SPACE SOLAR POWER REVIEW Volume 5, Number 4,1985 List of Contents and Author Index Volume 5, 1985
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 Dr. William C. Brown Raytheon Company Colonel Gerald P. Carr University of Texas Dr. David Criswell California Space Institute Mr. Hubert P. Davis Raytheon Company Mr. Gerald W. Driggers, President Combustion Engineering Mr. Arthur M. Dula Attorney: Houston, Texas Mr. I.V. Franklin British Aerospace, Dynamics Group Professor Norman E. Gary University of California, Davis Dr. Peter E. Glaser Arthur D. Little, Inc. Dr. Arthur Kantrowitz Dartmouth College Mr. Richard L. Kline Grumman Aerospace Corporation Dr. Klaus Schroeder Rockwell International Professor Harlan J. Smith University of Texas Mr. Gordon R. Woodcock Boeing Aerospace Company Editorial Assistant: Katie Leydorf Editorial Office: John W. Freeman, Editor-in-Chief, Space Solar Power Research Program, Rice University, P.O. Box 1892, Houston, TX 77251, USA. Publishing, Subscription and Advertising Offices: Pergamon Journals, Inc., Fairview Park, Elmsford, New York 10523, USA; and Pergamon Journals Ltd., Headington Hill Hall, Oxford 0X3 OBW, England. Published Quarterly (ISSN 0191 -9067). Annual subscription rate (Vol. 6,1986) $140.00; Two-year rate (1986/87) $266.00; Special individual rate for individuals whose institution subscribes (1986) $40.00. Members of the SUNSAT Energy Council receive the journal as part of their dues. Note to subscribers: Volume 5 has been carried forward to 1985. Prices include postage and insurance. Microform Subscriptions: Information available upon request. Prices include postage and insurance. Notify 8 weeks in advance of address changes with a copy of the subscription mailing label. Copyright © 1985 SUNSAT Energy Council Copyright Notice: It is a condition of publication that manuscripts submitted to this journal have not been published and will not be simultaneously submitted or published elsewhere. By submitting a manuscript, the authors agree that the copyright for their article is transferred to the publisher, if and when the article is accepted for publication. The copyright covers the exclusive rights to reproduce and distribute the article, including reprints, photographic reproductions, microform or any other reproductions of similar nature and translations. No part of this publication may be 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 copyright holder. Photocopying Information for users In the U.S.A.: The Item-Fee Code for this publication indicates that authorization to photocopy items for internal or personal use is granted by the copyright holder for libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service provided the stated fee for copying beyond that permitted by Section 107 or 108 of the United States Copyright Law is paid. The appropriate remittance of $3.00 per copy per article is paid directly to the Copyright Clearance Center Inc., 27 Congress Street, Salem, MA 01970. Permission for other use. The copyright owner’s consent does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific written permission must be obtained from the publisher for such copying. Please contact the Subsidiary Rights Manager, Publishing Services Dept, at either Pergamon Journals Ltd. or Pergamon Journals Inc. The Item-Fee Code for this publication Is: 0191-9067 /85 $3.00 + .00
INTRODUCTION The Fourth ISAS (Institute of Space and Astronautical Science) Space Energy Symposium was held on 12 February 1985. Twenty-one papers were presented on the subjects of electrical power for spacecraft, energy experiments on board the space station and solar power satellites. These subjects are the same as for the previous symposium, whose proceedings were published as a special issue of the Space Solar Power Review.* For this symposium, the ISAS published just abstracts of papers, and the speakers were encouraged to contribute their papers to the Space Solar Power Review. As a result, eight papers have been submitted and included in this issue. The formality and language peculiar to publication may be a reason why the paper number is fewer than that of the presentations, since the meeting was held in a rather casual atmosphere. As for the special issue for the previous symposium, Professor Freeman, who had invited us to write the papers, took trouble to read all the manuscripts to correct the English. Representing all of the authors, I would like to express our appreciations to Professor Freeman. A special feature of this meeting was the study of the economic aspects of large- scale space power systems, which were discussed for the first time in this symposium. Fortunately the papers are included here. On the other hand, some authors reserved publication intending to refine their concepts for presentation at such overseas conferences as the Congress of International Astronautical Federation. I hope also that they will appear in a future issue of the Space Solar Power Review. For readers who have an interest in the roots of such future articles, a bilingual abstract (in Japanese and English) can be obtained by writing to me: Professor Makoto Nagatomo Space Power System Section Institute of Space and Astronautical Science 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan ★Space Solar Power Review, Vol. 5 No. 2, 1985.
AN APPLICATION OF THE AVAILABLE ENERGY CONCEPT TO THE ECONOMIC EVALUATION OF SPS* M. NAKAGAWA Hitotsubashi University 2-1 Naka Kunitachi-shi Tokyo 186, Japan From the viewpoint of macroengineering with the objective of making a comprehensive strategy for the preservation and improvement of the Earth’s environment through the creation of space civilization foundation, the solar power satellite (SPS) program has the importance of strategic highlands. In the initial phase of creative activities in space, the necessary energy will be self-supplied by means of solar power generation within each individual system. As the size of the activities expands, demands will increase for electric power supply by means of microwave or laser from an independent power center. The system for energy self-supply within space (System a) and the system for energy supply from space to the Earth (System /J) will require different criteria for measurement of economic value. It is assumed that the criteria for the evaluation of economic activities on Earth dictates higher priority of industrialization to a project with better cost benefit as indicated by cost-benefit analysis. Therefore satellite utilization projects which yield more public benefit, such as communication satellite, broadcasting satellite and Earth observation satellite are preferred, and in their industrial applications, the size which meets the principle of profit maximization according to the classic law of cost is selected. The industrial applications of the Space Shuttle for new medicines and new materials are already evaluated to be capable of achieving benefits exceeding break-even points. If we now divide the process of building SPS strategic highlands into phases, Phase A would be achieving the technical and economic viability of the solar power center. That is to say, to set up Central SPS (abbreviated as CSPS) in the center of System a for the supply of electric power to the satellites and the station in the system. (In case surplus power in the system is stored for making CSPS, this may be called Prephase A.) CSPS is operated and managed so as to maintain some reserve after a certain period of time, having met all the demands for System a. Then the phase moves to B for building System ft. CSPS starts transmitting electricity directly to the Earth. It must be noted, however, that System is still at this stage (a subsystem of System a), and is not yet independent. In other words, the total revenue of System a is included in the captial account, and System becomes a special corporation like Electric Power Development Company of Japan. It is a kind *Presented at the Fourth ISAS Space Energy Symposium, at ISAS, Tokyo, 1 March 1985.
of mixed, semiprivate and semipublic company, which can perform even projects below a break-even point, as it can take advantage of the government-industry cooperation. Company (3 supplies electricity from CSPS at the same rates as those on Earth. The sales are to start at the price asked for on Earth. As it is still at the stage of public service, the revenue of surplus-making Division a is used to support the service activities of deficit-making Division /3, as far as the overall business of both a and /3 systems do not become negative in macroaccount. However, any saving of the Earth’s fund for investment in power generation facilities, that results from power supply from space, is accumulated and carried over to the capital account of CSPS special corporation. At a point in Phase C when the internal rate of return of System /3 becomes positive, System /3 is separated from System a in order to reorganize CSPS special corporation into an independent joint stock company. The privatization of NTT (Nippon Telegraph and Telephone Public Corporation) that has recently been accomplished, should be closely observed as a precedent. In this way, Phase D or a space electric power company will reach its golden age. Congratulations! But, one more issue must be considered, namely the criteria for value measurement and evaluation. In particular, how can the input-output analysis of energy within System a be performed? This system produces new medicines, new materials and satellite function services, and sells them to the Earth economy. It purchases economic goods, except land, from the Earth to make those products. For the moment, we can use the conventional econometrics for such input-output analysis. However, the problem is the viability of System a. Here the concept of energy cost and available energy or exergie can be used as a scale for measurement of the viability, in order to obtain evaluation criteria independent of the monetary value system of the Earth economy. These criteria are free from the effects of inflation and exchange rate fluctuations and, as such, they provide an economic evaluation method which eliminates all monetarily converted values, but calculates the cost benefit of resource, energy and products in energy unit (kwh, kcal, etc.) per unit weight.
ON THE INITIATION OF SPS DEVELOPMENT KYOICHI KURIKI Institute of Space and Astronautical Science Komaba Meguro-ku Tokyo 153, Japan Abstract — The concept of finite time availability, a new idea of thermodynamics, is applied to decisions on when the development of the solar power satellite (SPS) should be initiated and how long a lead time should be taken. Admitting the errors in estimation of parameters, an earlier start is concluded to be much safer than a delayed start. INTRODUCTION No phrase can describe more clearly the thermodynamics of finite time availability than “Strike while the iron is hot.” The thermodynamic concept of availability or Gibbs free energy has been frequently applied to economics assessment (1). According to the thermodynamics in equilibrium, the most efficient work can be obtained if the process is quasi-steady. However, the available power tends to zero if the process time becomes indefinitely long and practically the human activities are completed in finite time (2). On the other hand, if the process is too fast, the equilibrium state is totally lost and the available power diminishes, as in the case of a short-circuited battery. The theorem of finite time availability can be precisely applied to macroprojects in deciding the time of their initiation. The solar power satellite (SPS) is an example of macroprojects to be applied. It is apparent that its start in the late 1970s might have been premature considering the technology readiness. In addition, the driverat that lime was the politically-posed energy crisis. In order to prepare for the real crisis in the future, we have to be armed with a methodology for SPS development. The present paper proposes a scheme with reference to the finite time availability. PROCEDURE EOR INITIATION The following is the procedure proposed for the initiation of SPS development. Although the SPS is discussed as the topic in this paper, the following methodology can be generalized. 1. Define the temporal variation of energy costs for terrestrial resources and SPS. *Presented at the Fourth ISAS Space Energy Symposium, al ISAS, Tokyo, 1 March 1985.
Fig. I. Cost curves predicted for terrestrial and SPS energy resources. Find the crossing point of the two cost curves as an ideal time for changing the energy resources from the terrestrial to SPS. 2. Assess the maturity of technologies required to SPS development period e, which corresponds to the relaxation time of finite-time-availability thermodynamics as explained later. 3. Define the start time of SPS development as the ideal time minus e. The details of each step are described in the following. The example of cost curves are shown in Fig. I. The costs of terrestrial resources such as the oil, coal and nuclear are shown to be soaring in the beginning of the next century. Although the coal looks less expensive than the oil, its utilization may be limited by the environmental impacts. Therefore the oil shortage is assumed to occur first in the future as the real crisis. The SPS is considered to take over the resource position of oil. The cost estimation of SPS power contains uncertainty according to the studies in the late 1970s. The error involved is shown as a bandwidth of cost curve in Fig. 1. The cost curve will be revised and its accuracy will be increased as the technology is advanced. The mean value is taken as typical in order to simplify
Fig. 2. Relaxation time e and total cost Ct as functions of lime. Fig. 3. Transition of energy resources from the terrestrial to SPS: (a) earlier start, (b) optimum start and (c) delayed start.
the following discussions. The effect of the error in cost estimation will be discussed in the next section. In contrast to the traditional availability A(/j)-A(/f), the finite time availability tells how much work a system can supply in the transition from state i to state f during the interval r = t} - t, (2). where St is the total entropy production rate. The decrease in the availability repre7 sents the work to be extracted. The system in the present case corresponds to the investment and industry dedicated to SPS construction. The recent finding concerning availability (3) indicates the dissipated availability, - AA, is bounded by the square of L, the length of the shortest path from i to f, multiplied by e/z, i. e. where e is the mean relaxation time of the system and U is the internal energy in equilibrium as a function of multidimensional variable X. The relaxation time, e in our case, is the time required for SPS development. If we include the basic development, the time is a function of readiness of technology including the environmental impact assessment. As the time goes, e decreases to a limiting value as shown in Fig. 2. The expression in Eq. (2) is valid in the quasi-equilibrium case. Whereas in a
nonequilibrium case, such as in extreme urgency, the availability or the distance L is diminished. This effect is taken into account by rewriting L as where n is greater, but not too much greater, than 2. The total cost required for the development of SPS is an increasing function of time Ct as shown in Fig. 2. This is apparent if we estimate the cost in terms of the available energy. From Eqs. (2) and (3) and Ct, altogether, the cost per unit energy required for the SPS development is given by By differentiating Eq. (4) with respect to e/r, t for the minimum specific cost is obtained. The variation of Ct and e during t is ignored; regarded as slowly varying. In the case of n = 2, t0 = e is found. For other/? 2, the factor (//- I)1'" is close to unity, and t0 is approximated by e. The cost of SPS development is charged to energy users as an extra cost and should be reflected in the cost curve in Fig. 1. The curve is revised as shown in Fig. 3. Three curves are shown in this figure: (a) earlier start, (b) optimum start, and (c) delayed start. In the optimum case (b), the start time Tj is so selected that t, = t0 - t or t - e. The time averaged e should be taken for e in Eq. (5) if we approximate its time variation.
It is easy to understand the cases of (a) and (b) in Fig. 3. The earlier start in (a) requires longer lead time e to attain the transition from oil cost curve to SPS curve. The optimum start (b) represents the smoother transition. The delayed start (c) involves three problems. First, the work of construction is supported by using much more expensive energy than in cases (a) and (b). This is reflected in the variation of Ch and the shaded area in Fig. 3(c) is larger than in Fig. 3(b). Second, the basic social activity is supported by more expensive oil energy than SPS energy during /0 tf- This fact imposes an extra charge represented by the hatched triangle region abc in Fig. 3(c). Third, it is very hard to consider the occurrence of a sharp decrease of cost from the point b to c. The natural trend may be a gradual merging from the point b to the SPS curve as represented by the dashed line. If the hatched region in t tf is regarded as extra charge, an enormous long lasting burden is imposed on the energy users. The discussion above relies totally upon well-established cost curves. The inaccuracy of the predicted cost may obscure the transition time to and, hence, the time of initiation. However, since the economic impact is so great in the case of delayed start as demonstrated above, the philosophy of the foregoing discussions will never be blurred by the uncertainties in the prediction. It is apparent in Fig. 3. that the earlier start is much safer than the delayed start. CONCLUSION It is strongly advised that the start time of the SPS development be the earliest possible time of energy resource transition minus the technological relaxation time, REFERENCES I. R.U. Ayers and I. Nair, Thermodynamics and Economics, Phys. Today, 62-71, November, 1984. 2. B. Andresen, P. Salamon, and R.S. Berry, Thermodynamics in Finite Time, Phys. Today, 62-70, * September, 1984. 3. P. Salamon and R.S. Berry, Thermodynamic Length and Dissipated Availability, Phys. Rev. Lett. 51, 1127-1130, 1983.
A SMALL SPACE PLATFORM SYSTEM: POSSIBLE PRECURSOR OF SEEL* M. NAGATOMO, J. ONODA, 1. NAKATANI, K. KURIKI and A. USHIROKAWA Institute of Space and Astronautical Science 4-6-1 Komaba Meguro-ku Tokyo 153, Japan Y. KOBAYASHI University of Tsukuba 1-1-1 Tennodai Sakura Ibaraki 305. Japan Abstract — The Space Flyer Unit (SFU) is a free-flying platform to be carried by the Space Shuttle orbiter. The SFU functions between the experiments on board the platform and the orbiter as a single interface of electrical and mechanical systems. The platform will accommodate experimental instruments in standard payload boxes as well as on the external structure if they are too large to be installed in a box. Experiments in each payload box will be provided with electrical power, telemetry and command service from CDMS of the platform and/or the orbiter or the ground station. An operator on board the orbiter can interact with the experiments via the platform CDMS. The SFU is smaller than the bus platform which is supposed to be used by the Space Energetic and Environmental Laboratory (SEEL), but similar operational capability is expected. Some preliminary experiments for the SEEL will be carried out with a combination of several experimental instruments. For example, the high-voltage solar power test will be used for an electrical propulsion test. Space structure experiment can be applied to the advanced technology development for the SEEL. 1. INTRODUCTION A small space platform, tentatively called the Space Flyer Unit (SFU), was proposed for follow-on missions of the space experiments with particle accelerators (SEPAC), which first flew with the Spacelab Mission One. The SFU is supposed to be an STS payload and can be released from it as a free flyer. This is expected to protect the orbiter from potential hazards caused by electromagnetic phenomena induced by the high-energy particle experiments. The space energetics and environment laboratory (SEEL) is a group of space experiments proposed for a space station mission (1). The SEEL will be carried out with a free-flying bus platform in the later phase of the project. The bus platform is preferred to the main base of the space station by SEEL for the same reason that the SFU was proposed for SEPAC. The SFU is now planned as a multipurpose facility which can be used for space experiments and *Presented at the Fourth ISAS Space Energy Symposium, at ISAS, Tokyo, I March 1985.
observations. In this paper, a preliminary SFU concept will be presented for the purpose of providing information for advanced experiments for the SEEL. 2. DESIGN FEATURES The general features of the SFU will be described well by the design requirements for the platform system. The individual items of the requirements are listed with additional short remarks in the following: Requirement 1: a free-flyer platform to be supported by the NASA Space Transportation System (STS) The SFU will be designed as a payload of the Space Shuttle orbiter to be deployed and retrieved in orbit. The flight period and type of work provided by STS will be determined by each mission. Cost reduction for STS operation will be a design driver. Requirement 2: a general-purpose facility for experiments and observation The SFU will provide experiments with electrical power, thermal control capability, pointing and positioning capability and command and data management for the payload. Any type of payload can be accommodated within the available resources, since it is designed to be a miltipurpose facility. Each mission will be planned by integration of compatible experiments and observations. Requirement 3: a single mechanical and electrical interface between the STS orbiter and on board experiments All the payloads will be fitted to the SFU structure within the limit of the STS cargo bay envelope. Electrical power will be supplied to all payloads by the electrical power subsystem of the SFU. The command and data for the pay load will be managed by the CDMS of the SFU. Requirement 4: simple integration procedures Involvement of the users in the integration work of the SFU payload should be minimized. It is most important to simplify the procedure of assembling the payload and verification of the total system from the standpoint of investigator’s participation. It is considered that the investigators pack the instruments in a unit and bring it to the integration site where work for assembling each package will be performed separately. Requirement 5: easy verification of hardware and software for reflight A conventional space system has been designed for one-time success. The SFU is one of those which will be repeatedly used for several missions. A cost-effective approach to verification of hardware for reflight will be a crucial factor of this system. Selection of materials and structure design is an example of difference of the SFU design requirement from conventional space systems. Requirement 6: future capability Considering that the space station system consists of multiple spacecraft, the SFU is expected to be one of the spacecraft operated under the support of the space
Fig. I. Exploded view of the SFU platform structure. Fig. 2. Typical method of fitting payload on the SFU platform.
Fig. 4. Concept of experimental operation of the SFU platform. cells will be capabale of supplying average total power up to 800 W throughout a mission period. About 60% of the total power can be used by experiments which are contained in the six pay load units. A small amount of energy required for actuators or low-power electronics packages mounted on the external structure will be available from the bus electrical power supply. An experiment requiring more electrical power than this standard has to provide a special power supply as a part of its own equipments. In this case the heat rejection required due to this power consumption is also the responsibility of the experiment. At present, a solar array to generate several kilowatts is being studied for a pay load of the SFU. Control and Data Management The control and data management subsystem (CDMS) of the SFU system is divided into two parts to be located separately in the SFU platform and the Space Shuttle orbiter. The fraction on board the orbiter will be called STS terminal, while the main part of the system on board the SFU platform will be simply called CDMS. Figure 4 shows the general idea of the system operation. The function of the STS terminal is the interface of the SFU system including experiments and the operator. The main data flow from the SFU platform will be passed by the CDMS of the STS to the ground investigators. The STS terminal will pick up necessary data to display them to the operator. If no flight operator is required for a mission, the STS terminal will not be carried in the orbiter, but will be used by the ground operator and experiment investigators. The operators can initialize each experiment and interact with it by changing the parameters used in the software program of CDMS of the SFU platform. A television camera will be installed on the platform to monitor the external configuration, but the image will be updated at an interval of 5 sec or longer.
Navigation and Control According to the preliminary mission study, the requirement for the navigation and control subsystem is featured by two typical cases: a precise attitude control for astronomical observations and a moderate attitude control, capable of determination of position and velocity measurement. The basic capability of the navigation of the SFU platform will be to locate the position and determine the other dynamic characteristics by a hybrid navigation system using an inertial navigation system and the global positioning system. The standard attitude control will be made to satisfy the requirements for the sun-oriented solar array of the electrical power subsystem and the thrust vector control of an electrical propulsion experiment. The actuators for attitude control will be three-axis reaction wheels and reaction control jets. The delta-V capability of the reaction control jets is 20 m/s, which can be used for position control of the SFU platform. If guidance and position control are required, the basic SFU subsystem can support the experiment within such capability. Similarly precise attitude control will be achieved with the basic provision of the navigation and control subsystem by adding star sensors and an electronics package as a part of the experiment. 4. FLIGHT OPERATION The SFU platform will be carried by an STS orbiter to be deployed in a low Earth orbit. After it is released to become a free flyer, the mission will be carried out. After a certain period of free flight, the platform will be retrieved by the STS orbiter or one of later missions. The deployment and retrieval procedure will be the same for every type of mission. The main part of each mission between deployment and retrieval will be different depending on the mission period and extent of the crew participation in the operation and support of data management by the orbiter. The concept of deployment and retrieval operations and each mission mode will be described as follows. Deployment and Retrieval The deployment and retrieval will be performed by the STS crew with the RMS according to a normal procedure specified for the STS operation. Since there is no electrical power supply from the orbiter to the platform, an electrical activation of the SFU system will be made just after it has been taken out from the cargo bay by the RMS. Critical functional tests will be carried out while the platform is held by the RMS. The test data will be checked by the orbiter crew or relayed to the ground for check-out. The last mission operation is to deactivate the SFU platform by a command signal from the STS in operation or the ground operator. Thus the platform will be retrieved at an inactive state as required by the STS operation. Man-Tended Mission Some experiments require the STS to accompany the platform for the purpose of using the orbiter as a remote platform for an optical instrument or reference position in orbit. The orbiter will be controlled to make a formation flight with SFU. Several experiments may be carried out for a mission period as long as a week under the
Fig. 5. Perspective view of array wake with active surface backwards. control of the experiment operators boarding STS. Most of the experiments will be conducted in a semiautomatic sequence. The operator will initialize each experiment and select a required flight mode determined by relative position, attitude mode, etc. The operator can change the time-line of experiments when any trouble occurs. Long-Term Mission There are experiments which do not require an operator. A mission consisting of this type of experiment will be categorized as a long-term mission. When the mission lasts more than the nominal mission period of the STS flight, the platform will be left in orbit to be retrieved by another flight of the STS. Experiments for microgravity material science and astronomical observation would be of this category. 5. GROUND OPERATION There are three phases of the ground operation of the SFU platform, the integration phase, the flight phase and the deintegration phase. Integration Phase A flight mission will include several experiments compatible with each other in terms of the flight operation and resources allocation. After a basic configuration is determined by the project coordinator, the PLU boxes will be delivered to each investigator or developer of the instruments for their work to install the instruments and to verify the function of the assembled unit.
Fig. 6. Relative motion of the SFU platform and the orbiter for high-voltage solar array test. When the final data is collected, the allocation of the PLU boxes to the main structure will be finalized. Then the PLU boxes will be returned to the integrator working with the coordinator to be assembled with the main structure. Interface tests between the experiments and the platform will be conducted with the flight hardware of the STS terminal and ground support equipment which will be used during the flight operation. Then the total system of the platform will be delivered to the STS operator. Flight Phase During the flight phase, the investigators will mostly stay on the ground, participating in a ground operation team. There will be two types of experiments in terms of involvement of payload crew. Some experiments will demand real-time interaction of operator with experimental process, and others will not. For the SFU flight
Fig. 7. A trajectory of simulated motion of the SFU platform during electrical propulsion test. operation, each experiment will be categorized into either of these types. For an experiment which is considered to require real-time interaction by the crew, a flight operation procedure will be prepared. In either case, the ground investigators cannot play an active role in the experiment operation. Deintegration and Refurbishment After a flight, the SFU will be returned to the integration site, where the PLU boxes and instruments mounted on the top will be removed from the main structure. Prior to deintegration of the assembled platform, functional test will be conducted to verify the bus system. The main structure will be inspected for reflight as it is constructed. If necessary, elements of the structure will be replaced by new ones. The PLU boxes containing scientific instruments will be returned to each investigator for postflight check and removal of the instruments. The boxes will be refurbished for delivery to new users. 6. SEEL PRECURSOR MISSIONS Most of the experiments proposed for SEEL are characterized by the high electrical power and heavy instruments, which exceed the capacity of the SFU platform. But an element of an experiment or preliminary test of SEEL can be conducted with the SFU platform, and this is an important step toward the full-fledge test of SEEL. The high-voltage solar array experiment and electrical propulsion test are this kind of experiment. The formation flight operation of the platform propelled by an electrical propulsion and the orbiter will simulate a similar operation of the SEEL bus
Fig. 8. Typical formation flight of the orbiter and the SFU platform for measurement of plasma flow in the geomagnetic field. platform and the space station base. The following is a brief description of these experiments and their operation. High-Voltage Solar Array (HVSA) Experiment The objectives of this experiment are to obtain the mechanical and dynamical characteristics of a solar array and to determine the upper limit of voltage which can be generated by it. The power generated by this instrument will be used for other experiments such as an electrical propulsion test. The solar array will consist of two wings which are 9.6 m x 3.3 m for each. The concerned phenomena of this experiment is electromagnetic interaction of the electrical potential produced on the array surface and the surrounding plasmas as depicted by Fig. 5 (2). This particular experiment will be performed using a single wing to avoid complete loss of the series of missions to use the solar array. The solar cells of the left wing can be connected in orbit to generate various electrical potential distributions. During the test, the effects of not only the environmental plasma but also the turbulence caused by the orbiter will be measured. For this purpose the SFU will make formation flights as shown by Fig. 6 (2). Electrical Propulsion Test Even several kilowatts of electrical power is enough for a study of the effect of exhaust plume of the electrical propulsion on the environment. The thruster of the electrical propulsion will be modularized to be installed in a PLU box with a special thermal radiator to emit the waste heat. A diagnostic package for plasma measurements will be mounted on the main structure of the platform. The primary objective of this test is to evaluate the performance and to measure the exhaust gas flow. Because of constraints of the power supply from the HVSA and attitude control of the SFU platform, the thruster can be fired only when the
thrust vector coincides with the orbital motion and solar cells generate the normal power. Orbital Operation The orbital operation of the SFU platform is different from that of the SEEL because of difference in the orbital altitude. The altitude difference affects atmospheric density and plasma conditions. At the altitude of the space station and SEEL, the deceleration due to air drag is typically as low as 10~6g. It is a concern that the air drag is large compared with the acceleration by the electrical propulsion at the altitude where the SFU platform can be deployed. Figure 7 shows an example of a trajectory of motion of the SFU platform at an altitude of 400 km (2). The trajectory is drawn on the orbital plane. The vertical axis is the local vertical, and the horizontal axis is the direction of orbital motion. The origin of the coordinate is fixed to a drag-free object representing the orbiter. The figure shows that the SFU platform leaves the orbiter being accelerated by electrical propulsion and goes upward and behind the orbiter. When electrical propulsion can work, the SFU platform is decelerated to come back to the orbiter. For a plasma experiment, the phenomena of interest will occur more strongly at the lower altitude, because the plasma density is higher. To study magnetized plasma, the alignment of the orbiter and the SFU platform is required to obtain a certain angle relative to the geomagnetic field line, as shown by Fig. 8 (2). Such a maneuver can be made by the STS orbiter more easily than in the case of a space station. 7. CONCLUSION The SFU is a universal type of space platform which is carried to and deployed in orbit by the STS orbiter. Since the platform is designed to be used for various purposes, the resources of the SFU such as power supply and heat rejection capability are not sufficient for those experiments for the SEEL (space energetics and environment laboratory). However, additional resources can be carried as a payload of the platform. If a high-voltage solar array is carried as an experiment item to be tested, the electrical power can be used for electrical propulsion. The STS orbiter will play a similar role to that of the space station in the case of SEEL operation. REFERENCES 1. K. Kuriki, M. Nagatomo and T. Obayashi, Space Energetics and Environment Laboratory, Space Solar Power Review 5(2), 1985. 2. Small Space Platform Working Group of ISAS and Space Station Task Team, Advanced Technology Experiment on board Space Flyer Unit (SFU), MS-SS-0376-02, Institute of Space and Astronautical Science (ISAS), March f985.
FUNDAMENTAL STUDY ON POWER TRANSMISSION USING LASER BEAMS — DIRECT ENERGY CONVERTER FROM LASER ENERGY TO ELECTRICITY* CHOBEI YAMABE, TOSHIHIKO NAKAMURA, HIROYUKI ISHIHARA, SHIGEYUKI TAKAGI, HIDENORI AKIYAMA and KENJI HORII Department of Electrical Engineering Nagoya University Furo-cho Chikusa-ku Nagoya 464, Japan Abstract — A method of power transmission using a laser beam for a very long distance is proposed here- The characteristics of this method are described, and only the direct energy converter from laser energy to electricity is studied in this work. It is found that the converter energy increases with the magnetic field when the laser-produced plasma is confined by the surface magnetic field. 1. INTRODUCTION It has been proposed (5) to use a laser beam for energy transmission over an ultralong distance from a developing country which is rich in natural energy to a consuming city where there is need for large amounts of energy, or from a solar power satellite (SPS) to the Earth or between space stations. On the other hand, power transmission by a microwave beam has been proposed by Glaser (4). However, the demerits of a microwave beam are longer wavelengths and therefore the necessity of very large equipment because of the large beam divergence and the low energy transmission density due to the air breakdown by the electric field of the microwave. Not many studies on the power transmission using laser beams have been reported. The wavelength of laser light is shorter than that of a microwave beam, and the electric field for the air breakdown with laser light is higher compared to that of the microwave, therefore, the transmission energy density can be increased. Since the conversion efficiency with a laser beam is inferior to that of a microwave beam, for which the method is supported by an established technique, it is important to improve the laser device in efficiency and output power at the region of wavelength which is called “the window of the atmosphere.” It is also important to develop a high-efficiency direct energy converter from laser energy to electricity. In this paper, the direct energy converter from laser energy to electricity with laser-produced plasma is reported. A TEA CO2 laser (wavelength X = 10.6 /xm) is used and its output beam is irradiated on a solid target to produce the plasma. The energy of the initially produced plasma is changed to the expansion energy with the *Presented at the Fourth ISAS Space Energy Symposium, at ISAS, Tokyo, I March 1985.
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polyethylene or carbon target to produce plasma, and the laser energy is transferred to the expansion energy of plasma. After the ions and electrons included in the expansion plasma are separated electrostatically, only the ions are captured on the collector and current flows. The following three processes in the PDC are considered. 3.1 Laser Energy Absorption by Plasma The interaction phenomena of the laser light with the target plasma is different with the laser power density on the target when the laser energy is transferred to the expansion energy of plasma. In the case of the CO2 laser, the absorption mechanism is mainly the classical absorption (inversebremsstrahlung) at less than 1010 w/cm2. Nonlinear phenomena, such as parametric instability and resonance absorption, appear at higher than 1010 w/cm2, and the laser energy is absorbed abnormally by
Fig. 3. The part of the direct conversion and the potential vs. position. Fig. 4. The experimental apparatus.
plasma (9). The former case (< 1010 w/cm2) is considered here. The reflection coefficient R of the laser light claculated from the inversebremsstrahlung is given by the following equation (2). where Z,HL,K and Te are average ion charge number, scale height of the density gradient (~r/2, r is the laser spot radius and equals about 150 gm), wavelength and the electron temperature, respectively. A is also given by the following equation. where Xe and ne are Debye length and electron density, respectively. The measurement of the reflection coefficient using a TEA CO2 laser which is irradiated on the carbon target has been taken (2). According to these results, the experimental values (/?<0.1) are in good agreement with the value given by Eq. (1) at less than 1010 w/cm2, but it is pointed out that the consideration of nonlinear phenomena should be made to explain the experimental results at larger than 1011 w/cm2. In the PDC it is not necessary to make the plasma with high temperature (i.e., several keV) and high density (1022-1025 cm-3) such as can be produced by laser fusion, but it is important to convert the laser energy to electricity with high efficiency. 3.2 Conversion from Kinetic Energy to Expansion Energy While the laser light is irradiated on the target and just after the irradiation, the produced plasma is of relatively high temperature and high density. The electron temperature Te is nearly equal to the ion temperature T, because collisions are dominant in this condition. During the expansion, the kinetic energy of the high temperature and density plasma is converted mainly to the expansion energy, which directs in one direction and becomes the low temperature and density plasma (7). In this case, the distribution function of the expansion plasma/(v) is given by the following equation. Where, w is the expanding velocity, v, M, T. andA are the thermal velocity, ion mass, ion temperature and the Boltzmann constant, respectively. Tonon et al. (13) have obtained the values of I, ~ 30 eV and u ~ 1.4 x 107 cm/s using a TEA CO2 laser. If the value of u is shown by the equivalent expansion temperature Tu, Tu~ 1.4 keV and ~ 0.02. The velocity distribution v is regarded approximately as the 6 function on the scale of u. 3.3 Conversion from Expansion Energy of the Ions to Electricity As the expansion energy of the electrons is smaller by the mass ratio than that of the ions, it is thought best to convert the expansion energy of the ions to electricity after the separation of the ions and electrons. Although both the electrostatic and magnetic separations are considered to separate the electrons and ions, only the former case is reported here. As shown in Fig. 3, the part of the direct conversion is
Fig. 5. The photograph of the magnetic coil. Fig. 6. The electgromagnetic flux (upper) and flux density (lower).
composed of two mesh electrodes and one ion collector. The earthed grid is used so that the electric field of the electrostatic separation does not influence the plasma expansion, and the suppressor grid with negative potential repels the electrons. The ions which pass through the suppressor grid are collected by the ion collector and the collector output voltage is nearly equal to the voltage which corresponds to the expansion energy Tu (eV). The collector current is given by the value of tiieuS taken out as an electrical energy, where nb e and 5 are the ion density arriving at the collector, charge and the collector area, respectively. The conversion efficiency of the PDC is given by the following equation. where The value of depends on the geometrical transmittance of the suppressor grid, the reflected ions by the potential Vrand the secondary electrons from the mesh grid. On the other hand, the value of lc depends on the geometrical transmittance and the secondary electrons from the suppressor grid. It is necessary that the width of the mesh window is nearly equal to the Debye length kD( = 740 V 7(eV)//?(cm 3) (cm), 7 and n are the electron temperature and the electron density, respectively) to separate the electrons and ions effectively. Although the Debye length becomes short in the high density plasma and the mesh interval becomes small, the geometrical transmittance of the mesh cannot be increased due to the heatresisting problem. The electron density n should be decreased by making the expansion area of the plasma large, but in this case, the converter tends to be large in size. For the above reason, the mesh which is strong against the sputtering, heating and high geometrical transmittance with short interval should be developed in future. 4. EXPERIMENTAL APPARATUS The experimental apparatus for generating the electricity using the produced plasma confined by the surface magnetic field is shown in Fig. 4. The output energy of the TEA CO2 laser (10) is 2-4 J/pulse and the full width at half maximum (FWHM) of it is 100-200 ns. A germanium lens with the focal length of 40 cm is used to focus the laser beam. The pressure of the vacuum chamber is about IO-6 torr and the cross-linked polyethylene is used as a target. The magnetic coil shown in Fig. 5 is installed inside along the vacuum chamber and it is divided by twenty-four pairs with two layers and distributed cylindrically. The inner and outer diameters of the coil are 12 cm and 20 cm respectively, and the magnetic wall of 4 cm width is made when the current flows in the coil as shown in Fig. 6. The length of the coil for the axial direction (Z-direction) is 56 cm. The gradient dR/dZ and the decreasing inner diameter of the coil are 0.25 and 6 cm at both ends respectively, where, R is the radial
Fig. 7. The output from PDC as a function of time for without (a) and with (b) magnetic field. Fig. 8. The dependence of magnetic field of the converter output.
position. The current in the magnetic coil builds up to maximum at about 0.8 ms and decreases to 1/e at 2 ms. The laser is synchronized to irradiate the target with the maximum of the magnetic field. The receiving diameter of the PDC is 4 cm and its grid has about 40% transmittance with 400 meshes per inch. The resistance of 1 kfl is used as a collector load. As the shape of the magnetic coil is desired to be conical because the expansion plasma is forced to have one direction (i.e., normal to the PDC) after reflection at the magnetic wall. The distance between the PDC and the target is set at 30 cm to avoid the influence of the end of the coil. 5. EXPERIMENTAL RESULTS The output waveforms of the PDC are shown in Figs. 7(a) and 7(b) for both cases without and with magnetic field. The peak of the output voltage increases and the duration of the waveform is also longer with the magnetic field. In the case of no magnetic field, it seems that a large part of the produced plasma runs away to the R-direction and the ions cannot be collected by the collector. But, on the contrary, with magnetic field, the plasma is reflected at the magnetic wall and some of them are introduced to the collector. The dependence of magnetic field of the converter output is shown in Fig. 8. The converter output with the magnetic current of lb ~ 1150 A (this corresponds to B ~ 0.08 T is about thirty times larger than that of lb=Q. When the converter whose effective diameter is increased from 4 to 22 cm is set at 50 cm in front of the target, the output of the converter of about 2x 10 4 J(~8.2 W) has been obtained at Vc ~ 50 V. In this case, the conversion efficiency of the PDC is about 0.07%. As the conversion efficiency is too small, a multistage Venetian blind direct energy converter (1) has to be used considering the spread of the energy distribution of the incident ions. The detailed experimental results of the parameters of the produced plasma, its behavior and the output characteristics of the PDC will be reported in other papers (6,12). As the efficiency of the electrostatic separation is not good in the high density plasma, the expansion distance of the plasma has to be made long and the plasma density must be low enough to separate the ions from the electrons effectively. (1) The converter output increases up to about thirty times by surface magnetic confinement. But, in this case, the energy for the generation of the magentic field is very large compared with the converter output, and so the total efficiency decreases. Surface magnetic confinement is expected to be used in the large- scale device in the future. (2) When the effective diameter of the converter is increased from 4 to 22 cm, the converter output increases up to about 1300 times without the magnetic confinement. CONCLUSION The characteristics of power transmission using a laser beam has been described, and a fundamental study in which we have turned our attention to only the direct energy converter from laster energy to electricity has been done. The obtained results are as follows.
(3) It is advisable for the PDC that it be hemispherical to increase the efficiency of collection of the produced plasma. REFERENCES 1. W.L. Barrand R.W. Moir, Nuclear Technology/Fusion, 3, 98, 1983. 2. P.E. Dyer, D.J. James, S.A. Ramsden and M.A. Skipper, Phys. Lett 48A, 311, 1974. 3. T. Fujioka, A. Nogucki, A. Sano, T. Uchiyama and M. Obara, Reports of Special Project Research on Energy, p. 203. November 1983 (unpublished). 4. P.E. Glaser, U.S. Patent 3781, 647, 1973. 5. K. Horii, Researches Report of Electrotechnical Laboratory Headquarters, 36, 279, 1972 (in Japanese, unpublished). 6. H. Ishihara, T. Nakamura, H. Akiyama, C. Yamabe and K. Horii, Rev. Laser Eng. (to be submitted). 7. D.W. Koopman, Phys. Fluids, 14, 1707, 1971. 8. K. Kuriki and K. Akai, XXXI Congress International Astronautical Federation IAF-80-A-20, Tokyo, 1980. 9. K. Niu and H. Sugiura, Nuclear Fusion (in Japanese), Kyoritu-Syuppan, pp. 84-95, 1979. 10. S. Sato, C. Yamabe and K. Horii, IEE Japan 100A, 657, 1980. ILA. Sona, Laser and their Application, p. 349, Gordon and Breach, New York, 1976. 12. S. Takagi, H. Ishihara, H. Akiyama, C. Yamabe and K. Horii, Kakuyugo-Kenkyu 50, 719, 1983 (unpublished), and Jpn J. Appl. Phys, (to be submitted). 13. G. Tonon and M. Rabeau, Plasma Physics 15, 871, 1973.
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