SPACE SOLAR POWER REVIEW Volume 2, Numbers 1 & 2, 1981 SPECIAL ISSUE: TOULOUSE SOLAR POWER SATELLITE SYMPOSIUM
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 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—Telefun ken 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.
A Special Issue of Space Solar Power Review Proceedings of International Symposium on Solar Power Satellites Colloque International sur Les Satellites Collecteurs d’Energie Solaire Toulouse, France 25-27 June 1980 John W. Freeman Editor PERGAMON PRESS NEW YORK • OXFORD • TORONTO • SYDNEY • FRANKFURT • PARIS
Pergamon Press Offices: U.S.A. Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. U.K. Pergamon Press Ltd., Headington Hill Hall, Oxford 0X3 OBW, England CANADA Pergamon Press Canada Ltd., Suite 104, 150 Consumers Road, Willowdale, Ontario M2J 1P9, Canada AUSTRALIA Pergamon Press (Aust) Pty. Ltd., P.O. Box 544. Potts Point, NSW 2011, Australia FRANCE Pergamon Press SARL, 24 rue des Ecoles, 74240 Paris, Cedex 05. France FEDERAL REPUBLIC Pergamon Press GmbH, Hammerweg 6, Postfach 1305, OF GERMANY 6242 Kronberg/Taunus, Federal Republic of Germany Copyright ® 1981 Pergamon Press Ltd. Library of Congress Cataloging in Publication Data International Symposium on Solar Power Satellites (1980 : Toulouse, France) Proceedings of International Symposium on Solar Power Satellites = Colloque international sur les satellites collecteurs d’energie solaire. (Space solar power review. ISSN 0191-9067 ;v. 2, no. 1-2) English or French. Contents: The world and energy / Marc Pelegrin - The solar power satellite / Peter E. Glaser - Conclusions of the Huntsville SPS Conversion Workshop / J. R. Williams - [etc.] 1. Satellite solar power stations-Congresses. 1. Freeman, John W. II. Title. III. Series: Space solar power review ;v. 2,no. 1-2. TK1056.S66 vol.2.no. 1-2 621.31’244’0919s 81-2598 ISBN 0-08-027592-3 (pbk.) [621.31’244’0919] AACR2 Published as Volume 2, Numbers 1 and 2 of Space Solar Power Review and supplied to subscribers as part of their subscriptions. Also available to nonsubscribers. All rights reserved. No part of this publication may he reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical photocopying, recording or otherwise without permission in writing from the publishers.
SPACE SOLAR POWER REVIEW VOLUME 2, NUMBERS 1 & 2 1981 CONTENTS Special Issue: Proceedings of International Symposium on Solar Power Satellites Dr. Aigrain I Editorials Peter E. Glaser Marc Pelegrin 5 The World and Energy Peter E. Glaser 13 The Solar Power Satellite — Past, Present, and Future J. R. Williams 29 Conclusions of the Huntsville SPS Energy Conversion Workshop Dietrich E. Koelle 33 SPS Transportation Requirements — Economical and Technical J. Rath 43 Assessment of SPS Photovoltaic Solar Array Requirements I. V. Franklin 53 Some Critical Aspects of Solar Power Satellite Technology Klaus P. Heiss 61 SPS: An Economic Outlook Leo Thourel 71 Use of Solar Power Satellites: Evaluation of the Risks on Health and Environment D. J. Kozakoff 73 Solar Power Satellite (SPS) Antenna Measurement J. M. Schuchardt Considerations J. W. Dees Lewis M. Duncan 87 SPS Environmental Effects on the Upper Atmosphere I. R. Lindsay 103 Microwave Radiation: Biological Effects and Exposure Standards John M. Logsdon 109 International Dimensions of Solar Power Satellites: Collaboration or Competition? (Continued on next page) ISBN 0-08-025792-3 ISSN 0191-9067 (611)
SPACE SOLAR POWER REVIEW, Vol. 2, Nos. 1 & 2, 1981 (Contents continued) A. Orszag 115 Lasers et Transmission d’Energie Rashmi Mayur 127 Third World Views on Solar Power Satellite Applications Bertrand H. Chatel 135 Les Satellites Collecteurs d'Energie Solaire (SPS) et la Communaute Internationale I. H. PH. Diedericks- 143 Remarks on Some Legal Aspects of Solar Satellites Verschoor —An Overview R. V. Gelsthorpe 151 Some Aspects of Antenna Technology for B. Claydon European SPS A. W. Rudge Paul F. Combes 155 The SPS Transmitting Antenna Radiation Pattern Frederick A. Koomanoff 163 Satellite Power System Concept Development and Evaluation Program K. K. Reinhartz 169 Potential Interest in Europe in an SPS Development Maurice Claverie 179 Les Centrales Solaires Spatiales dans Ie Contexte Alain Dupas Energetique Mondial des Cinquantes Prochaines Annees Bjorn M. Kaupang 191 Integration of SPS with Utility System Networks Marc Pelegrin 197 Synthesis of the Final SPS Panel
0191 -9067/81/010001 -03$02.00/0 Copyright 1 1981 SUNSAT Energy Council EDITORIALS At the close of a decade that brought the long-term perspective of a shortage of fossil energy supply to the foreground, a worldwide effort has been launched in the fields of research and development to enable man to master technologies that will permit him to employ renewable energy forms based directly or indirectly on the energy generated by the sun’s influence on our environment. Among these new energy forms can be cited wind energy, the various types of sea energy, and, of course, solar energy. Numerous projects are under study. Yet, in the end, their utilization will depend on technological discoveries which will constitute the basis of their success on the economic level. The largest possible range of choice should be available so as to provide a satisfactory solution to a problem of such enormous influence on the future of our civilization. In this respect, the idea of solar power satellites — theme of the symposium organized in 1979 by the CERT in Toulouse, France — may be ambitious, in view of the sheer scale of the realization and exploitation problems it raises. The CERT symposium deserves credit for its contribution to taking an inventory of these problems. There is still much research to be done before, in the near future, man comes up with an answer to the question posed: can we envisage exploiting solar energy through the use of geostationary satellites? Whatever the answer may be, the vast amount of reflection and development it will require will inescapably bring about a beneficial innovation in numerous fields of activity, among which could be cited ground level recuperation of solar energy as well as space activities as a whole. Dr. Aigrain Secretaire d’Etat aupres du Premier Ministre Charge de la Recherche Paris, France The genesis for the International Symposium on Solar Power Satellites was a discussion with Dr. Marc Pelegrin, Director of the Centre D’Etudes et de Recherches de Toulouse (CERT) in the Spring of 1978, on the status of the Solar Power Satellite (SPS) concept. The SPS is based on the conversion of solar energy in space for use on Earth to generate baseload power; and it is gaining increasing international interest as a potential major option for meeting future global energy demands. The impetus for serious consideration of the SPS concept by the scientific and technical community was the SPS Concept Development and Evaluation Program being undertaken by the
US Department of Energy in cooperation with NASA and other US Government agencies. But now, the international implications of the development and deployment of the SPS are being studied in several European countries and by international organizations such as the European Space Agency and the United Nations Committee on Peaceful Uses of Outer Space. As a result, one of the technical approaches for the SPS concept as embodied in the SPS Reference System has been evolved by NASA to provide a basis for studies of the technical, economic, environmental, and societal issues by academic, industrial, and governmental organizations. By 1979, these studies had indicated that the SPS concept appears to be technically feasible and thus warrants further evolutionary development. Sufficient information was being developed so that several of the issues facing this evolution could be clarified and form a basis for policy decisions on future commitments to an SPS program. In view of the progress being made in SPS-related studies, an exchange of information at an international symposium devoted to the exploration of the issues surrounding the development of the SPS concept was considered timely. International participation is justified on the basis of the projected global application of the SPS concept as a source of continuous power available to all countries. The SPS will require the cooperation of the international community in an SPS program to assure adherence to agreed-upon environmental standards, to obtain allocation of appropriate frequencies and positions in geosynchronous orbit, and to evolve a legal framework consistent with its peaceful and global benefits. International participation in the development of the SPS would enhance the potential benefits, contribute to the improvement of international relations, and present an option in the context of global energy-related political, legal, environmental, and societal concerns. The organization of the symposium was undertaken by an international scientific committee presided over by Dr. M. Pelegrin and included Mr. M. Claverie, Deputy Director Solar Energy Programs, P1RDES, France; Mr. I. Franklin, Senior Project Manager, British Aerospace Dynamics Group; Dr. P. E. Glaser, President, SUNSAT Energy Council, USA; Dr. J. Grey, Director of Public Policy, Institute of Aeronautics and Astronautics, USA; Dr. R. Tilgner, Executive Secretary, Long Term Planning Group, European Space Agency, France; and Dr. R. Mayur, Member, Futurology Commission, Government of India. This committee undertook the task of preparing the program, inviting participants and attending to the many details. It was aided by a local organizing committee which, in addition to Dr. Pelegrin, consisted of Mr. J. Coulom, Administrative and Financial Counsel of the Office Nationale d’Etudies et de Recherches Aerospatiales and the staff of CERT. The symposium was sponsored by Mr. Andre Giraud, Minister of Industry, France, with the cooperation of the SUNSAT Energy Council, Commissariat a L’Energy Solaire, Direction de Recherches, Etudes et Techniques and Centre National Etudes Spatiales. The success of the international symposium can be judged by the contributions published in this volume, which indicate the broad-ranging interests of the authors. The 120 symposium attendees, representing both developed and developing countries, verified the need for international participation and demonstrated the level of international interest in the SPS concept and its future potential. The attendees expectations are that an international organization could best manage the development and subsequent commercialization of the SPS in a manner that would be responsive to the energy needs of individual countries and be politically feasible, cost-effective, conducive to international cooperation, and acceptable to
both developed and developing countries. This implies a broadening of the understanding of the challenges and opportunities of the SPS concept. These need to be explored by the scientific and technical community at meetings such as the international symposium in Toulouse and at meetings of international organizations such as the United Nations and the International Astronautical Federation. Such meetings will ensure that information will become available to the international decision makers. Perhaps the most cogent reason for consideration of the SPS at an international symposium is its potential, not only for baseload power generation on a global scale, but also for expanding human activities in space as the ultimate destiny of humanity. Peter E. Glaser Arthur D. Little, Inc. Cambridge, Massachusetts
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0191 -9067/81 /010005-08$02.00/0 Copyright ® 1981 SUNSAT Energy Council THE WORLD AND ENERGY MARC PELEGRIN Office National d'Etudes et de Recherches Aerospatiales Centre d’Etudes et de Recherches de Toulouse B.P. 4025, 31055 Toulouse Cedex France Does reality exist outside the human brain’s conception of it? A question without an answer, and one that will remain unanswered. Philosophers, as well as mathematicians and physicists, are divided over the thoughts this question evokes in their minds. As for me, a simple engineer, although daily confronted with concrete problems, I would be tempted to say that whoever claims to answer this question is putting forward a postulate that, like all postulates, is unwarranted and unverifiable: man, in his environment, has only models that he himself has created; he can marvel at the excellent performance of these models and consequently use them to predict the evolution of this environment, that is, to a certain measure, the evolution of the world. The recent conquest of space, however, has just pushed back the doubt between reality (what is the meaning of this word?) and the model practically universally accepted by mankind: putting a man on the moon and bringing him back confirms man’s theory of his own environment. It is a sublime confirmation of Newton’s theory and more simply, off = my. Yet the navigation of the great migratory birds, more than this astounding success, forces even farther back the limits of doubt between the model and “reality.” Man’s model is very close, let us say it is tangent, to that of the carrier pigeon or the stork: the proof of this lies in the results of experiments conducted in a planetarium where all celestial configurations, including the one we know, were possible: the migrants fashioned themselves a celestial pattern analogous to our own. In fact, I should say that man’s reconstruction of migratory bird patterns indicates that they use a celestial pattern analogous to his own. This long digression, which I hope you will excuse, shows that one's reality is another’s fiction and vice versa. Therefore, may those who still consider the theme on which our three-day discussions will be based, a fiction, rest assured: this is indeed the place for them; the subject is well worth the trouble. For the philosopher, the energy crisis is an unimportant economic incident. For the economist, it is a harsh reality he was unable to foresee although everything indicated the inevitability of such a crisis . . . But, I must admit, this is very easy to say — after the fact. The evolution of the price of consumer goods and services rendered by industrialized countries and the price of a ton of oil purchased from the Middle East showed such a divergence between 1965 and 1973 that this catastrophe was imminent: in constant francs, a ton of oil delivered to Europe in June 1970 cost 65 francs and in 1973: 306 francs!
I am not afraid to say that this inevitable crisis has been healthy: it has given the world a few decades warning of the physical shortages to come. It was only in 1975 that the reality and irreversability of this situation came clearly to light. Each country reacted differently (see Fig. 1). In the United States, President Nixon launched the Independence Plan whose objective was energy independence by 1980. This plan, many times revised, is very far from its fixed objective. In Europe, and particularly in France, the nuclear energy program has been reinforced and relatively little delayed in spite of very strong pressure by ecologists. Japan, though very poor in fossil resources, has fewer problems than other countries because of its surplus trade balance, nevertheless she is also banking on electronuclear energy. In short, all national economies, including those of the oil producing countries, have been deeply disrupted and a new world stability is still far out of reach. Everywhere, new forms of energy are being intensely studied, but there are many problems — particularly in the field of energy storage; on the whole, these new forms of energy just cannot compensate for the expense or scarcity of oil during the next two decades. After that period, I would put myself among those who believe the energy crisis will no longer exist; it is my opinion that fast-breeder techniques will be mastered industrially as will the problem of reprocessing irradiated combustibles. The fusion of deteurium-tritium-helium will perhaps be on the point of realization in the laboratory and, after one or two decades, we can hope to go on to the industrial stage. However, even in the light of these rather optimistic hypotheses, we must not fall
back on our present error by basing the activity of tomorrow’s world on only one energy source, even though it be twofold (uranium and seawater). The precise theme of this symposium is to explore the feasibility of a solar energy source capable of replacing the largest nuclear power plants presently projected for construction: 5 to 10 GW. During a recent symposium on innovation, I was led to define the term as follows: “Innovation normally consists of deliberate, daily technical progress, sought after and not undergone; in exceptional instances, it is the putting into practice of a new idea or invention. And I would add that to innovate is to desire to surpass routine, to progress, to refuse to remain passive when faced with the evolution of new techniques, but it is also to be conscious of the risks one runs in venturing off the beaten track.” A geostationary satellite system project that aims at collecting solar energy, transforming it, sending it to earth where it will be received, transformed a second time, and connected to energy distribution networks, constitutes a clear and precise example of innovation as defined above. Is it not the search for technical progress — deliberate, not undeigone, far from the beaten track? In spite of its ten year existence, the fundamental idea is so new that it will take another decade before the final problem of the project’s feasibility can actually be tackled. For the moment, all ideas relating to the overall system or the multitude of subsystems that will compose it must be greeted with humility, then analyzed without destructive apnorism. This symposium is the first to take place outside the United States and the first to be specifically dedicated to the solar power satellite project. More jostled than other continents by the energy crisis, less accustomed to innovative risks than the United States, aged Europe — perhaps wiser and more steadfast in its lifestyle — can make an important contribution to the project’s exploratory phase. This is one of the reasons for situating the symposium in a European city whose space and aeronautical vocation make her worthy of such a reception. The objectives of the symposium, consecrated to the feasibility of this gigantic innovation, are derived.from the analysis of the traditional and “new” sources of energy that our planet conceals. Even if one concedes that the present crisis is immediate rattier than long-term, there still remains a critical passage of two or three decades. What are the prospects? SHORT AND MIDDLE TERM PROSPECTS These essentially vary according to the country. Geothermal science is an interesting possibility, previously exploited yet still rich in promise, although the decrease in temperature of the presently exploited sinkings’ outflow (2 to 3 °C in ten years) is already somewhat disturbing. We can hope to reach a stabilized temperature — but at what level? For, at the scale on which we operate when an outflow exists, the temperatures are still difficult to estimate (“a transitory state” between the static temperature — at zero outflow — and the balanced temperature of the well’s nominal outflow can last more than a decade). In this case, human wisdom must dominate the search for immediate competitivity with other energy sources . . . still too inexpensive to avoid drying up the geothermal layers. As far as is absolutely possible, the sinkings should only be exploited at a stabilized temperature outflow. The reinjection process, mandatory in some countries, also
leads to the "conservation of resources,” even though this doubles the sinking cost and substantiality increases operating costs (pumps). We may note that this energy — rarely used except in heating as this relatively salt-charged water rarely exceeds a temperature of 80 to 100 °C — is not of solar origin, in the common sense of the word; like coal or oil, it comes from the earth’s crust but the two former substances constitute potential energy (a chemical reaction is necessary to extract energy from them), while an operating geothermal layer brings energy directly to the earth’s surface. We can also remark that geothermal deposits exist just about everywhere, in varying degrees, and are relatively well distributed in zones of human activity. Wind energy seems quite appealing at first glance (the maximum usable power is shown by the relation W = 0.38S-V3; W in kW, S in m2, V in m/s). For winds of approximately 15 m/s, a windmill equipped with good vanes (estimated output per vane: 60%) produces as much power per square meter as thermal collectors (estimated output 15% to 20%) in a country near the 45th parallel. But, as is often the case in the study of new forms of energy, these figures are deceiving as, 1 may add, are all averages. Figure 2 shows that, for countries situated between the
43rd and 46th parallel, the average annual energies due to sun and wind, expressed in identical units, are of roughly similar magnitudes. But what really counts is the consistency of furnished energy. The Rhone Valley’s average annual energy can scarcely be utilized because it is the product of a turbulent, capricious wind that blows approximately 100 to 120 days per year, and dies down at night. (This is only a disadvantage to the extent that the wind blows stronger during the day, exceeding the maximum productivity level of the vanes. In France, only Brittany’s coastal area (with winds of relatively constant force and direction) could be exploited. Generally speaking, the most important element is not the average annual energy provided but the distribution curve of exploitable energies superior to a given threshold, for 10- 20-30 hours etc . . . without interruption. One must not forget that the problems of high-scale energy stocking have not yet been solved. The most important stocks near a total of a few hundred MW-h on the daily level and some GW-h on the weekly grade. For the present, various other problems restrict the immediate interest of such resources: investment and maintenance costs, resistance to the outbreak of storms — be they only once every five or six years — noise, wakes far downhill from the windmill (between 10 and 50 “diameters”) and the unsightliness of the machine itself. This form of energy is directly linked to solar energy and to the rotation of the Earth. Energy taken from the sea takes three forms: (a) Tidal Energy There exists only one world site in operation: the tidal power station of Rance, in France, with a capacity of 240 MW, put into service in 1966. Our globe offers about ten potential sites (with tides greater than 10 m and dyke construction possibilities). This is consequently not an abundant and well-distributed energy source!* On the other hand, the modulation consistency is perfectly predictable. This energy is not of solar origin, but originates from an initial state (planetary movement) which, in fact, results from a slowing down of planetary movement (Earth-Moon) owing to energy dissipation in an oscillating system, unmeasurable even over a century, in its present state of operation. (b) Wave Energy Although several projects, notably Japanese, have led to experimental realization, this energy, not yet in use, does not seem likely to provide a solution to the energy crisis. Its linear density is low (one must consider the wave’s’space and time intervals and be aware that this is the work of “gravity”) and the energy collecting installations needed are gigantic structures. Yet, the heterogeneous material structures may end up making this type of energy more significant. The above energy is of solar origin. (c) Thermic Ocean Energy This is the process of exploiting the difference of temperature between surface *Among the possible sites: Chansey, France: 12 GW, Funday Bay, Canada: 5 GW, A. San Bay, Korea: 2 GW; the remaining sites (Arctic Ocean, India, Australia) hardly account for more than 20 GW.
waters (25 to 28 °C) in tropical zones, and those of the ocean floor (6 to 8 °C) at depths to the order of 600 m off Abidjan, Ivory Coast, by means of a conventional thermal machine, complemented by an adapted working fluid. The only explanation for the low temperature of the seabeds is their reception of permanent supplies from polar waters. George Claude made an endeavour to capture this energy during the 1930’s at Abidjan, but a storm destroyed the installations while still in construction. Various projects are actually being carried out, some of which correspond to realsized installations (several hundred MW-h) on floating platforms. The platforms may well solve the problem of piping the pumped cold waters (which will then be vertical), but they do not provide a solution to the problem of transporting the energy produced. One project aims at producing hydrogen on the spot, to later transport it, in liquid form, to the mainland, by barge. This is solar origin energy. Biomass is undeniably an interesting energy source. But burning wood in a chimney will quickly become an expensive luxury, then a crime, for wood deserves a better end! Biomass potential energy density by m2 is and will remain low; added to conversion problems (organic matter) into CO or CH4 gas or methyl or ethyl alcohol, there is also fundamentally a collection problem, especially as concerns “forest residue,” that is, the substance that grows under a forest hindering its growth — a substance which would therefore be in our interest to collect. A “ripe” forest has reserves totaling 1700 MKj/ha, and an annual growth rate of 11 MKj/ha. This is clearly less than the quantity of energy provided by one hectare of cereals (35 MKj/ha) but biomass’ annual upkeep demands substantially less energy and labour. Energy resulting from biomass is part of the “planting and sowing, growth, harvest, collection and transformation” system and this is the perspective in which actual studies are being developed. Stocking problems are minor. The overall output is in the region of 1% to 3%. This energy is of natural solar origin, (distributed) which, if well exploited, can contribute to maintaining the present biological balance. What remains is direct solar energy, to be exploited either by thermal conversion on the blackest possible body or by photoelectric conversion. On Earth, this energy is modulated according to predictable variations (day/night, seasons) or unpredictable ones (cloud covering). Productivity in both cases, reported during bright periods, reaches approximately 10%. Thanks to the fall out of space problems it is probable that electrical conversion will claim recognition before the year 2000, even for heating facilities. Collecting solar energy in space can provide us with constantly available energy (except for a few hours, by satellite per year). Nevertheless, a certain number of problems remain to be solved. The theme of this symposium is therefore to make a contribution to the following question: Is the production of solar energy by means of geostationary satellites feasible? An answer should be given by 1990. Only then, if the answer is positive, will the real technical problems arise. However, it is not excluded to consider these problems even now, for they promise to be both difficult and numerous: in-space construction of the satellite itself, active control of the structure (it can hardly be conceived as infinitely rigid), energy conversion on board, its transmission, reception on Earth, and link-up with distribution networks. Security problems in case of beam deviation do not seem to present great difficulties, however a few hours annual eclipse is inevitable. Meanwhile, let us take note of the following problems:
Environmental: The presently accepted maximum power densities are inferior or equal to 10 W/cm2. It will be difficult to use denser beams. What influence will a permanent beam of this sort have on the different layers of the atmosphere and ionosphere? If other means are employed (lasers, particle beams) what effects will they have on the near-earth environment? Not originally destined for Earth, this energy becomes stricto sensus a kind of pollution. One may assume, however, that if it is not supplied in this way, an equivalent energy source will be extracted from terrestrial resources. Economic: From now on, this is a world issue — one that must consequently
adapt itself to both liberal and planned economies. How will we find the means, on an international basis, to manage these energy generators, each of which will correspond to several present-day nuclear power plants? How are we to distribute the energy? How will we adapt it to demand? Philosophical: What are the "reasonable” limits to the present generation’s right to withdraw resources from the earth (fossil and nuclear) and from the sun? To sum up this introduction to the subject that will take up your attention for the next three days, I wish to remind you of two numbers that should remain constantly present in our minds: (a) The upper atmosphere CO2 content increases regularly and rapidly (Fig. 3). The facts that attribute the increase to human activity are based on the slackening off noted on the curve between 1940-1945. A hasty conclusion, perhaps, but one that in no way dispenses us from following this evolution and measuring its results. A very brief examination shows that the "glasshouse effect” provoked by CO2 tends to become greater and, as a result, so does the average earth temperature; but this factor would be offset, at least partially, by the greater amount of dust in the upper atmosphere: this would increase the atmosphere’s albedo thereby decreasing the quantity of solar energy to arrive on Earth. (b) The energy man presently controls has reached a level that can no longer be considered negligible with respect to the planet’s ecology: this portion is between 10 4 and 10 5 of the solar energy received on Earth. Most of this energy is of fossil origin; the portion that is of nuclear origin will inescapably increase during the coming years. Now, a magnitude that reaches a scale of 104 and 10-5 of the magnitude in question is no longer a “background noise.” The consequences of this supplementary energy supply from the earth’s depths, apart from the natural geothermal flux which is too weak in comparison with the other energies involved, can modify the planet’s biological equilibrium (along what exact lines, 1 do not know!) all the more so as these supplies are extremely localized. To finish nonetheless on a reassuring note, I wish to underline the fact that the Earth, ever since its creation 4 or 5 billion years ago has never been stabilized; its equilibrium, if this word has any real meaning, is a dynamic one, and whatever puristical ecologists may think, the deliberate stabilizing of the Earth in its actual state is also a form of pollution.
0191-9067/81/010013-16$02.00/0 Copyright ® 1981 SUNSAT Energy Council THE SOLAR POWER SATELLITE — PAST, PRESENT, AND FUTURE PETER E. GLASER Arthur D. Little, Inc. Cambridge, MA 02140 Abstract — The potential of solar energy is surveyed and the consequences of increased solar energy use are outlined. The connection is made between advances in space technology and efforts to harness solar energy and the objectives of the solar power satellite (SPS) concept are introduced. The technical challenges facing the evolution of the SPS are discussed in terms of solar energy conversion in orbit, power transmission to and rectification at a receiving antenna on Earth, transportation of payloads and orbital assembly and maintenance. The economic feasibility and the envirionmental and societal issues are highlighted and ongoing assessments of the SPS are mentioned. The international implications of the SPS are underlined and the common interests of both developed and developing countries recognized. The implementation of an SPS is presented as providing an impetus to achieving the inevitable transition to renewable sources of energy. THE POTENTIAL OF SOLAR ENERGY “It may be that, in the future, man will have no use for energy and be indifferent to stars except as spectacles, but if (and this seems more probable) energy is still needed, the stars cannot be allowed to continue in their old way, but will be turned into efficient heat engines” (1). This statement rings even more true today, now that we have rediscovered the inexhaustible potential of solar energy. The potential of solar energy as a source of power has been recognized and evaluated for more than 100 years. Efforts to harness solar energy accelerated during the last half of the 19th and the beginning of the 20th Centuries as the world’s energy needs grew as a result of the Industrial Revolution. These efforts subsided with the successful development of energy economies based, at first, on coal and, subsequently, on the use of liquid petroleum fuels. But then, in the 1960’s, the world’s fossil fuel resources were calculated to be finite and their availability only an ephemeral event — on the time scale of recent human history — of, perhaps, a few centuries (2). Subsequently, projection of energy consumption in the United States indicated that soon after the year 2000 a gap would be created which could be filled by solar energy (3) . There were growing concerns about the environment, about the role of nuclear power and, ultimately, about the possible large-scale use of coal as a long-term replacement for liquid petroleum fuels. These concerns and uncertainties were further compounded by the limits-to-growth philosophy and its implications, in the face of burgeoning populations and diminishing resources, on the maintenance of
living standards. And finally in this setting, culminating in the dramatic events of October 1973, the potential of solar energy was rediscovered and the development of solar energy technology was again being seriously pursued. Currently, solar energy research and development is directed toward new and improved technology, approaches to reduce the cost of conversion, and designs and processes to permit low-cost mass production. Although expectation for significant benefits are high, results on the desired scale are unlikely to be achieved quickly, not because of the lack of appropriate technology but because of the lack of appreciation heretofore of the potential of solar energy and therefore the limited experience with . such technology. Numerous studies project what will happen by the year 2000 and how to deal with global, national, and regional energy problems. Mostly, these studies focus on pricing, management, and allocation of available resources that must be dealt with within an existing infrastructure. However, changes which could be made within the existing infrastructure will not have an impact in the short term. But, they will have to be made to bring about the transition from oil and gas, and other nonrenewable energy resources, to the renewable energy sources which will be essential to the proper functioning of the energy economies in the future. Therefore, because the impacts of solar energy will not be widespread for one or two decades, the time horizon must encompass a period beyond 2000. Shifting too soon, or too quickly, to solar energy could strain national economies. Shifting too late, or too slowly, might also impose inescapable pressures on some fossil fuels, resulting in sharply escalating prices and consequent damage to these economies — as it happened in 1973 and continues to this day. Huge energy supplies will also have to become available if the developing countries are to approach the economic level of industrialized countries. The future annual energy resource requirements of developing countries are projected to be more than four times the total world energy production in 1970 (about seven billion tons of coal equivalents). As industrial countries will remain major users of the world’s energy resources, the prospect of supplying about 30 billion tons of coal equivalents per year (with the resulting environmental effects) to meet the aspirations of developing countries confirms the desirability, if not necessity, of a significant global use of solar energy. The political consequences of increasing solar energy use are likely to be the most far reaching and may require extensive and unprecedented international cooperation. But such cooperation could lead to a safer and more stable world. In contrast, the use of other energy resources based on nonrenewable fuels would be unlikely to have such desirable effects since most of these fuels are under the political control of only a few geographically favored nations. Solar energy could supply a major portion of future energy needs if effective ways can be found to economically and efficiently convert it to heat, power, electricity, or other fuels. Industry and government in many nations are investigating which solar energy applications are most likely to be successful, what products should be developed, how big the solar energy market will be, and when the potential of solar energy will be realized on a significant scale. The major challenge to the effective applications of solar energy is that it is a diffuse and distributed resource requiring large areas for conversion into useful form and, therefore, capital-intensive technology. The successful and widespread introduction of solar energy technology will require considerable development to strike the appropriate balance among the conflicting economic, environmental, and societal considerations.
THE SPACE TECHNOLOGY CONNECTION The launching of Sputnik on October 4, 1975, and the subsequent dramatic space pioneering efforts marked the entry into the Space Age which irrevocably changed the evolutionary direction of planet Earth’s civilization. The consciousness of the uniqueness of planet Earth and the tangible demonstration that the tools of the Space Age promise an unlimited extension of new knowledge of the solar system had a most profound influence on advances in technology. These advances not only made it possible to develop satellites for Earth’s observations and communications as well as for scientific purposes, but also significantly contributed to the development of electronics and computer technologies. The historic “one small step for man, one giant leap for mankind," taken in July, 1969, was a spectacular event which an estimated 500 million people throughout the world followed with rapt attention. This dramatic event has very practical long-range connotations. Just as the railroad in the 19th Century opened up frontiers for human settlement, so space transportation sets the stage for the movement of humanity beyond the Earth’s surface. The railroad was a technological solution to social problems — unsatisfactory social conditions that were caused by resource limitations were alleviated when the railroad facilitated the exchange of the agricultural products and natural resources of rural settlements for the manufactured goods of crowded cities. Similarly, space transportation can bring within reach of Earth’s civilization the solar system's immense resources — including the harnessing of solar energy on an unprecedented scale. The synergism between space technology and efforts to harness solar energy could be used to overcome terrestrial obstacles to the conversion of solar energy such as inclement weather and the diurnal cycle. If satellites can be used for communications and for Earth observations, then it is also logical to consider placing satellites that could convert solar energy in an orbit, e.g., geosynchronous orbit (GEO), where they could generate power for Earth continuously during most of the year. With a year-round conversion capability such satellites could be used to overcome not only the major obstacles to solar base-load power generation on Earth (i.e., its requirements for energy storage and its inefficient use of capital-intensive solar energy conversion devices), but to develop the technology for solar energy conversion in Space on a scale which may not be possible on Earth, by taking advantage of the zero gravity of Space and the absence of other terrestrial constraints on the erection of a lightweight, extensive contiguous structure. The way to harness solar energy effectively would be to move the solar energy conversion devices off the surface of the Earth and place them in orbit where they would be continuously exposed to the Sun and away from the Earth’s active environment. Obviously, the most favorable orbit for solar energy conversion would be around the Sun, but at this stage of space technology development GEO is a reasonable compromise because solar radiation in GEO — unlike solar radiation received on Earth — is available around the clock during most of the year. Solar radiation intercepted by a satellite in GEO will be interrupted by the Earth’s eclipses of the Sun from 22 days before to 22 days after equinoxes for a maximum period of 72 minutes a day when the Earth, as seen from a GEO position, is near local midnight. Overall, eclipses will reduce the solar energy received in an orbital position in GEO by only about 1% of the total available during a whole year. A solar energy conversion system in GEO will collect at least four times the solar energy that would be available to it on Earth, even in favorable geographical locations, because it would not be subject to interruptions by weather, atmospheric absorption, and the diurnal cycle.
THE SPS CONCEPT The Objectives In the 1960’s, the logical soundness of using the synergism of solar energy conversion technology and space technology led to the concept of the solar power satellite (SPS) (4). The SPS would convert solar energy into electricity and feed it to microwave generators forming part of a planar, phased-array transmitting antenna. The antenna would precisely direct a microwave beam of very low power to one or more receiving antennas at desired locations on Earth. At the receiving antennas, the microwave energy would be safely and efficiently reconverted to electricity and then transmitted to users. An SPS system would comprise a number of satellites in GEO, each beaming power to one or more receiving antennas. At the outset, the following objectives were proposed for the development of the SPS concept: • To be of global benefit; • To conserve scarce resources; • To be economically competitive with alternative power-generation methods; • To be environmentally benign; • To be acceptable to the nations of the world. The SPS concept challenged the view prevalent in the 1960’s that solar energy conversion methods could not make a significant contribution to energy economies, and demonstrated that there are no a priori limits to the development of energy resources in Space. Although not a panacea for the increasingly complex energy supply, environmental and societal problems, the SPS concept could open up a new evolutionary direction for human development of energy resources. Today, we have shed our illusions that we have unlimited capabilities to control and fashion our environment, and we no longer hold a naive belief in the unlimited bounty of nature. Nor can we continue to treat natural resources as a rightful inheritance which we are free to mine, burn, exploit, and waste on our immediate needs with scant regard for their irreplaceability. If we consider the Earth a closed ecological system in which humanity is destined to live from generation to generation, then the limits to growth conjure up famines, shortages, and social upheavals. This view of a future apocalypse would have to be considered a possibility and we would have to do the best we can to manage our affairs wisely, confined forever to planet Earth. But this is not a likely scenario judging by the successful past evolution of mankind. The energy which would be available on Earth from Space is but the first step to help overcome the physical limitations which our civilization would be subjected to if we let dwindling resources on Earth determine our social structure and the institutions which serve our needs. Energy from Space could break open the closed ecological system of planet Earth and assure that resources will be available to sustain the economic and cultural requirements of a global population whose insistent demands for an improvement in living standards may otherwise be very difficult to meet. Although we have not yet used up the resources available on Earth, the dynamic growth which was built on a century-long exploitation of cheap and abundant energy supplies appears to be at an end. Within our grasp, we have not only the energy potential in Space, but the promise of an extraterrestrial industrial capability. There is increasing confidence that with the presently known space technology, we could utilize the resources of the Moon — oxygen, silicon, and aluminum — as raw mate-
rials which could be converted not only into construction materials to build the SPS, but also to construct industrial complexes which no longer would need to depend exclusively on Earth’s resources to meet terrestrial needs. The use of Space as an industrial site could have a revolutionary impact by making it possible to create new materials and to assemble unique structures extending over huge areas which are not subject to the destructive forces of gravity, wind, rain, and snow that act on any structure on Earth — the inevitable elements of the active terrestrial environment. .The Technical Challenges Evolution of the SPS Reference System. Preliminary studies of the SPS concept were performed at Arthur D. Little, Inc., from 1968 to 1972. During this time, the SPS concept was discussed at scientific and professional society meetings. In 1972, the Solar Energy Panel outlined a program plan for the SPS R&D program and suggested funding levels (5). In 1972, Arthur D. Little, Inc., joined with Grumman Aerospace, Raytheon Company, and the Spectrolab Division of Textron to evaluate the feasibility of the SPS concept on behalf of NASA (6). In this feasibility study, a baseline design was adopted to provide a power output of 5 GW on Earth. In addition to structural design and control, RFLavoidance techniques were investigated and key technological, environmental, and economic issues were identified. The results of this study encouraged NASA's Johnson Space Center and Marshall Space Flight Center to start extensive system definition studies with the help of Boeing Aerospace (7) and Rockwell International (8). In 1976, the Energy Research and Development Administration was assigned responsibility for the SPS program. A task group was formed; it recommended that the SPS concept be evaluated, and outlined a program for this purpose (9). In 1977, the Department of Energy and NASA approved the SPS Concept Development and Evaluation Program Plan (10) with the objective: “to develop by the end of 1980 an initial understanding of the technical feasibility, economical practicality, and the societal and environmental acceptability of the SPS concept.” Solar Energy Conversion. As originally conceived, an SPS can utilize current approaches to solar energy conversion, e.g., photovoltaic and thermal-electric, and others likely to be developed in the future. Among these conversion processes, photovoltaic conversion represents a useful starting point because solar cells are already in wide use in satellites. An added incentive is the substantial progress being made in the development of low-cost, reliable photovoltaic systems and the increasing confidence in the capabilities of achieving the required production volumes. Because the photovoltaic process is passive, it could give the SPS an operating lifetime of at least 30 years and, with scheduled maintenance, perhaps even several hundred years. Micrometeoroid impacts are projected to degrade 1% of the solar cell array area over a 30-year exposure period. Because of the lesser probability of impact, larger meteoroids are less likely to affect the solar cell array. Several photovoltaic energy conversion configurations applicable to the SPS concept are being considered (11). For purposes of comparison and assessment, two versions of an SPS reference system design have been adopted by NASA (12). For these configurations, silicon and gallium arsenide solar cells, with and without concentrators, could be used (13). For use in the SPS, the solar cells will have to be reasonably efficient, of low mass per unit area, and radiation-resistant during transit to and in operation in GEO. They
will have to be producible at rates and in volumes consistent with an SPS deployment schedule. To extend the lifetime of the solar cells, annealing methods could be utilized to eliminate or reduce the degrading effects of accumulated radiation exposure. Advanced photovoltaic materials could be used to form thin-film solar cells which would significantly reduce material requirements and the mass of solar cells and permit mass production at rates far greater than could be achieved by producing single-crystal solar cells. Technology Options for Power Transmission to Earth (11,12,13). To transmit the power generated in the SPS to Earth, there are two optional transmitting methods: • A microwave beam, or • A laser beam. Microwave Power Transmission. Free-space transmission of power by microwaves is not a new technology. In recent years, it has advanced rapidly and system efficiencies of 55%, including the interconversion between d.c. power and microwave power at both terminals of the system, are being obtained. The application of new technology is projected to raise this efficiency to almost 70%. The devices which are being considered for converting d.c. voltage to rf power at microwave frequencies in the SPS are crossfield amplifiers (amplitrons) and linear beam devices (klystrons). Microwave solid-state power transistors also are being investigated, as it appears feasible to combine them with solar cells in a sandwich power panel to form a resonant cavity feeding to waveguides. Considerations of mass, cost, and efficiency at specific frequencies have led to the selection of a frequency within the industrial microwave band of 2.40 to 2.50 GHz for the SPS reference system. The transmitting antenna for the SPS reference system is designed as a circular, planar, active, phased array having a diameter of about one kilometer. Space is an ideal medium for the transmission of microwaves; a transmission efficiency of 99.6% is projected after the beam has been launched at the transmitting antenna and before it passes through the upper atmosphere. To achieve the desired high efficiency for the transmission system while minimizing the cost, the geometric relationships between the transmitting and receiving antennas indicate that the transmitting antenna should be about one kilometer in diameter; the receiving antenna should be about ten kilometers in diameter. The power density at the receiving antenna will be maximum at the middle and will decrease with distance from the center of the receiver. The exact size of the receiving antenna will be determined by the radius at which the collection and rectification of the power becomes marginally economical. The transmitting antenna is divided into a large number of subarrays. A closed- loop, retrodirective-array, phase-front control could be used with these subarrays to achieve the high efficiency, pointing accuracy, and safety essential for the microwave beam operation. In the retrodirective-array design, a reference beam is launched from the center of the receiving antenna and is received at a phase comparator at the center of each subarray and also at the reference subarray in the center of the transmitting antenna. The receiving antenna is designed to intercept, collect, and rectify with high efficiency the microwave beam into a d.c. output. The d.c. output can be designed to either interface with high-voltage d.c. transmission networks or be converted into 60-Hz alternating current. The receiving antenna consists of an array of elements
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