, environmental benignancy, and acceptability to the countries of the world. POWER FROM SPACE FOR USE ON EARTH Third World countries, together with developed countries, should consider space — an ocean rich with energy materials and opportunities — as the new frontier containing resources critical to the long-term survival of humanity. Since the dawn of the technological era, the extension of human activities into space had been a challenge — one only recently overcome. The lunar landing in July 1969 and the successful mission of the space shuttle in April 1981 have shown that space and all its energy and materials resources are accessible. However, even with all the potential benefits to future generations on this planet, to most of the people in the Third World, many facing the immediate and mundane problems of their daily existence, space remains as remote and incomprehensible as the astrophysicists' discussions of “black holes.” Therefore, a major task will be to provide information to Third World decision makers that verifies space as being a new frontier for all the world's people. One option which could meet the suggested criteria for the development of solar energy technologies and which is particularly relevant to the Third World is the conversion of solar energy in space for use on earth. The proposal to convert solar energy to electricity in an orbit around the earth and then transmit the electricity via microwaves or laser beams to ground stations for distribution through a regular utility system was advanced in 1968. The solar power satellite (SPS) concept challenged the then prevalent view that solar energy conversion could not make a significant contribution on a global scale and indicated that there are no known limits to the amount of energy available in space. Although not a panacea for increasingly complex environmental and other societal problems of energy supply, the SPS concept represents an alternative direction for developing renewable energy sources, and for engaging in sustainable human activities in space in the 21st century. Energy delivered to the earth from space could overcome the physical, societal, and institutional limitations which future generations will be subjected to by dwindling energy resources on earth. The SPS concept could break open the closed terrestrial ecological system so that humanity need not be forced to live from generation to generation facing the threats of food and energy shortages and suffering the resulting social upheavals. Extraterrestrial resources could help meet the requirements of the global population in the 21st century. If these resources are not taken
advantage of, the peoples' insistent demand for improvements in living standards could be very difficult to meet. In the SPS concept which has been the basis for most current studies, solar cell arrays would convert solar energy directly into electricity and feed it to microwave generators forming part of a transmitting antenna. The antenna would precisely direct a microwave beam of very low power density to one or more receiving antennas at desired locations on earth. At the receiving antennas the microwave energy would be safely and efficiently converted into electricity and then transmitted to users. An SPS system could consist of many satellites located in geosynchronous orbits about 36,000 km away from the earth's equator so that each satellite would be stationary with respect to any desired longitude. The SPS concept has been given serious consideration in many countries, including Austria, England, France, Germany, Japan, the Soviet Union and the United States, and by United Nations bodies, particularly the Committee on the Peaceful Uses of Outer Space. The most extensive studies have been performed by the U.S. Department of Energy, which has evolved an SPS reference system. The satellite portion of this system would consist of solar cell arrays covering a 5 x 10 km area. A 1 km diameter transmitting antenna would direct the microwave beam to a 10 x 13 km receiving antenna on earth, where 5 million k W could be delivered nearly continuously. INTERNATIONAL IMPLICATIONS OF THE SPS As the benefits of the SPS system will extend beyond national frontiers, the development decision should not be left exclusively to national jurisdictions but be made part of transnational affairs. Developing countries should be given opportunities to participate. The SPS concept should advance the complementary national interests of both developed and developing countries because its benefits are global. In view of the extended time scale for the research to establish the overall feasibility of the SPS concept and for subsequent engineering development and verification phases culminating with a prototype SPS in about 20 years, followed by commercialization, it is unlikely that the impacts of the SPS will be felt by Third World countries for at least the next 40 years. A similar time scale will be required for terrestrial solar energy applications or any other alternative energy source which might have a significant impact on world energy supply. The SPS has the potential of revolutionizing the standard of living in developing countries, not only by directly providing a source of power for cities, transportation systems and industries, but indirectly, by powering chemical synthesis plants providing liquid fuels for dispersed populations. The latter would release billions of tons of dung and firewood for other uses and thus provide major ecological benefits to those parts of the world most severely threatened by increasing fuel shortages. The shift from nonrenewable to renewable fuels in the developed countries would stabilize the prices of nonrenewable fuels, thus making them more available to Third World countries. New policies will be required to guide decisions regarding the future course of SPS development from a global perspective. International agreements will require not only participation by all countries which could benefit from an operational SPS, but, more importantly, an appreciation of the opportunities and challenges which will face the introduction of a global SPS system. Institutions in developing countries, for example in India, have expressed serious interest in the SPS but much more infor-
mation will have to be made available on the economic, environmental and societal as well as technical issues. Typical reservations about the SPS, based on insufficient information, include the vulnerability of the SPS to sabotage, the impact of the microwave beam on the atmosphere, the effects of effluents from the SPS rocket launches and of the waste heat released to the atmosphere at the receiving antenna site. However, the U.S. Department of Energy assessment of the SPS concept and other studies indicated that no environmental constraints have been identified which would place undue constraints on the operation of the SPS. Land under receiving antennas at selected sites, even in desert regions, may be an important source of food if the design of the receiving antenna includes secondary uses, such as environmentally controlled agriculture. Offshore floating receiving antennas located near major population centers have the potential to produce fish protein through mariculture. Studies of the mariculture potential of receiving antenna structures indicate that one antenna site could supply 10% of the U.S. fish catch. The legal basis for the use of geosynchronous orbit also will require further definition. Already, some developing countries located near the equator have claimed sovereignty over geosynchronous orbit above their territory. The conflicts resulting from such claims could be reduced if an international agreement can be reached to assure that the SPS system would be operated and owned by an international organization operated for the benefit of humanity, perhaps modelled after the INTELSAT Corporation, which is owned by 105 countries. Third World countries view technology as a catalyst to help them achieve the aspirations of their peoples, and they look at the energy problem that they are facing in the context of social changes which will have a positive effect on their peoples' lifestyles. To achieve the desired effects, the appropriateness of either small scale decentralized (soft) solar technologies or large-scale centralized (hard) technologies should be considered. But there is a difference in the contributions of these technologies which clearly underlines the interrelationships between energy and social and economic factors. Unapplied technology is a neutral factor; but when a specific technology is applied, its contribution is closely related to social circumstances. Consequently, because the solutions of vexing energy problems vary for different countries, even for different regions of a single country and for urban and rural areas, proposed solutions may arouse great concern. Advocates of either "soft'' or “hard” technology solutions to energy problems tend to offer either one or the other as “the” solution, rather than choosing the technology most appropriate to solving a particular problem in a particular locale. Although it is likely that each country, whether developed or developing, will approach solutions to its energy problems in ways which will tend to optimize economic and societal objectives, a coherent global energy strategy based on a consensus of global development objectives and basic ground rules of humanity and equity should be considered. The time horizon for SPS implementation encompasses a period well beyond the turn of the century. The increasing role of the Third World on the international scene, the dynamic changes taking place in the scientific and technical fields and the hopes and aspirations of all people for a better life cannot be met without pursuing all worthwhile options for energy production. There is as yet no consensus in the scientific and technical community on the optimum solutions to complex energy supply problems. Thus it is not surprising that faced with the array of technology options, whether based on distributed or centralized technologies, there is a reluc-
tance to make large commitments until there is a clear understanding of the costs and benefits of specific technologies. However, there is an overriding need not to foreclose reasonable options until there is sufficient scientific evidence either for or against the specific technology to warrant its development or discontinuation. Although there may be disagreements about the specific technologies which should be developed, there should be no doubt that new knowledge, increased understanding, and enhanced scientific and technical capabilities will be essential to confront the challenges which must be met to assure that Third World economic development can proceed on a time scale which is meaningful for the societies involved. One of the primary problems in developing countries is that of unemployment. Therefore, each project must be considered in terms of its employment potential for the country: in India alone, for instance, approximately 35 million employable people are unemployed. Another concern is that developing countries will not be able to augment employment in the development and construction phases of a large project. However, labor in many of these countries is much cheaper than in developed countries, and, therefore, research and manufacturing projects can be undertaken economically within the framework of an international project such as the SPS. For example, during the implementation phase of the SPS there is a potential for the industrial production of photovoltaic and electrical components, and for receiving antenna construction in a specific country. Studies of the investment and employment potentials of the SPS and their effect on Third World countries should be conducted within the framework of an international organization which could be set up to manage and operate a global SPS system. It is axiomatic that when cost- competitive energy is available from renewable resources, economic development will be able to proceed with profound impact on employment because energy availability is a key determinant of economic growth in any country. CONCLUSION The global energy crisis mandates that all reasonable options to resolve it be kept open. One of these options, based on technologies already in general use, such as photovoltaics, microwaves and rocketry, is to harvest energy from outer space for delivery as base load power to meet urban, industrial, and other major energy needs. Environmental, societal, and political problems consonant with development of this renewable and fundamental source of energy indicate that research, demonstration, and the dissemination of information on solar power satellites should be conducted on an international basis. The benefits of energy from space are global, and the breadth of the concept provides ample opportunity for constructive participation by all nations in bringing its potential to reality. Therefore we recommend that the United Nations consider solar power satellites within the framework of initiatives undertaken to assure that the inexhaustible energy and material resources of outer space will contribute in increasing measure to benefit humanity. BIBLIOGRAPHY Books Clarke, Arthur C., The Promise of Space, New York, Harper & Row, 1968. Desai. B. G., Energy Policy for India, Vadodar, Bindoo Printing Press, 1978.
Grey, Jerry, Ed., Space Manufacturing Facilities, Volumes I, II, III & IV, Proceedings of the Princeton/ AIAA/ NASA Conferences of 1974, 1975, 1977, 1979 and 1981, New York, American Institute of Aeronautics and Astronautics, 1977-81. Grey, Jerry, Enterprise, New York, William Morrow and Company, Inc.. 1979. Haefele, W., Energy in a Finite World. Cambridge, Massachusetts, Ballinger Publishing Company. 1981. Levy, Lillian, Space: Its Impact on Man and Society, New York, The Curtis Publishing Company. 1965. Lyons, Stephen, Sun: A Handbook For The Solar Decade, San Francisco, Friends of the Earth, 1978. O'Neill, Gerard K., The High Frontier: Human Colonies in Space, New York, William Morrow and Company, Inc., 1977. Vajk, Peter J., Doomsday Has Been Cancelled, California, Peace Press, 1978. Reports An Outlook for India's Fugure (2000 A.D.). An Interim Report on Futurology — Energy. Department of Science and Technology, New Delhi, Sept. 1976. Solar Power Satellite Systems Definition, Conference on Energy and Aerospace, Prepared by Gordon Woodcock for the AIAARAS, London, Dec. 5-7, 1978. Some Questions and Answers About the Satellite Power System (SPS), DOE/NASA Satellite Power System Concept Development and Evaluation Program, U.S. Department of Energy, Washington, DC, Jan. 1980. Space Industrialization, An Overview, Final Report, Vol. L, Science Applications, Inc., Huntsville, Alabama, April 1978. The Role of Space Technology in the Developing Countries, presented by David Criswell, Peter Glaser, Rashmi Mayur. Brian O'Leary, Gerard O'Neill and Peter Vajk at NGO Forum on Science and Technology for Development, Vienna, Austria, Aug. 19-29, 1979. Grey, Jerry, “Tomorrow's Energy: Power from Inner and Outer Space,” Journal of the Power Division, ASCE, Vol. 104, No. POL Proc. Paper 13564, Feb. 1978, pp. 17-33. The Development of Solar Power Satellites, presented by Peter E. Glaser at the 1978 Annual Meeting. American Section of the International Solar Energy Society, Aug. 28-31. 1978. Denver, Colorado. Report of the Secretary General, United Nations Conference on New and Renewable Sources of Energy, Oct. 1979. Program Assessment Report Statement of Findings, Satellite Power Systems Concept Development and Evaluation Program, U.S. Department of Energy, Office of Energy Research, Solar Power Satellite Project Division, DOE/ER-0085, November 1980. A Bibliography for the Satellite Power System (SPS) Concept Development and Evaluation Program, U.S. Department of Energy, Office of Energy Research, Solar Power Satellite Project Division. DOE/ER-0085, April 1981. Solar Power Satellite: Systems and Issues, Office of Technology Assessment, Congress of the United States, August, 1981. Journal Space Solar Power Review, Vol. 1, Nos. 1 & 2, 3, 4, 1980, and Vol. 2, Nos. 1 & 2, 3, 4, 1981, New York, Pergamon Press. Articles Mayur, Rashmi, Solar Energy, Forum of Free Enterprise, Bombay, 1978. O'Neill, Gerard K., Space Colonies and Energy Supply to the Earth, Science 190, 943-947, 1975. Rangarao, B.V., Alternatives in Energy Development, Economic and Political Weekly, India, July 6, 1964, pp. 1063-1069. Glaser, Peter E., Power from the Sun: Its Future, Science 162, 857-886, 1968. Glaser, Peter E., The Solar Power Satellite—Past, Present, and Future, Space Solar Power Review 2, 13, 1981.
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0191 -9067/81 /040337-10$02.00/0 Copyright ® 1981 SUNSAT Energy Council ANALYSIS OF GEOSTATIONARY ORBITAL SLOT AVAILABILITY FOR THE SPS PROGRAMME RICHARD J. FLOWER British Aerospace Dynamics Group Bristol. England Abstract—Analyses were carried out. using predicted future geostationary satellite numbers and distributions, to examine geostationary orbital slot availability on a global and domestic basis. The various international considerations applicable to the geostationary orbit are discussed, with particular attention being paid to potential conflict areas. The factors involved in the definition of geostationary satellite spacing conditions are described, and their effects analysed with respect to SPS. Three separate distribution characteristics are considered to estimate geostationary satellite numbers and distributions in 1991. From these distributions, predictions are made of orbital slot availability as a function of satellite spacing on a global basis, and also when applied specifically to the U.S.A, and W. Europe. In the European case, attempts are made to compare regional consumption area power density demands with potential orbital slot availability for the SPS. INTRODUCTION The first successful geostationary communications satellite was SYNCOM 2 in 1963. Since then, numbers have increased rapidly with the global INTELSAT series, various domestic and international systems, and military and scientific satellites. The present total of active GEOSATs is estimated by the author as 73, with a predicted 273 further launches before 1991. It is thought that there will be 239 active satellites in geostationary orbit by the end of 1990 (1). Already the geostationary orbit has proved so popular that orbital overcrowding has become a potential problem. It is not so much that the satellites may collide with each other — although this does have to be considered — as it is a problem of electromagnetic interference. This problem will have to be very carefully analysed with respect to the massive projected demand of the SPS programme upon the geostationary orbit. INTERNATIONAL AND LEGAL ISSUES A number of existing international organisations, both scientific and political, are involved in the governing of space objects at geostationary heights. The public international institutions include the UN (and in particular COPUOUS), and the ITU. With respect to SPS, there are several issues in need of clarification before the
allocation of the necessary numbers of geostationary orbital slots can be formally approved at an international level. The accepted procedure for space exploration has always been the “first come, first served” principle, with the proviso that the exploration and use must be carried out for the benefits and in the interests of all countries, irrespective of their degree of economic or scientific development (1). It would seem that, using the interpretation that it is internationally beneficial in a general sense, the SPS programme would fulfill this condition. Formal confirmation of this will still have to be obtained, however. It is likely to be argued that the keeping of a GEOSAT in orbit for 30 years — the expected lifetime of an SPS — constitutes national appropriation, contrary to the 1967 Outer Space Treaty. This point will certainly need clarifying. Another potential problem area arises from the fact that there is no formal definition as to where sovereign airspace ends and outer space begins. This led to the 1976 Bogota Declaration, issued by 8 equatorial countries, claiming sovereignty over the segments of the geostationary orbit lying above their territories. This declaration has been rejected by the space resource countries and others, but again a formal ruling is required. The basic motivation behind the declaration was the belief that the space resource countries had monopolised the geostationary orbit. This is certainly a valid point in the light of talk about possible orbital overcrowding, before many developing countries have any satellites of their own. Because of limitations on the availability of the radio spectrum, an international organisation (the ITU) was set up to make allocations of radio frequencies to maximise the spectrum's efficient utilisation. It is still unclear whether the ITU has the power to deal with microwave frequency allocations — such power would automatically give it the right to allocate geostationary orbit positions for the SPS (1). Before any such procedures can be put into effect, however, thorough investigations are needed into the effects of the microwave beam on radio astronomy, shipbome radar, communications systems, and other services. The conflict of interests between present and potential users of the geostationary orbit, whether concerned with physical space, RF interference, shadowing, or some other effect such as collision risks, can only be resolved by international agreement. It remains to be seen whether the UN, the ITU, or a new international entity will be given the principle responsibility for protecting national and international wants and needs for the efficient, economic, and equitable use of the orbit. ORBITAL AVAILABILITY FACTORS The minimum separating distance required between geostationary satellites varies tremendously depending on the criteria used for arriving at an estimate. These criteria include the satellite size (and consequent shadowing and collision characteristics), the degree of tolerated electromagnetic interference, the stability of the orbit, the state of the technology, and many other factors. One estimate (2), has suggested that SPSs and other space objects may be obliged to maintain a separation of 2° from each other while in orbit above the equator — thus restricting the number of available slots to 180. Actually, since the geostationary orbit has considerable depth and width, and many present satellites are only a few metres in diameter, the orbit could physically
suggested (3), up to 5 satellites per degree of orbital space, giving a total of 1800. Thus, the question of orbital slot availability seems to have little to do with purely physical limitations. This does not necessarily apply to the immense dimensions of the SPS, however, as discussed below. RADIO FREQUENCY INTERFERENCE It is presently proposed that a 100 MHz bandwidth, centred on 2.45 GHz, will have to be reserved for the SPS system in order to protect other users from interference. In addition, if harmonics prove troublesome, other exclusive bands may have to be designated. The 100 MHz band should protect ground based communication links in adjacent bands— although this may not be justified in the case of communications satellites, as they will be much closer to the SPSs. One estimate (4) has postulated that a separation of 26° is needed between a Comsat and an SPS to avoid gain compression effects at the ground station, and 9° is needed to avoid similar effects at the Comsat. These estimates are subject to vast areas of uncertainty, but it is obvious that the above conditions are totally impractical and that much work is required in this direction. SPS harmonics could cause problems in various ways, and it is estimated that they must be suppressed at least 90 dB below the fundamental to avoid difficulties with most users. More stringent limits than this may be necessary to protect earth stations which receive signals from Comsats. It has been suggested (4) that at least a 3° separation may be needed to enable a Comsat-to-Earth link to be able to operate successfully at harmonics of the SPS fundamental frequency. Once again, uncertainties abound. The overriding message is the importance of the optimisation of the use of the radio spectrum. To this end, a number of design variables need to be investigated. These include — The degree of common frequency usage — The degree to which two satellites may illuminate the same area of the Earth's surface — Earth station antenna size and design — Antenna polarisation — Reversal of frequency assignments — Modulation type and degree — Interference allowances. All of these variables must be considered in all their combinations and variations in examining the concept of discrete orbital slots and the danger of spectrum/orbit scarcity (3). COLLISIONS Calculations carried out for 5 m diameter satellites indicated that 100 inactive satellites of such a size in geostationary orbit would produce less than one collision every 500 years. Thus, for active and passive satellites of this size, the danger of collision is negligible (3). However, a totally different picture emerges if we consider large space structures. A 5 GW SPS, for instance, could have a total area of arond 50 km2.
Calculations indicate that one complete 10 GW SPS in geostationary orbit would suffer approximately 10 collisions from 100 hypothetical inactive satellites above 3 m square during its 30-year operational lifetime (4). It is thought that this quoted figure of 100 inactive satellites in geostationary orbit could well be a realistic estimate in the light of planned missions and predicted launch rates. The current reference system SPS is sized at 5 GW, so the number of collisions would be significantly reduced. However, the reference system also assumes construction in geostationary orbit, which would involve additional collisions during the construction operations. There is a possibility, if the number of predicted collisions becomes too large, or if the collisions are likely to cause significant damage, that the orbit may need to be “cleared” of inactive satellites before implementation of the SPS programme. SHADOWING AND ECLIPSES At certain times of the year, all geostationary spacecraft pass through the Earth's shadow for short periods of time. Fortunately, these eclipses occur at local midnight when power demand is small, so the impact on supplies from an SPS will be at a minimum. Nevertheless, reserve capacity must be available. These eclipses occur during two 45-day periods each year centered around the equinoxes. The maximum time in shadow is 70-72 min, and this decreases rapidly on each side of the equinox. The overall effect, it is estimated, will be an annual reduction of less than 1% of the total power produced by the SPS. Eclipse conditions can also occur if a series of satellites are closely spaced in geostationary orbit. Calculations performed for the 10 GW SPS suggest that, for a 0.5° separation between neighbouring SPSs, mutual shadowing will occur twice per day over a total orbital angle of 12.48°. Each shadow period will last 25 min, with a depth of shadow varying between 0% and 77%. The total loss of power due to shadowing over any orbit is estimated at 1.2%. However, if the variation in the sun's latitude is taken into account, it becomes apparent that successive satellites can only be shadowed for 13 days per year. Consequently, the effect is very small indeed. GLOBAL SLOT AVAILABILITY As mentioned previously, the author has found evidence of 73 active geostationary satellites at the beginning of 1980, together with 103 documented planned missions (5). The functions and positions of these satellites, where known accurately, are summarised in Fig. 1. In order to gain information about the longitudinal distribution, the satellite numbers were related to 12 equal sections of 30° in the geostationary orbit. In addition to this, 170 additional launches were postulated for 1980-91, to bring total launch numbers for this period up to the figure mentioned in the Introduction. These 170 additional launches were longitudinally distributed in three different ways in order to yield a wider data base. The first case allows for an additional distribution
which is simply a duplication of the present/planned satellite distribution. The second case assumes that the additional satellites are spread evenly over the entire longitudinal range, and the third assumes an additional distribution which is the inverse of the present/planned satellite distribution — a sort of “filling in the gaps” scenario (6). The total 1991 predicted satellite numbers were then proportionally reduced to allow for satellites reaching the end of their life, and to lead us to the figures of 239 active geostationary satellites mentioned in the Introduction. The predicted number of empty orbital slots in 1991 was calculated for each 30° sector by simply subtracting the number of satellites in that sector from the total number of available slots (100 for 0.3° separation, 60 for 0.5° separation, etc.). Separate calculations were carried out for the three distribution cases, and also for four satellite separation conditions — 0.3°, 0.5°, 1° and 2°. The full results are presented in (6). One factor to be allowed for in the calculations is longitude-sharing of satellites — i.e., the use of the same basic longitudinal position, but with small orbital inclinations or eccentricities. Analysis reveals that 11 of the 73 present GEOSATs share longitude locations, and the surprisingly high total of 92 is reached if planned satellites are included. It is suggested that this latter figure is rather inflated due to the fact that many of the future satellites will simply be replacements for present versions, and will thus have the same position. In addition, many of these future satellites are several years distant, and some may well have their positions altered when consideration of other satellites in their vicinity (particularly foreign) is taken into account. A compromise figure of 25% was suggested for the proportion of satellites sharing longitude locations in 1991. This would reduce the total number of filled slots by 12*/2%, and the number of available slots for SPS would thus show a corresponding increase. This assumes a maximum of two satellites per orbital slot, which is not always the case, as up to five have been planned for some slots. Longitude-sharing would not be practical for SPSs, due to their complex nature and vast sizes. Complications are caused by increased collision possibilities, twice-daily eclipsing, and the need to continually readjust the microwave beam to allow for orbital eccentricities. In addition, the microwave beam would need to be turned off twice a day, when the sharing satellite appears in the firing line. Adding up the empty slot numbers for each of the 12 longitudinal sectors, and assuming a 25% longitude-sharing figure, the following figures were arrived at for the total numbers of global orbital slots potentially available for the SPS (6): 988-995 slots for 0.3° spacing 508-515 slots for 0.5° spacing 148-155 slots for 1° spacing (—32)—(—25) slots for 2° spacing. The negative numbers indicate that it is predicted that there will be more satellites than available slots for the 2° spacing condition. In these and all calculations, the geostationary satellite numbers have been assumed to stay at the predicted 1991 level for the duration of the SPS programme. Further orbital demands after this date have thus been assumed to be met by increased satellite capabilities, rather than increased numbers. U.S.A. SLOT AVAILABILITY It is predicted (7), that SPSs to serve the U.S.A, will need to be placed over
S. America (where the geostationary orbit passes over Ecuador, Peru, Columbia, and Brazil), and to the west over part of the Pacific. The longitudinal limits are approximately 225° and 315° E—yielding a total of about one-fourth of the geostationary orbit. Calculations were carried out as before, including only the longitudinal sectors falling wholly or partly within this range. The results were 237-250 slots for 0.3° spacing 117-130 slots for 0.5° spacing 27-40 slots for 1° spacing (- 18)—(—5) slots for 2° spacing. These results seem to indicate that 1° spacing is impractical for the 60 SPSs required in the reference system. A 0.5° spacing does seem to supply sufficient orbital slots to meet these requirements, however. Even this number could become critical if Central and S. American countries achieve significant orbital slot allowances, or demand sufficient SPS energy to necessitate large increases in SPS numbers within the relevant longitude range. W. EUROPEAN SLOT AVAILABILITY The complete longitudinal range for W. Europe is 336°-30° E, although the vast majority of the territory is situated between 350° and 25° E, with only Iceland further west and Greece further east. This claims a geostationary position of 35°, or 25,760 km of in-orbit distance. Possible reserves for W. Europe could be raised by longitudinal offsets over the Atlantic up to about 340° E. Eastern longitudinal offsets would not be practical due to probable conflicting claims from E. European, Africian, and some Middle East countries. In fact, such conflicting claims are likely over the whole longitude range considered here, with some 30 or so countries geographically involved. This will certainly generate complex political and legal problems associated with geostationary slot allocation. Using equivalent calculation methods as before, applied to the longitudinal sectors lying within the 340°-25° E range, the following results were yielded: 118-123 slots for 0.3° spacing 58-63 slots for 0.5° spacing 13-18 slots for 1° spacing (—9)—(—5) slots for 2° spacing. These figures are reduced by approximately 20% if the longitudinal-offset contributions from SPSs in the 340°-350° E range are discounted. Present W. European scenarios seem to quote 24 SPSs as the absolute minimum acceptable, with 70 as an upper limit (8). These figures do not include possible contributions from the 340°-350° E range. Examination of the above results reveals that orbital slots could well be at a premium, particularly when the complex legal and political situation is taken into account. As in the U.S. case, 1° spacing seems totally impractical. W. EUROPEAN ANALYSIS With the identification of specific major consumption sectors (8), a much more
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