SPACE SOLAR POWER REVIEW Volume 5, Number 2, 1985 Special Issue: Space Energy Symposium PERGAMON PRESS New York / Oxford / Toronto /'Paris/ Frankfurt I Sydney
SPACE SOLAR POWER REVIEW Published under the auspices of the SUNSAT Energy Council Editor-in-Chief Dr. John W. Freeman Space Solar Power Research Program Rice University, P.O. Box 1892 Houston, TX 77251, 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 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: Jean S. McHenry Editorial Office: John W. Freeman, Editor-in-Chief, Space Solar Power Research Program, Rice University P O Box 1892, Houston, TX 77251, USA.
Selected Papers from the 3rd Space Energy Symposium of the Institute of Space and Astronautical Science March 26, 1984, Tokyo, Japan Guest Editor: Makoto Nagatomo A Special Issue of SPACE SOLAR POWER REVIEW Pergamon Press New York • Oxford • Toronto • Paris • Frankfurt • Sydney
Copyright © 1985 Pergamon Press Ltd. ISSN 0191-9067 ISBN 0 08 032778-8 Published as Volume 5, Number 2, 1985 of Space Solar Power Review, and supplied to subscribers as part of their subscriptions. Also available to non-subscribers.
SPACE SOLAR POWER REVIEW Volume 5, Number 2 1985 Special Issue: Space Energy Symposium CONTENTS Makoto Nagatomo 119 Introduction Takashi Abe 121 Laser Propulsion Test Onboard Space Station Kyoichi Kuriki Saburo Adachi 127 Theoretical and Experimental Study on Rectenna Yasushi Shimanuki Array for Microwave Power Transmission H. Arashi 131 A Solar-Pumped Laser on the Space Station Y. Oka M. Ishigame Shintaro Hayashi 135 Solar Cell and Its Application Akira Onoe N. Higuchi 143 Cryogenic Power Distribution on a Space Power I. Ishii Station I. Kudo Y. Kimura Kiyohiko Itoh 149 Fundamental Study on SPS Rectenna Printed on a Yasuhiro Akiba Sheet of Copper Clad Laminate Takeo Ohgane Yasutaka Ogawa N. Kaya 163 Microwave Energy Transmission Test toward the SPS H. Matsumoto Using the Space Station S. Miyatake I. Kimura M. Nagatomo continued next page indexed in Current Contents, Eng. Ind. Monthly and Author Ind., Energy Res. Abstr., Energy Data Base, Int'l Aerospace Abstr. ISBN 0-08-032778-8 ISSN 0191-9067 (611)
T. Kida 171 A Preliminary Study on Decentralized Control of Y. Ohkami Large-Scale Flexible SPS Ken Kikuchi 179 Fundamental Study of Fuel Cell System for Space Toru Ozeki Vehicle Yasunobu Yoshida Yuko Fujita Hisashi Kudo Isao Kudo 189 Space Semiconductor Processing Factory Hiroyuki Fujisada K. Kuriki 197 Space Energetics and Environment Laboratory M. Nagatomo (SEEL) T. Obayashi Kuzuo Maeno 207 Advanced Scheme of Co2 Laser for Space Propulsion Yoshihiro Nakamura 213 Electric Propulsion Test Onboard the Space Station Kyoichi Kuriki Nobuhiro Tanatsugu 221 A Conceptual Design of a Solar-Ray Supply System in Masamichi Yamashita the Space Station Kei Mori Takio Tomimasu 231 Proposals for Test Operation of Electron Linacs on a Space Station and Radiation Processing of the Eruption Cloud Materials Using Electron Beams from Linacs Y. Yamashita 235 Concept of SPS Offshore Receiving Station and H. Hashimoto Potential Sites 243 Announcement I Software Survey Section
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUNSAT Energy Council INTRODUCTION This issue of Space Solar Power Review contains most of the papers presented at the 3rd ISAS Space Energy Symposium held on March 26, 1984. As the title of the meeting suggests, the symposium is sponsored and held regularly by the Institute of Space and Astronautical Science (ISAS), the Ministry of Education, Science and Culture. The presentations were made in Japanese, but the proceedings were written in English for the convenience of overseas colleagues. First of all, on behalf of the contributors and the symposium coordinators, I would like to express our appreciation to Dr. Peter Glaser and Prof. John Freeman for the kind invitation to publish the papers more completely in the Space Solar Power Review. Some authors have taken advantage of this opportunity to rewrite their papers which were too condensed in the limited pages for inclusion in the original proceedings. The efforts of Prof. Freeman to overcome the difficulty of written communication with many of the authors through improvements of their manuscripts are especially acknowledged. The 3rd Symposium consisted of three sessions: space station, spacecraft power system, and solar power satellite, but the space station session dominated the others in the number of papers presented. Obviously the space station is considered to be the most important step for energy related research in space. Fortunately, the symposium is attracting the interest of more researchers in Japan every year and the papers represent the activities in our country. In this sense, it is becoming a regular opportunity for information exchange. I believe this issue expands the opportunity to an international scale. Prof. Makoto Nagatomo Space Power System Section Institute of Space and Astronautical Science
digitized by the Space Studies Institute ssi.org
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUN SAT Energy Council LASER PROPULSION TEST ONBOARD SPACE STATION TAKASHI ABE and KYOICHI KURIKI Institute of Space and Astronautical Science Komaba 4-6-1, Meguroku Tokyo,Japan Abstract — A laser propulsion system (LAPS) onboard the Space Station (SS) is studied. In this system, the laser power is supplied from the laser system onboard SS to a subsatellite being deployed from SS. The satellite can control its orbital transfer by converting the laser power to a thrust. The technology for the system is reviewed and the LAPS test onboard SS is proposed. INTRODUCTION The mission of the orbital transfer from low Earth orbit (on which Space Station (SS) is constructed) to the other orbit (e.g., the geosynchronous Earth orbit) is highly desired. These missions require a thruster having the following qualities: 1) high Isp, 2) high reliability, and 3) light weight. The laser propulsion system (LAPS) is a candidate for these missions. In fact, it can have a high Isp (500 sec-2000 sec) (1), in comparison with a conventional chemical rocket (Isp ~ 400 sec) (see Fig. 1) (1). Furthermore, the system becomes simple and lightweight, since the laser power as an energy source is transferred remotely. In this article, we review the technology for LAPS and propose a LAPS test onboard the SS. REVIEW OF TECHNOLOGY FOR LAPS Laser Power Transmission Figure 2 shows the relation between the radius of the transmitter (Df the receiver (Dr), and the beam transmission range (2). This relation is determined by the defraction limit. As can be seen from this figure, the electromagnetic wave having a shorter wavelength is desirable for the larger transmission range, for fixed values of Dt and Dr. Thruster for Laser Propulsion In Fig. 3, two types of the thruster structures are shown schematically (1). In the one-port type engine, a laser beam is introduced from the nozzle exit, while, in the two-port type engine, a laser beam is received at first and is introduced into the absorption chamber. In both of them, the laser energy is absorbed mainly by the
Fig. 1. Enthalpy increase (hc) required to attain ideal specific impulse (/SD). m„is an atomic mass of hydrogen. Fig. 2. Transmitter/receiver diameter product as a function of transmission range R. X is a wavelength.
Fig. 3. Schematic figure for laser engine, (a) Single-port engine, (b) Two- port engine. inverse bremstrahlung, when the temperature of the fuel gas increases up to 104°K and the fuel gas is ionized. For absorption at lower temperature, we must consider a seeding of alkali metal, or a molecular absorption. As for a laser beam, two types of operation are considered: One is a repetitive- pulsed type (RP) and another is a continuously-working type (CW). In one-port type engine, RP operation must be employed (3) because of the absorption geometry. Unfortunately, it is expected that the mission for a subsatellite having the thruster of this type is limited, since the beam direction is limited. In the two-port type engine, both of the laser operation (RP or CW) can be operative. However, in CW operation, the absorption region may not be maintained steadily, since the absorption region has a possibility of being unstable when the inverse bremstrahlung is a main absorption mechanism (1). To overcome the instability, the irradiation of laser light must be stopped before the instability grows. Hence the laser light with an appropriate repetition time is favorable, although much study is necessary at this point. Furthermore, in a view point of a flexible mission attainability, a two-port type thruster is also favorable. LAPS TEST ONBOARD SS System Configuration In LAPS, the system is composed mainly of two parts. One is the subsatellite with the thruster for the laser propulsion including a receiver for a laser beam. The other is a system for the generation and transmission of laser power, including a beam guidance system and the thermal control system (see Fig. 4). The power is supplied from SS through a SS bus, and the thermal control system (TCS) works under the TCS of SS. The beam guidance system guides the main beam to the receiver of the subsatellite.
Fig. 4. System configuration of LAPS onboard the SS. (a) Schematic figure of the system, (b) Block diagram of the system. System Performance Considering the beam transport characteristics and the thruster dynamics, we propose the LAPS with a performance shown in Table 1. In this table, a CO2 laser is chosen, because of its capability for large power generation, although the laser beam with shorter wave length is desirable for a larger transmission range. As for the radius of the transmitter and the receiver for the laser beam, we assume the beam transmission range as about 50 km. The subsatellite can move around in the region having the distance 50 km from the SS. The temperature at the absorption chamber and the mass flow rate of the fuel are assumed to 1.8xlO5°K and 3.1 X10-5 kg/s, respectively. As for a propellant, a conventional fuel is employed, considering the case that LAPS does not work well. Since a conventional fuel has a greater molecular mass, and gives a lower Isp, much research is necessary for the future.
CONCLUSION We propose that the LAPS be tested onboard the SS. This system can be applied to the orbital transfer vehicle (OTV) in future. The technology for this system is divided into two parts. One is the laser beam generation and its transport, and another is the thruster for the laser propulsion. The former is also important for the power transportation technology when the electric power generation is considered instead of the thruster. As for both of them, much more development remains to be done. REFERENCES 1. H.H. Legner and D.H. Douglas-Hamilton, CW Laser Propulsion, J. Energy, 2, 85, 1978. 2. P.F. Holloway and G.L. Bernard, Utility of and Technology for Control Power Station, A1AA-81-0449. 1981. 3. R.F. Weiss, A.N. Pirri, and N.H. Kemp, Laser Propulsion, Aeronaut. Astronaut., 50-58, 1979.
digitized by tthe Space Studies Institut ssi.org itue ssiorg
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUNSAT Energy Council THEORETICAL AND EXPERIMENTAL STUDY ON RECTENNA ARRAY FOR MICROWAVE POWER TRANSMISSION SABURO ADACHI and YASUSHI SHIMANUKI Faculty of Engineering Tohoku University Sendai, Japan Abstract — In this paper, we describe a theoretical and experimental study on a rectenna array for microwave power transmission. The conversion efficiency of microwave energy to DC and a spurious radiation of harmonics generated by the rectenna were theoretically investigated. Furthermore, we actually composed the rectenna and measured the conversion efficiency. It was shown that our experimental results agree with the theoretical results. INTRODUCTION A receiving antenna used for microwave power transmission is generally called a rectenna. As an antenna element, various types of antennas have been considered (1,2). In this paper, we deal with a half-wave dipole antenna array above a reflecting plane as a rectenna. This system consists of a large number of rectenna elements, each of which converts the incident microwave energy to DC. Each rectenna element includes a Schottky-barrier diode to rectify microwave energy, an input filter to suppress the spurious radiation of harmonics, and an output filter to pass the DC component only. It is necessary for such rectenna to suppress a spurious radiation of harmonics generated by the diode to a sufficiently low level, and to have a high RF-DC conversion efficiency. It is also important to construct the necessary microwave circuits as compact as possible. For the above reasons, we fabricated the conversion circuits by means of microwave integrated circuit technique. THEORY To estimate the theoretical conversion efficiency from RF energy to DC energy and the spurious radiation of harmonics, each rectenna element is represented by an equivalent circuit. The conversion efficiency and the spurious radiation are obtained numerically by solving the nonlinear circuit equation by the Newton-Raphson iteration method (3). The input impedance of the rectenna element was obtained by assuming an infinite planar half-wave dipole array above a perfectly conducting plane (4). The numerical examples of the conversion efficiency and the spurious radiation of harmonics are shown in Fig. 1 and Fig. 2, respectively.
Fig. 1. Conversion efficiency versus load resistance. Fig. 2. Spurious radiation of harmonics versus load resistance. Fig. 3. Rectenna array above a reflecting plane. Fig. 4. Conversion circuit unit. Fig. 5. Experimental conversion efficiency versus load resistance.
Fig. 6. Experimental conversion efficiency versus incident power. EXPERIMENTS A rectenna array used in this experiment is shown in Fig. 3. The conversion circuit unit is shown in Fig. 4. The conversion unit was fabricated by means of connecting a diode on a thin film circuit fabricated by microwave integrated circuit technique. An array antenna is composed by arranging 69 dipole antenna elements above a reflecting plane. The filter and diode unit was connected to a center element of the array only. The remaining elements were terminated by the input impedance of the element antenna, about 100 fl resistance. The conversion efficiency of the rectenna array per unit element was measured by comparing the obtained DC power of one rectenna with the maximum available receiving RF power of each antenna element. The measured conversion efficiencies are shown in Fig. 5 and Fig. 6. The calculated values in Fig. 5 and Fig. 6 are the simulation results based on some parameters of the diode used in this experiment. CONCLUSION The rectenna array for microwave power transmission has been investigated theoretically and experimentally. The conversion efficiency to DC energy and the spurious radiation of harmonics generated by the rectenna have been theoretically clarified. The conversion efficiency was measured for the experimental rectenna array model, and was found to agree approximately with the theoretical prediction. REFERENCES 1. R.J. Gutmann and J.M. Borrego, Power Combining in an Array of Microwave Power Rectifiers, IEEE Trans. MTT 27, 958-968, 1979. 2. Y. Akiba, Y. Ogawa, and K. Ito, On a Rectenna Module for SPS Reception by Use of a Circular Microstrip Antenna, Tech. Rep. IECE Japan AP 83-55, 37-41, 1983. 3. M. Kanda, Analytical and Numerical Techniques for Analyzing an Electrically Short Dipole with a Nonlinear Load, IEEE Trans. AP 28, 71-78, 1980. 4. Y. Shimanuki and S. Adachi, Conversion Efficiency to DC Energy and Spurious Radiation of Harmonics from a Receiving Antenna for Microwave Power Transmission. Tech. Rep. IECE Japan, AP 83-88, 49-56, 1983.
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUNSAT Energy Council A SOLAR-PUMPED LASER ON THE SPACE STATION H. ARASHI, Y. OKA and M. ISHIGAME Research Institute for Scientific Measurements Tohoku University 1-1, 2-chome, Katahira Sendai, Japan INTRODUCTION A laser light source is indispensable in space for optical communication, laser propulsion, energy conversion and laser processing, etc. Concentrated solar radiation can be used to optically excite a laser medium. A laser which is directly excited by solar radiation is called a solar-pumped laser. In a solar-pumped laser system, a high conversion efficiency of energy is expected because of direct photon-photon conversion. In addition, an available energy source in space is limited to solar energy. Therefore, a direct conversion of solar radiation into coherent laser light is one of important space technologies. The mission objective is to test the operation of a solar-pumped laser in space. A solar-pumped laser is classified into two types according to the employed laser medium — one a solid-state laser, the other a gas laser. A SOLAR-PUMPED SOLID-STATE LASER A solar-pumped solid-state laser with several hundred W output power is profitable for optical communication in space because the problem of recharging of the laser medium does not occur. We have examined on the Earth a solar-pumped Nd:YAG laser by using a 10 m aperture paraboloidal solar concentrator equipped in the Solar Energy Laboratory of our Institute (1). The experimental setup of our solar-pumped Nd:YAG laser is shown in Fig. 1. The maximum output power of our laser has exceeded 18 W in multi-mode, which is the highest power so far reported on solar- pumped lasers. On the basis of these experimental results, we construct a solar-pumped solidstate laser to be used on the space station. In first mission phase, the paraboloidal solar concentrator, 2 m in aperture, will be mounted on the space station via a two-axis gimballed sun-orientation mechanism as shown in Fig. 2. Using this concentrator, a solar-pumped solid-state laser will be tested to estimate a stability of mode- locked operation which is required for optical communication. The optimization of laser pumping optics will be also examined to increase the conversion efficiency. In this laser system, the laser rod must be placed at the focal point of the concentrator to be efficiently pumped by concentrated solar radiation. Hence, the direction of the laser beam is fixed by the orientation of the concentrator. To remove this restriction, in the second mission phase, a solar radiation concentrated by free-flyer type parabolic mirror will be transferred to the laser pumping
Fig. 1. Experimental setup of a solar-pumped Nd:YAG laser examined on the Earth: 1, Paraboloidal mirror; 2, Solar radiation; 3, Water-cooled Nd: YAG laser rod (4 mm in. diam and 75 mm in length); 4, Totally reflecting mirror; 5, Output mirror; 6, Detector; 7, IR-viewer; 8, He-Ne laser for optical alignments. Fig. 2. A solar-pumped solid-state laser system mounted on the station: 1, Solar radiation; 2, Paraboloidal solar concentrator; 3, Cooled laser rod; 4, Totally reflecting mirror; 5, Output mirror; 6, Laser beam; 7, Orientation mechanism. optics by using a flexible optical fiber as shown in Fig. 3. With this improved laser system, the laser head can be located independently from the orientation and position of the parabolic mirror. Therefore, we can use a coherent laser light at any desired place in the space station.
Fig. 3. A solar-pumped solid-state laser system using a free-flyer type paraboloidal solar concentrator: 1, Solar radiation; 2, Paraboloidal solar concentrator; 3, Secondary mirror; 4, Orientation mechanism; 5, Flexible optical fiber; 6, Solar radiation for pumping; 7, Cooled laser rod; 8, Totally reflecting mirror; 9, Output mirror; 10, Laser beam. A SOLAR-PUMPED GAS LASER In order to increase output power of a solar-pumped laser, a large amount of solar energy must be collected by using a huge paraboloidal concentrator with a large focal length. As a focal length of a concentrator becomes large, a diam of the Sun's image also becomes large. Therefore, in a solar-pumped laser, a laser medium with large volume is necessary to increase output power. From this requirement, a gas laser medium is most profitable. To construct a solar-pumped gas laser with large output power usable in space, we must search for a suitable gas laser medium which can be used reversibly with a high conversion efficiency of energy. The construction and deployment of a huge solar concentrator are also important technologies to be developed. REFERENCE 1. H. Arashi, Y. Oka, N. Sasahara, A. Kaimai, and M. Ishigame, A Solar-Pumped cw 18 W Nd:YAG Laser, Jpn. J. Appl. Phys. 23, 1051, 1984.
digitized by the Space Studies Institute ssi.org
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUNSAT Energy Council SOLAR CELL AND ITS APPLICATION SHINTARO HAYASHI and AKIRA ONOE Electron Device Engineering Laboratory Toshiba Corporation 8, Shinsugita-cho, Isogo-ku Yokohama, 235 Japan Abstract — The outline of solar cell technology and the photovoltaic industry are presented for terrestrial use. Then, some new technologies on space-use solar cells are shown. It seems that there is a close relationship between the growth of terrestrial and space-use solar cell technology, and in order to realize a large scale SPS, terrestrial solar cells should have been put into practice. INTRODUCTION At the first ISAS Space Energy Symposium held on the 28-29th of January, 1982, we reported the results of the comparison between terrestrial and SPS-use solar cell (1). It was emphasized that in order to realize 5-15 GW SPS, cost decreases of solar cells by several orders of magnitude and development of large scale mass production technology, are most important. Also, we showed several attempts to realize the improvement of producibility. Now we shall describe the activities hitherto accomplished regarding terrestrial use solar cells in Japan and in the world. Then we shall show several areas of progress in space-use solar cell technology. DEVELOPMENT PROGRAMS ON PHOTOVOLTAIC TECHNOLOGIES Sunshine Program in Japan Photovoltaic energy has been expected as a renewable and clean energy which is thought to occupy the main part of 21st century energy supply. In Japan, under the leadership of MITI and NEDO, several development programs have been carried out by many kinds of research organizations. These programs are all headed under the title Sunshine Program. Especially, NEDO executes an experiment on overthrough pilot production line of low cost solar cells and their demonstrative application systems. The pilot production line has the capacity of 500 kW per year and consists of one chlorsilane purifying plant, one SOG polysilicon granulating plant, two wafer manufacturing plants (ribbon and cast wafer), two solar cell processing plants (dry and wet processing) and one panel assembly plant. Meanwhile, five kinds of demonstrative application systems have been under construction, namely, private home application system, co-operative residence system, college power supply system,
industrial power supply system and concentrated power generation systems. Each of these demonstration systems are designed as 3 kW, 60 kW, 200 kW, and 200+ 1000 kW, respectively. Construction of a pilot production line started in October, 1980 and was accomplished by March, 1984. A demonstration experiment will be carried out until March, 1985 (6). In addition to these crystalline Si solar cell pilot plant and demonstration systems, a research and demonstration plant on amorphous Si solar cell technology has been intensely carried out. National Photovoltaic Plan in USA The Department of Energy (DOE) has proposed a Five Year Research Plan from 1984-1988 on photovoltaics (2). The principal research items are materials, collectors and systems. Regarding materials research, single junction thin films such as CdS- like polycrystalline thin film cells, amorphous Si cells and GaAs-like thin film cells, multijunction cells of crystalline or amorphous materials, some innovative materials, low cost high purity Si materials and advanced Si sheet technology are going to be treated. Regarding collector research, flat collector and concentrated collector research will be carried out. Regarding systems research, module reliability, array technology and system experiments have been planned. Regardless of the recession, a lot of research items are going to be developed. SOLAR CELL TECHNOLOGY Mission of Each Technology In Table 1, the expected mission for several kinds of solar cell technologies are summarized. Beyond the first generation of special use, we are thought to lie in the second generation of advanced CZ Si technology, and if we can succeed at the technical innovation by adopting advanced ribbon crystalline technology, then we expect to enter the third generation, where industrial use of photovoltaic energy begins. Furthermore, the fourth generation where grid connection of photovoltaic power generation will be realized may be expected by amorphous Si technology and so on. The prospect of photovoltaic system cost decrease by the DOE was shown in Fig. 1 (3). This prospect demonstrates that the replacement of conventional energy by solar cell may be possible only when system cost is lowered to under $1/Wp. Crystalline Si Solar Cell Technology In order to avoid the slice loss of Si ingot and lower the wafer cost, several kinds of ribbon crystal manufacturing technologies have been developed. Among them, Si ribbon pulling technology using die lies nearest to practice and 100 mm width ribbon crystal has already been obtained. Edge supported pulling is thought to be a more advanced technology. Using ribbon crystal, more than 12% of conversion efficiency has been reported (4).
TABLE 1 MISSION OF EACH KIND OF SOLAR CELLS________
Fig. 1. Cost prospect for solar cells in near future (DOE). On the other hand, for the purpose of improving mass producibility, several cast Si technologies have been attempted. Among them, the heat exchange method to obtain large grain size polycrystal and spin method of molten Si (5) are quite unique. Amorphous Si Solar Cell Technology The amorphous Si solar cell is expected for the future photovoltaic power source because of its potential excellence at the point of low consumption of resource and high producibility. The amorphous Si solar cell requires only 0.5-1.0 /rm in thickness because of its considerably high absorption coefficient of light. It is made by plasma CVD method, which is widely used in semiconductor industry, using silane gas. The main items for development are an increase of conversion efficiency, an improvement of reliability and the pursuit of high speed deposition technology. Tandem structure solar cell development, doping of fluorine and disilane CVD technology are now in development. The value of conversion efficiency increases markedly year by year as shown in Fig. 2. Recent reports show the efficiency more than 10% for small area solar cell (13). PROSPECT FOR THE GROWTH OF PHOTOVOLTAIC INDUSTRY In Japan, 3-4 MWp of solar cell has been thought to be manufactured in fiscal year 1983. Among these, the entertainment use of solar cells such as for electronic handy calculator-use occupies the main part, which is a marked feature of the Japanese
Fig. 2. Progress of the amorphous silicon solar cell efficiency as of December 1982. An example of the remarkable advance in the amorphous semiconductor technology. photovoltaic industry. The growth rate has continued to be 100% for the last several years. On the other hand, the worldwide gross output of solar cells is estimated to be about 20 MWp in FY 1983 and expected to grow by 60% per year until it reaches to 400 MWp in 1990. Furthermore, in the year 2000, about 10 GWp of solar cell is thought to be manufactured (14). Of course the necessary condition for the realization of this growth will be technical innovations as mentioned before. It must be noted that even in 2000 we can hardly obtain the amount of solar cells sufficient for 15 GW SPS. SOME EXAMPLES OF SOLAR CELL APPLICATIONS The DOE has reported a conceptional diagram of the development of solar cell application as shown in Fig. 3 (15). NEDO's demonstrative application systems can
Fig. 3. Cost reduction and market growth of solar cell. be seen to include typical fields at advanced stage. The current situation lies at the boundary region between public use and industrial use. As for the stand alone power supply, the solar powered water pumping system belongs to batteryless application, while village power, relay terminal power supplies, street lighting systems, etc., require battery back-up. On the other hand, many experimental systems which are connected to grid line have been constructed for the purpose of energy conservation. In the USA, a solar power generation station of 16.5 MWp capacity has been under construction. INTERNATIONAL CO-OPERATION International co-operation on solar cell technology has become markedly promoted. According to the SUMMIT agreement, Japan is expected to play a leading roll. On the other hand, IEC has decided to establish TEC/TC82 (Solar Photovoltaic Energy Systems), where international standards for photovoltaic power generation system and all the elements included in the system are going to be treated. TEC/TC82 has three working groups dealing with glossary, module and system, respectively. These activities show that the photovoltaic industry will grow steadily to become one of the substantial industries. SOME EXAMPLES ON PROGRESS OF SPACE-USE SOLAR CELL TECHNOLOGY The targets of research on space-use solar cell are an increase of efficiency, a lightweight cell, and cost decrease and improvement of radiation damage. In order to
decrease the weight of cell, the thickness of Si wafer is going to be lessened from 200-50 gm (7). Radiation damage is found to be decreased by doping B or by decreasing O content (8). Furthermore, as the material which suffers less damage by radiation and enables higher conversion efficiency, InP has been studied in addition to GaAs. Less than 20% of efficiency degradation after fluenced by 101K gammaphotons per square centimeters was reported (9). As for low cost technology, large area cell (2x2, 2x4 to 5x5 cm2) and improved interconnection are now being studied (10). The single crystalline Si solar cell shows an efficiency up to 15%, while the GaAs tandem cell is said to approach 25-30%. An ultra-thin GaAs epitaxial cell which has a thickness of about 10 /z has been reported (11). A quite unique attempt to pursue 50% efficiency is being investigated. The concept of the "Plasmon” cell consists of the conversion of solar radiation energy over a full range of spectrum into electron surface waves on metal and power extraction through nonelastic tunneling pn junction (12). CONCLUSION Terrestrial and space-use solar cell technology apparently seem to grow separately. But there is a close influence that is hidden between them. Foremost technologies created in space-use solar cell have hitherto improved the terrestrial cell. But in the future, the reverse influence, namely, the introduction of mass production technology to space-use cell manufacturing, the application of evaluation methods of terrestrial solar cell and the realization of ultimate low cost cell by using innovative terrestrial solar cell technology will appear according to the establishment of solar cell industry background. REFERENCES 1. S. Hayashi, A. Onoe, and T. Kato, Photovoltaic Industry and Possible Seeds for SPS Solar Cells, Proc. 1st ISAS Space Energy Symp., 83-88, 1982. 2. National Photovoltaic Program, Five Year Research Plan, Dept, of Energy. 3. P.D. Maycock, Overview-Cost Goals in the LSA Project, 14th IEEE Photovoltaic Specialist Conf., pp. 6-12, San Diego, CA, 1980. 4. J.B. Milstein, R. W. Hardy, and Y.S. Tsuo, Research on Polycrystalline Silicon Solar Cells: Goals and Accomplishments, 16th IEEE Photovoltaic Specialist Conf., pp. 119-122, San Diego, CA, 1982. 5. Y. Maeda, T. Yokoyama, and I. Hide, Large Area Silicon Sheet Produced by the Spinning Method, pp. 133-136, ibid., 1982. 6. K. Yamagami, S. Noguchi, K. Kurokawa, and T. Horigome, Conceptual Design of a 500 kW/Year Mass-Production Process of Low-Cost Silicon Solar Cell and Module, Internal. Solar Energy Soc., Solar World Forum, Brighton, England, E1A-1, 1981. 7. F. Ho and P.A. Iles, Recent Advances in Thin Silicon Solar Cells, 16th IEEE Photovoltaic Specialist Conf., pp. 156-159, Orlando, FL, 1982. 8. J.P. Mullin and D.J. Flood, NASA Space Photovoltaic Research and Technology Programs, Proc. 3rd Europ. Symp. Photovoltaic Generators in Space, pp. 121-126, Bath, England, 1982. 9. A. Yamamoto, M. Yamaguchi, and C. Uemura, High Conversion Efficiency and High Radiation Resistance InP Homojunction Solar Cells, Appl. Phys. Lett. 44, 611-613, 1984. 10. K.W. Matthei, D.K. Zemmrich, and M. Webb, Optimization of Large Area Solar Cells for Low Cost Space Application, 15th IEEE Photovoltaic Specialist Conf., pp. 228-234, Orlando, FL, 1981. 11. R.J. Boettcher, P.G. Borden, and M.J. Ludowise, Ultrathin GaAs and AlGaAs Solar Cells, 16th IEEE Photovoltaic Specialist Conf., pp. 1470-1473, San Diego, CA, 1982. 12. L.M. Anderson, Parallel-Processing with Surface Plasmons, a New Strategy for Converting the Broad Solar Spectrum, pp. 371-377, ibid., 1982. 13. Y. Hamakawa, Jarect, Vol. 6, Amorphous Semiconductor Technologies & Devices, pp. 1-8, Ohmsha Ltd., Japan, 1983. 14. H.W. Brandhorst and J.C.C. Fan, The Solar Electricity Future (Panel Discussion), 16th IEEE Photovoltaic Specialist Conf., pp. 1478-1484, San Diego, CA, 1982. 15. Dept, of Energy Summary Report, DOE/ER-0035, p. 14, 3 Feb, 1975.
digitized by the Space Studies Institute ssi.org
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUN SAT Energy Council CRYOGENIC POWER DISTRIBUTION ON A SPACE POWER STATION N. HIGUCHI, I. ISHII, 1. KUDO and Y. KIMURA Electrotechnical Laboratory 1-1-4 Umezono. Sakura, Niihari Ibaraki, 305 Japan Abstract — A power distribution system on a 5 GW space power station (SPS) is proposed, utilizing a low voltage DC superconducting (SC) cable system. The electric power generated at the solar cells is collected up to 4 kV 10 kA by means of aluminum bus bars, and fed to the converting system through the SC cable system. The maximum current of the bus bars is determined by minimizing the summation of the Joule losses and the refrigerating load. The superconductor is aluminum stabilized NbTi, and the negative and positive conductors are laid coaxially to suppress the magnetic field outside the cable. The cable is designed to be compact for easy transportation by the space shuttle. The dimensions of the cable are varied depending on the rating. The largest diameter is 130 mm (5.1 in.) at the rating of 4 kV 250 kA. Its thermal insulation, consisting of blankets of multilayer insulation and a proper radiating system, needs no vacuum vessels in the space environment. The power for refrigerators is estimated as up to 19 MW, and its total weight is 7x IO5 kg (1.5x 106 lbs), but improvement can be expected. It is concluded that the proposed SC cable system provides a better efficiency and lower lift-off weight to the station, in comparison with the values of systems of normal conductors. INTRODUCTION A space power station is one of the most attractive solutions to the energy problem because it provides huge and absolutely clean power. It seems difficult to realize a practical SPS in this century, however, we have to continue to make efforts to improve its subsystems. The authors tried to investigate the application of a SC cable system to the reference model by NASA/DOE, rating 5 GW at the ground. According to an estimation, it is necessary to generate 10 GW on a SPS to obtain 5 GW at the ground. It is of great importance to design highly efficient subsystems. However, no improvement can be expected in the power dissipation of the aerial system, which accounts for the major portion of the loss. Therefore, it is essential to obtain lower losses in the power distribution and conversion subsystems. A superconducting cable system is quite effective in this situation. DESIGN OF CABLE SYSTEM Direct current is chosen for the distribution system, and a relatively low voltage of 4 kV is selected as the rating, which makes the insulation simple at bus bars and minimizes the allowable bending radius of the cable. Consequently, the maximum
Fig. I. Location of SC cables and main bus bars. current totals 2.5 MA. This value of the current presents no problem for a SC cable system, but the allowable bending radius does. Cables will be wound on drums to reduce the number of connections. But the size of the drum is limited for the transportability by the space shuttle, and must be as small as possible. In the next step, the maximum current of bus bars must be decided, which is one of the major factors determining the efficiency of the subsystem. In order to reduce the Joule losses, the electric power collected from solar cells ought to be transported to SC cable system immediately. In this case, a large number of terminations are necessary. On the other hand, too many terminations are not desirable, from the point of the view of decreasing the load of refrigerators. Compromising with both of the Joule losses and refrigerating load reduction, it is decided to use 10 kA. The proposed location of SC cables and main bus bars is shown schematically in Fig. 1. The solar cell array of 10 km x 5 km consists of 25 sections of 2 km x 1 km, and each section has one termination of a SC cable circuit. Ten main bus bars of 4 kV 10 kA are connected to the termination. Each circuit consists of three SC cables for redundancy. The rating current of the designed cables is 1.5 times larger than the value required for ordinary operation, so that full power can be carried by two cables in case of the contingency of a failure in one of three.
Fig. 2. Cross sectional view of a DC SC cable rating 4 kV 250 kA. Each circuit of SC cable system has five terminations on the solar cell array, and its rating current increases at each termination. Dimensions of the cables are varied depending on the rating. Figure 2 shows the cross sectional view of the designed cable and a general description of its largest portion is shown in Table 1. The largest outer diameter is designed to be 130 mm (5.1 in.) and the allowable bending radius is estimated to be smaller than ten times that diameter. The selected superconductor is aluminum stabilized niobium titanium. The overall current density is designed to 250 A/mm2 at the rating. The positive and negative conductors are laid coaxially to suppress the magnetic field outside the cable, and enclosed in aluminum corrugated tubes, which will be used as the coolant ducts. The maximum electromagnetic force per unit area estimated at the inner conductor is 31 kgf/cm2 (440 psi), and these ducts must be strong enough to endure against this force. Although electric insulation by the coolant itself, supercritical helium, makes the cable connections simple, tape wrapped insulation is chosen to obtain smaller outer diameter.
Fig. 3. Thermal insulation for SC cable. The space environment is advantageous for thermal insulation, because no vacuum vessels are necessary for multilayer insulation. Moreover, thermal shield of cryogenic temperature is available with a proper radiator system. Consequently, the structure of thermal insulation can be simple. In this case, the shroud temperature is supposed to be 77 K (-321° F) for the estimation of the heat-in-leak. Figure 3 shows the conceptional view of the thermal insulation. The cable itself does not have thermal insulation layers and it will be laid surrounded by blankets of multilayer insulation installed on the shroud. Many merits can be counted in this structure, for example, smaller diameter of the cable, easier connecting and laying. The level of the orbit for the construction is not yet decided, but it can easily be carried out by robots because of the simplified coaxial structure of the cable. The connected cables can be laid without attention to the electromagnetic force and the environment, such as plasma, electric charge and so forth. REFRIGERATORS According to investigations performed so far, refrigerators seem inevitably to be vibrational heavy machines which need periodic inspection. And considering that large ones are absolutely but exclusively necessary for initial cooling down, it is beneficial to make a refrigerator compact combining its components, i.e., a compressor, heat exchangers, expanders, etc., into a unit for easy changeout. Large ones will be transferred to another SPS newly built on GEO to avoid unnecessary redundancy, and ordinary units which need maintenance will be brought down to LEO where human labor is available if necessary, and replaced with new ones. The power for refrigerators is estimated as up to 19 MW. Its main components, the load by the heat-in-leak at the cables and the one by the heat through the power leads, are almost comparable. The weight of this set of refrigerators of 19 MW is extrapolated to 7x 105 kg (1.5x 106 lbs) from ordinary ones used on the ground. It is so heavy for the use on a SPS that lighter ones must be designed specifically for the space use, but this should not be very difficult. Moreover, if low temperature compressors are available, not only the weight but also the power consumption will be improved greatly.
WEIGHT AND LOSSES OF ALUMINUM CONDUCTOR SYSTEMS Line Voltage (kV) 4 40 100 Weight of Conductors (kg) 2.8 x 107 2.8 x 10“ 1.1X 10s Conductor Loss (MW) 2,200 220 88 CONCLUSION It is concluded that the SC cable system provides much better efficiency and lighter weight than systems with ordinary conductors, by the comparison of the values described above with the results of the calculations shown in Table 2, wherein it is supposed that SC cable system is replaced by systems of aluminum conductors, with the line voltage of 4 kV, 40 kV and 100 kV and the current density of 3 A/mm2. At this density, a radiator system installed along the conductors is necessary, with a width of 1 m (3.3 ft) for every 20 kA to keep their temperature below 500 K (440° F). It is obvious from the comparison that the SC cable system is superior in both weight and the loss. Only systems of 100 kV or higher line voltage can be competitive, however, they are considered to involve difficulties in electric insulation in the space environment. Therefore, SC cable system is one of the best candidates for power distribution systems on SPSs. REFERENCES 1. P.E. Glaser, Power from the Sun: Its Future, Science 162, Nov. 1968. 2. G.M. Hanley, SPS Concept Definition Study, 5 Syst. Eng./Integration. Res. Technol., NASA CR- 3396, 1981. 3. I. Kudo, I. Ishii, Y. Kimura and N. Higuchi. Cryogenic Power Distribution on a SPS, Proc. 2nd. ISAS Space Energy Symp. II-6, 1983. 4. CRIEPI, Cryogenic Power Transmission (Research and Development of New Transmission System- II), 1973. 5. N. Ito, Electrical Characteristics of Superconducting Cable, Bui. Electrotech. Lab. 35, 161, 1971.
digitized by the Space Studies Institute
0191-9067/85 $3.00 + .00 Copyright ® 1985 SUNSAT Energy Council FUNDAMENTAL STUDY ON SPS RECTENNA PRINTED ON A SHEET OF COPPER CLAD LAMINATE KIYOHIKO ITOH, YASUHIRO AKIBA, TAKEO OHGANE and YASUTAKA OGAWA Department of Electronic Engineering Hokkaido University Sapporo 060 Japan Abstract — This paper proposes the use of a microstrip antenna as a competitor to the linear antenna for "Rectenna” in SPS (Solar Power Satellite) project. The microstrip antenna features high-Q and higher resonance-harmonics which are not integer multiples of the dominant resonance frequency if a circular microstrip antenna (CMSA) is chosen. This paper experimentally clarifies wide frequency band characteristics of the CMSA. It is especially shown that the CMSA with slits possesses an excellent higher harmonic suppression characteristic. The CMSA with slits is used as a receiving antenna, a higher harmonic rejection filter as an input filter, a diode bridge using four Toshiba 1SS154 Si Schottky diodes as a rectifier, a by-pass chip condenser as an output filter in the rectenna. The rectenna was built as a trial and its RF-DC conversion efficiency was measured. In the experimental results, the conversion efficiency is not high. However, the rectenna obtained in this paper has many unique and attractive properties — low in profile, light in weight, compact and conformable in structure, easy to fabricate, and easy adaptation to the photoetching technique in fabrication. INTRODUCTION The “Rectenna” receives microwave power (2.45 GHz) from SPS (Solar Power Satellite) and is an important basic element in the Earth Station Terminal in the SPS project. It has no previous counterparts in electric power engineering or microwave and antenna engineering. The name of the rectenna comes from a receivingrectifying antenna. The rectenna itself consists of a receiving antenna, low-pass filter and rectifying diode. The low-pass filter is used mainly for suppression of reradiation of higher harmonic microwaves, which are generated by the rectifying diode. The SPS baseline rectenna has been developed by Raytheon Company, where they have used a dipole antenna with ground plane as the receiving antenna (1). Gutmann et al. have investigated the possibility of using a printed circuit dipole with ground plane, and a printed circuit Yagi-Uda with or without ground plane, as the receiving antenna. All of the above mentioned antennas are known as linear antennas in antenna engineering (2). The linear antenna is generally featured by low-Q and higher resonance-harmonics of integer multiples of its dominant resonance frequency (2.45 GHz). These features are undesirable for suppression of higher harmonic re radiation. This paper proposes the use of a microstrip antenna as a competitor to the linear antenna for “Rectenna” in the SPS project. The microstrip antenna is featured by high-Q and higher resonance-harmonics which are not integer multiples of the domi-
Fig. 1. Block diagram of rectenna. nant resonance frequency if a circular microstrip antenna (CMSA) is chosen. This paper also experimentally clarifies wide frequency band characteristics of the CMSA. It is especially shown that the CMSA with slits possesses an excellent higher harmonic suppression characteristic (1). The block diagram of the rectenna in this paper is shown in Fig. 1. The CMSA with slits is used as a receiving antenna, a higher harmonic rejection filter as an input filter, a diode bridge using four Toshiba 1SS154 Si Schottky diodes as a rectifier, a by-pass chip condenser as an output filter in the rectenna. The rectenna of Fig. 1 was built as a trial, and its RF to DC conversion efficiency was measured. In the experimental results, the conversion efficiency is not high. However, the rectenna obtained in this paper has many unique and attractive properties — low in profile, light in weight, compact and conformable in structure, easy to fabricate, and easy adaptation to the photoetching technique in fabrication. CIRCULAR MICROSTRIP ANTENNA (CMSA) The general geometry of the microstrip antenna without feed is shown in Fig. 2. The microstrip antenna is often called a “patch” antenna because of its shape. The microstrip antenna has received much attention because of its many unique and attractive properties. It is low in profile, light in weight, compact and conformable in structure, easy to fabricate, easily integrated with solid-state devices, and easy to adapt to the photoetching technique in fabrication (2,3). All of these features are desirable for the receiving antenna of the rectenna. Moreover, eigenvalues which correspond to the resonance frequencies of the antenna can be controlled if a proper patch is chosen. For example, if a circular microstrip antenna (CMSA) is chosen, its eigenvalues are given by the following equation:
Fig. 2. General geometry of microstrip antenna without feed. The radiation characteristic of the CMSA is depicted as shown in Fig. 3. On the other hand, power spectra generated in full-wave rectification are shown in Fig. 4. The DC spectrum and even-numbered spectra of the dominant frequency (2.45 GHz) are generated as shown in Fig. 4. Therefore, it can be expected that there exists almost no higher harmonic reradiation from the CMSA. WIDE FREQUENCY BAND CHARACTERISTICS OF THE CMSA First, the CMSA matching to a 50 ohm feeder line atf0 = 2.45 GHz was printed on copper clad laminate whose dielectric constant Er is about 2.6. Return loss versus frequency is shown by a dotted line of Fig. 5 where frequency range is from 2 GHz to 12.4 GHz which means that data until 5 f0 (12.25 GHz) can be obtained. The figure shows that the CMSA has resonance frequencies in vicinity to 2f„ (4.9 GHz) and 3/0 (7.35 GHz). On the other hand, return loss for the dipole with ground plane is fairly low over the experimental frequency as shown in Fig. 5. The received power by the CMSA and dipole is shown in Fig. 6. The dipole receives the highest power over the entire frequency examined except in vicinity to 3/. The reason why this exception occurs can be explained using Fig. 7 where surface currents of three modes (TM110, TM010 and TM120) are depicted. The resonance frequencies of TM110, TM010 and TM120 are f0, 2.08 f0 and 2.9/0> respectively. Two modes (especially TM120) can be easily excited at 2.08 f0 2.9/0, respectively. In order to suppress TM010 and TM120 modes, slits are cut on the CMSA as
Fig. 4. Power spectrum of full-wave rectification. shown in Fig. 8 where directions of the slits coincide with the ones of current flow fot TM110 (dominant) mode so that the current of TM110 is not disturbed. The return loss and power obtained by this CMSA with slits are shown by solid lines in Figs. 5 and 6, respectively. TM010 and TM120 modes in vicinity to 2 f0 and 3 f„, respectively, are fully suppressed as shown in the figures. RF TO DC CONVERSION EFFICIENCY OF BRIDGE TYPE RECTIFYING CIRCUIT A bridge type rectifying circuit of the rectenna element is shown in Fig. 9 where 1SS154 (Toshiba Si Schottky) diodes are used. The rectifying circuit includes a DC-blocking condenser for the RF side and a bypass condenser for the DC side. The experimental result of the RF to DC conversion efficiency is shown in Fig. 10. The max efficiency of 63% is obtained when the load resistance is 200 ohms and RF inpul power 760 mW. Squares in Fig. 10 are the results obtained by computer simulation. Fig. 3. Radiation characteristic of CMSA.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==