SPACE SOLAR POWER REVIEW Volume 1, Number 4, 1980 PERGAMON PRESS • New York/Oxford/Toronto/Paris/Frankfurt/Sydney
SPACE SOLAR POWER REVIEW Published under the auspices of the SUNSAT Energy Council Editor-in-Chief Dr. John Freeman Space Solar Power Research Program Rice University, P.O. Box 1892 Houston, TX 77001, USA Associate Editors Colonel Gerald P. Carr Bovay Engineers, Inc. Dr. M. Claverie Centre National de La Recherche Scientifique Dr. David Criswell California Space Institute Mr. Leonard David PRC Energy Analysis Company Mr. Hubert P. Davis Eagle Engineering Professor Alex J. Dessler Rice University Mr. Gerald W. Driggers L-5 Society Mr. Arthur M. Dula Attorney; Houston, Texas Professor Arthur A. Few Rice University Mr. I.V. Franklin British Aerospace, Dynamics Group Dr. Owen K. Garriott National Aeronautics and Space Administration Professor Norman E. Gary University of California, Davis Dr. Peter E. Glaser Arthur D. Little Inc. Professor Chad Gordon Rice University Dean William E. Gordon Rice University Dr. Arthur Kantrowitz Dartmouth College Mr. Richard L. Kline Grumman Aerospace Corporation Dr. Harold Liemohn Boeing Aerospace Company Dr. James W. Moyer Southern California Edison Company Professor Gerard K. O’Neill Princeton University Dr. Eckehard F. Schmidt AEG—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: Betsy Julian Editorial Office: John W. Freeman, Editor-in-Chief, Space Solar Power Research Program, Rice University, P.O. Box 1892, Houston, TX 77001, USA. Publishing, Subscription and Advertising Offices: Pergamon Press, Inc., Fairview Park, Elmsford, New York 10523, USA; and Pergamon Press Ltd., Headington Hill Hall, Oxford 0X3 OBW, England. Published Quarterly. (ISSN 019I-9067) Annual subscription rate (1981) $65.00; Two-year rate (1981/82) $123.50. Special reduced rate for individuals whose institution subscribes $30.00. (Members of the SUNSAT council receive the journal as part of their dues.) Prices include surface postage and insurance; air mail subscriptions extra. Microform Subscriptions: Simultaneous subscriptions on microfiche and microfilm supplied at the end of the volume with index are available from: Pergamon Press and/or its division, Microforms International Marketing Company, Fairview Park, Elmsford, New York 10523 USA; and Headington Hill Hall, Oxford OX3 OBW, England. Copyright © 1980 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. U.S. Copyright Law applicable to users in the U.S.A.: The Article Fee Code on the first page of an article in this journal indicates the copyright owner's consent that in the U.S.A, copies may be made for personal or internal use 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 should be forwarded with a copy of the first page of the article to the Copyright Clearance Center Inc., 21 Congress Street, Salem, MA 01970. If a code does not appear copies of the article may be made without charge, provided permission is obtained from the publisher. 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. In case of doubt please contact your nearest Pergamon office. Cover photo representation of SPS Courtesy NASA.
0191 -9067/80/040263-01502.00/0 Copyright c 1980 SUNS AT Energy Council EDITORIAL When asked by OMNI magazine (August, 1980) whether he supports the proposal for Solar Power Satellites, Dennis Hayes, Director of SERI, replied as follows: SERI is not doing any work directly related to that, and so I am not deeply knowledgeable about it. My personal reading of practical politics today is that it’s going to be very difficult to pursue any energy option that requires an expenditure of eighty billion dollars before you get anything out of it. Moreover, even if the optimistic projections for the cost of power from such satellites proves accurate — and this is very far from being assured — I think we can meet the same cost goals with fewer risks by using terrestrial solar technologies. This statement probably accurately reflects the attitude of many in Washington and sums up neatly SPS’s credibility problem. It would seem that this problem can only be countered by a twofold approach. First, a new thrust must be established to reduce SPS front-end costs, possibly with modular designs that allow a start with smaller satellites which are “on-line” systems but which are expandable to higher power later on. The problem with the smaller systems, of course, is lower efficiency, but have we become entrapped by a “5 GW” mentality to the point where our thinking is too constrained? The reference system had a purpose. It has served that purpose well. Now we must go on from there. This of course will take more dollars. Second, the question of risk relative to terrestrial solar must be addressed repeatedly in professional reports which are made available to the public. It is not sufficient to simply assert that terrestrial and space solar are complimentary rather than competitive. Rather, the advantages and disadvantages, e.g., energy costs, etc., roles and function of each must continue to be thoroughly and honestly explored, and the results discussed openly in a public forum such as the SPACE SOLAR POWER REVIEW. These issues are, of course, being addressed in the DOE program, but the work is far from complete and what work has been done has not reached all the players. Let’s have more papers. JOHN W. FREEMAN Editor-in-Chief
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0191 -9067/80/040265-03$02.00/0 Copyright ® 1980 SUNSAT Energy Council LETTERS TO THE EDITOR To the Editor: The recent SPS conference explored numerous configurations and design concepts for solar power satellites. One concept which was not addressed and which may turn out to have a major impact on system feasibility is the use of a single space antenna transmitting to multiple receivers. Conceptually, this is similar to the capability of phased array radar to focus beams on several targets simultaneously. Although several distinct transmitting arrays could be placed on a satellite, transmitting multiple beams from a single array should allow a simpler structure, greater operational flexibility, and quite possible a larger effective aperture than would be the case if multiple antennas are used. There are certain constraints; the individual phase-controlled elements must have a relatively low gain so that the beam can be steered over a reasonable angle (several degrees) by phasing. This would seem easier in a solid-state concept with individually excited elements than in a klystron concept with large high-gain subarrays. Second, the simultaneous transmission of multiple beams from a single array creates interference patterns across the array — some transmitting elements are more heavily loaded than others. Provided the various beams are transmitted on slightly different frequencies, however, the interference fringes will move radpily across the array, and mean power levels will be uniform. Thermal overload should therefore not be a problem, although peak power levels would be higher. How would such an approach impact the system? Since increasing the size of the transmitting array would allow many rectennas to be reduced in size, the optimal spacetenna might be larger and the optimal rectenna much smaller. The optimal power output of the satellite would be increased since its output would be marketed to several areas. When additional power is needed, it might well be more cost- effective to increase the size of the solar and microwave arrays of an existing satellite than to build another SPS. Similar considerations might apply to the rectenna — it might be useful for a given rectenna to receive power from several satellites (i.e., to increase rectenna power density without increasing power density in the ionosphere). The problem of thermal overload, at least, would be minimized if the beam frequencies were not identical. Daniel Woodard 420 Market St Galveston, TX 77550 (R. H. Dietz of the Johnson Space Center was asked to reply to the above letter. Mr. Dietz’s reply follows.-Editor) To the Editor: Per your request, I have reviewed the letter to you from Daniel Woodard. The
subject of multiple beams was discussed at the SPS Conference in Nebraska at both sessions on Power Transmission in the following papers: I. Power Transmission I — ‘‘Microwave System Performance Summary.” 2. Power Transmission II— ‘‘High-Power Microwave Optics for Flexible Power Transmission Systems.” 3. Power Transmission II — “SPS Power Transmission — Are Multiple Beams a Better Option For Europe?” Dr. Woodard is generally correct concerning the advantages of the concept. Our studies to date have generated some questions of implementation, however. It may be possible to jitter the RF pattern across the array fast enough to meet the thermal time constants, however, components must still be able to withstand stresses encountered at the combined power levels, and must be able to be amplitude modulated at the jitter frequency. Implementation of a phase control system for multiple beam formation and pointing at one or more rectenna sites presents many unanswered questions. Variation in sidelobe levels with scan and number of beams is an unknown, and will probably require determination by empirical methods. R. H. Dietz SPS Microwave Systems To the Editor: Obviously the enclosed “manuscript” is not exactly within the scope of your SPACE SOLAR POWER REVIEW. Somehow each of us is drawn to space in his or her own individual way and as one moves along through life one contributes in the way that he can. Hence the poem. LIFE AMONG THE STARS Go to Space? No reason is clear Except we must. Time is near. Earth’s great cradle, mysterious and black Calling us forward, calling us back. And what is space, but a stage to play Our gift of living for brief life's stay. To live, life must seek, know and find That strange singularity to satisfy its mind. Forward we go among the stars. Our orb has nurtured human being, and other Stand strong and proud O’ brave mother. The West is gone, what will we do! The moon glimpsed Apollo, but are we through! Let’s accept the challenge, a task not great To refuse, a sadness too hard to take. Gravity’s child arise and see Strike hard, aim high what man can be! To life among the stars.
Idiot’s tale, folly extreme, Life, that Devil within reigns supreme. Driving us out far from home Towards nothing, empty and coldly alone. And Space, black void of treacherous song, Calling forth only our strong. To boldly step from maudlin peer Full of hope and full of fear To live among the stars. Tomorrow people, are you one? To take the step, to be a sun. Outward we’ll go to live in space Earth’s lone seed in foreign place To come down again on the other side To final goal and future ride Bounding on no reason yet For life among the stars. Lawrence J. Driscoll Architect 2 S. 631 Cynthia Drive Warrenville, Illinois 60555
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0191 -9067/80/040269-11 $02.00/0 Copyright ® 1980 SUN SAT Energy Council CHANGES IN THE TERRESTRIAL ATMOSPHERE-IONOSPHERE-MAGNETOSPHERE SYSTEM DUE TO ION PROPULSION FOR SOLAR POWER SATELLITE PLACEMENT S. A. CURTIS and J. M. GREBOWSKY Laboratory for Planetary Atmospheres NASA/Goddard Space Flight Center Abstract — In order to construct Solar Power Satellites using earth-based materials, sections of a satellite must be lilted from low earth to geosynchronous orbit. The most plausible method of accomplishing this task is by means of ion propulsion based on the relatively abundant terrestrial atmospheric component, Ar. The proposed propulsion system will release a dense beam of ~5 keV Ar* (1). The total amount of Ar* injected in transporting the components for each Solar Power Satellite is comparable to the total ion content of the ionosphere-plasmasphere system while the total energy injected is larger than that of this system. We give preliminary estimates of the effects massive Ar* injections have on the ionosphere-plasmasphere system with specific emphasis on potential communications disruptions. The effects stem from direct Ar’ precipitation into the atmosphere and from Ar* beam induced precipitation of MeV radiation belt protons. It is suggested that should more detailed studies find the environmental modifications intolerable, the use of lunar-based rather than earth-based satellite construction materials should be considered. 1. INTRODUCTION We wish to examine the possible environmental impacts of one aspect of Solar Power Satellite (SPS) construction involving the lifting of SPS components from low earth orbit to geosynchronous earth orbit using orbital transfer vehicles powered by solar arrays. In current studies, this is the second stage of a two-step process envisioned when terrestrial materials are used in SPS construction (1). The first step is lifting materials from the earth’s surface to low earth orbit with a heavy lift launch vehicle which is planned to be an enlarged later generation of the current Space Shuttle. In the second step, orbital transfer vehicles will inject ~2 x IO6 kg of ~5 keV argon ions into the near earth environment in the process of carrying the components that will comprise the £10* kg SPS (2) from low earth orbit to geosynchronous earth orbit. The physics of this Ar+ beam has been studied in detail by Curtis and Grebowsky (3). They show that only a small fraction of the total mass of the Ar+ beams emitted by the orbital transfer vehicles is stopped in the plasmasphere. We note that another preliminary study (4) has tentatively concluded that all of the Ar+ beam is stopped in the plasmasphere. However, even if only a fraction of the beam is stopped, this fraction represents a very large injection of energetic ions relative to the naturally occurring plasmasphere plasma. It is this massive release of energetic
Fig. I. Diagram of low earth orbit (LEO) to geosynchronous earth orbit (GEO) orbital transfer. Up times for transfer from LEO to GEO, tup, and from GEO to LEO, tdown are also given. ions in the upper ionosphere, the plasmasphere and the outer magnetosphere that is the subject of this paper. The release is viewed as giving rise to significant man-made perturbations of the earth’s atmosphere, ionosphere and magnetosphere and here long-term disruptions of terrestrial radio wave communications are shown to be plausible. 2. VEHICLE AND ORBIT DESCRIPTION The basis of our investigation is formed by recent studies of orbital operations required for SPS construction (5). These studies indicate that the SPS components will be carried from low earth orbit to geosynchronous earth orbit by about 10 orbital transfer vehicles. Each orbital transfer vehicle will consist of a solar powered array of 300 one megawatt ion thrusters having an area of — 107/cm2. This thruster array will be attached by cables to the partially assembled SPS structure to be moved to geosynchronous earth orbit as shown in Figure 1. The ion thrusters’ fuel is argon due to its relatively high abundance (—1% of total atmosphere) and low cost (1). Additionally, the relatively low first and high second ionization potentials of Ar as well as its high specific impulse and thrust resulting from its intermediate weight also make it a reasonable choice (5). An orbital transfer vehicle will require —130 days for the low earth orbit to geosynchronous transfer. Thus, all of the orbital transfer vehicles will be flying almost simultaneously since the desired building rate of SPS is projected at one per —180 days. The transport of the SPS materials from earth to low earth orbit
TABLE 1 PLASMA PARAMETERS/OTV (ORBITAL TRANSFER VEHICLE) is limited to —50 days and thus a high launch frequency of the heavy launch vehicles is required. The total number of SPSs envisioned to supply a substantial amount of the U.S. electrical power requirements will require construction and transport over a period of decades (6). The transfer orbit from low earth orbit to geosynchronous earth orbit will be a spiral that is most tightly wound at lower altitudes. Hence the orbital transfer vehicles will be spending most of their time near the earth where most of the deposition of the 5 keV Ar+ will occur, tending to maximize environmental effects there. The ion beam emitted by the orbital transfer vehicle will have a transverse velocity spread of -0.4 Vb where Vb = 150 km sec 1 is the beam velocity (2). The beam will therefore spread rapidly during its transit time through the plasmasphere (100-200 sec). Typical plasma parameters for an orbital transfer vehicle are shown in Table 1 (2). 3. ION BEAM DYNAMICS AND ION LIFETIMES IN THE PLASMASPHERE In this section we outline the physics of ion beam dynamics and mass loss in processes controlling the magnetosphere. In addition, the lifetimes of the ions constituting the mass loss are discussed. For more detail with a discussion of the underlying physics we refer the reader to our companion paper (3). The ion beam formed by the exhaust of the cargo orbital transfer vehicle possesses a sheath on its outer surface with a thickness of about a Debye length. Within this sheath the polarization electric field responsible for the cross field transport decreases and hence the sheath ions are slowed and inhibited from traversing the local magnetic field with the bulk of the beam. As a consequence of this sheath effect the ion beam constantly loses beam ions leaving them behind during the beam’s motion through the near earth space environment. Curtis and Grebowsky (3) showed that plasma instabilities are ineffective in stopping the beam in the plasmasphere due to the constraints on plasma wave amplification imposed by the rapid change in the diverging beam density. Further, mass loading of the beam by the ambient plasma as studied by Scholer (7) does not appear capable of slowing the bulk of the beam due to its transalfvenic velocity in some regions of space and due to its supersonic motion everywhere. The total mass loss of the ion beam in the magnetosphere is approximately \%-10%
Fig. 2. Total radial density profile of Arr resulting from a fleet of orbital transfer vehicles transporting materials for one SPS from low earth orbit to geosynchronous earth orbit. of the initial beam mass (3). Given the large beam injection rates suggested by Table 1, the plasmasphere loading per SPS constructed would result in a 1%-10% number density increase and a two order of magnitude increase in energy density when compared to the naturally occurring cold plasma in this region, in Figure 2 we display the total Ar+ beam deposition per SPS as a function of radial distance from the earth's center L. For comparison the typical plasmasphere density is about 103 cm’3. The lifetimes of deposited beam ions were determined for three mam loss processes: charge exchange, electron coulomb scattering, and pilch angle scattering due to turbulence induced by beam ion anisotropy. Within the plasmasphere, electron coulomb scattering represents the fastest loss process y ielding lifetimes of only about one day near low earth orbit. Near the plasmaspause, however, the lifetime could be montns. Since electron coulomb scattering is sensitive to ambient temperature, if the deposited beam ions give rise to substantial plasmasphere heating then charge exchange could be the dominant loss process below altitudes of about 6000 km. Plasma instabilities driven by the anisotropic Ar+ may give rise to intense turbulence. This turbulence could in turn scatter Ar+ into the atmospheric loss cones where the ions precipitate out. The significance of this effect is determined by how far above the limiting flux level the deposited Ar' ions are. Further research is required to better quantify the expected turbulence levels. The turbulence is very difficult to simulate theoretically and active experiments in space to obtain a final answer as to the magnitude of its effects may be required.
Beyond the plasmapause, the dominant loss mechanism is charge exchange with pitch angle scattering by plasma turbulence again playing a significant role. Convective fields which will drive the drift motion of the Ar1 ions in the outer magnetosphere may also contribute significantly to the loss rates (8). 4. POSSIBLE ENVIRONMENTAL IMPACT: COMMUNICATIONS A. Communications Effects Due to Plasmasphere Perturbations From our discussion of beam propagation through the plasmaspnere and the resulting deposition of energetic ArT in substantial quantities over distances of several earth radii and with lifetimes of up to a year, we see that substantial changes may be expected in the near earth plasma environment. In this section we deal specifically with possible effects on terrestrial communications of the enhanced precipitation of energetic ions induced by the 5 keV Ar' beam. It is well known that enhanced precipitation of energetic particles occurring during solar Hares can seriously disrupt communications links (9, 10, 11). Fortunately, these naturally occurring disruptions are of relatively short duration (~ days). However, in the scenario which we present here, there is the potential for communications disruptions over periods of decades as a consequence of the continuous construction of an SPS fleet. Due to their initial injection almost perpendicular to the local ambient magnetic field the deposited energetic Ar+ possess a high level of pitch angle anisotropy. This pitch angle anisotropy provides free energy which drives plasma instabilities and hence plasma turbulence. In addition to the plasma turbulence driven by the energetic Ar4 deposited by the beam, short duration turbuience is also generated by the beam itself as it propagates outward through the plasmasphere. Instabilities expected in this case include the beam-plasma instability driven by the beam’s high velocity, drift wave instabilities driven by the density gradient of Ar’ at the beam’s surface, and the Kelvin-Helmholtz instability driven by the velocity gradient near the beam’s surface resulting from the nonuniformity of the polarization electric field. Due to the beam’s short residence time (100-200 sec) in the plasmasphere the effects of these plasma instabilities on the beam’s attenuation will most likely be minor (3). The plasma turbulence will tend to both isotropize Ar as well as the various naturally occurring components of the plasmasphere population. In particular the radiation belt ions will be affected. These ions, mostly protons, are characterized by high energies and fluxes. For energies E ~ 50 MeV, fluxes greater than IO4 cm 2sec 1 are encountered between/. = 1.2 andL = 1.8 and forE> 0.4 MeV, fluxes above 105 cm2sec 1 exist beyond L = 2.0 (12). The high fluxes of high energy protons exist precisely in the region off s 2.0 where most of the Ar4 deposition occurs as shown in Figure 2. Since the turbulence level will be proportional to the number density of Ar+, precipitation effects may be substantial in the inner radiation belt. A specific instability which could give rise to turbulence that could scatter the radiation belt protons into their loss cones is the electromagnetic ion cyclotron instability. This instability would be driven by Arf anisotropy. The electromagnetic ion cyclotron mode as discussed in the literature (13,14) characteristically displays a multiple harmonic spectrum. The fundamental harmonic is the gyrofrequency of the energetic ions which drive the instability. Such spectra have been observed in the earth’s plasmasphere (15) with many harmonic lines extending up to the vicinity of
Fig. 3. Values of L mapped from the earth’s equatorial plane to a 100 km altitude (16). one half of the lower hybrid frequency even for heavy ions. Thus, the waves may have frequencies m ~ m Qi, m > 1. The characteristic wavelengths have kp„ > 1 where k is the wave vector and p„ is the gyroradius of the plasmasphere protons. For resonant wave particle interaction we require (14) where v is the radiation belt proton velocity, vh the radiation belt proton velocity component along the local magnetic field, is proton gyrofrequency and n is an integer, and since m ~ m there exists large enough m such that m = n and the resonance condition can be satisfied by the small doppler shifts and relativistic effects indicated. We thus would expect a resonant interaction between the Ar+ driven turbulence and the radiation belt protons. The magnitude of these interactions and effects require additional study to better estimate them. The precipitating protons will have energies up to —100 MeV and hence may be expected to have effects similar to those of solar flares. Although solar flare protons precipitate mainly at high latitudes while the Ar+ turbulence scattered energetic radiation belt protons precipitate at low to mid-latitudes, their effects on ionizing the atmosphere are much the same. This is the case since the recombination times which control the lifetime of the plasma created by the energetic proton precipitation has only a weak latitudinal dependence (A. Aikin, verbal communication). The resulting
spatially irregular plasma created then has roughly the same lifetime for either source and the effects on radio waves may be expected to be similar, although at different geographical locations. In Figure 3, we show a map of the western hemisphere with the near surface L values projected from the earth's equatorial plane (16). Since precipitation is expected between L = 1.1 low earth orbit and L~ 4.0 (plasmapause), most of effects will occur over a latitude range which is roughly centered about the continental U.S. In Figures 4a and 4b (17) we show the spatial distribution of energetic radiation belt protons for E > 50 MeV and E > 0.4 MeV which may be precipitated. We may estimate the lifetime of the radiation belt protons in the plasma turbulence generated by the Ar+ using the expressions developed by Curtis and Grebowsky (3). Noting that the bounce times are 0.5 to 1 sec for the MeV energy protons and taking the number of bounce periods required to isotropize the MeV ions as about the same as that of the Ar+, depletion of radiation belt protons can occur up to two orders of magnitude faster than the Ar+. We may then expect substantial fluxes of radiation belt protons to precipitate before the Ar+ turbulence subsides due to the Ar+ population's approach to a limiting flux condition. As the Ar* beam propagates outward during the orbital transfer vehicle’s trip to geosynchronous earth orbit a continuous source of anisotropic Ar+ will exist extending from the orbital transfer vehicle’s orbit to the plasmapause. Thus precipitation effects will extend over the lifetime of the SPS construction (—6 months/station). In addition to the pr.oton precipitation, Ar+ precipitation due to plasma turbulence may be expected as well as the ionization effects due to precipitating —5 keV argon neutral atoms resulting from charge exchange. Also, direct precipitation will occur at orbits near low earth orbit due to the ion beam velocity spread. The penetration depth of the energetic ions will range from stratospheric altitudes for the more energetic radiation belt protons to mesospheric-thermospheric altitudes for the energetic Ar+ and Ar (18). We note that even if only 0.01% of the deposited beam energy is converted to plasma turbulence (19) the expected wide band wave amplitude characterizing this turbulence will be — 10' my which is much greater than the natural wave amplitudes observed closely confined to the earth’s magnetic equatorial plane of —20 my (15). The turbulence amplitudes are less than 1% of the ambient magnetic field. Thus a 3 order of magnitude enhancement of plasma wave turbulence above its natural maximum level may be possible. The stated beam energy to plasma turbulence conversion is meant to be suggestive of the possible effect’s magnitude. The reduction of this number by orders of magnitude would still produce significant effects. We also note that the number used for conversion efficiencies is considerably less than that deduced from observations of plasma instability processes in other papers in the literature (20). The possible high levels of turbulence are consistent with our conclusion that greatly increased ion precipitation may be expected. This expectation is also in agreement with the recent results of the Cameo experiments that involved the release of large quantities of Ba into the magnetosphere (J. P. Heppner, private communication) which may have triggered auroral type particle precipitation. These experiments are known to have produced much greater than normal rf scintillations and signal attenuation as determined from monitoring a pass of the U.S. satellite GEOS-3. This scintillation and attenuation is precisely the type of communication impairment expected from the Ar+ induced precipitation. Ionospheric scintillation will be produced by ionospheric electron density inhomogenities due to the spatial
Fig. 4. Radiation belt proton fluxes for energies (a) E > 50 MeV , (b) E > 0.4 MeV (after NASA SP-8116, 1975).
variation in the precipitating fluxes. The results of these processes will be similar to the conditions experienced during solar flare events with bandspreading and signal fadeout (10) occurring. For another view of SPS induced perturbations in the magnetosphere we refer the reader to the literature (21). The effects of this long-term enhanced precipitation and Ar+ injection on the radiation belts' populations reauires additional research on radiation belt source and sink mechanisms. However, it appears quite possible that radiation belt fluxes due to alterations of both sources and sinks may remain at levels comparable to their present ones. B. Communications Effects Due to Outer Magnetosphere Perturbations Although no beam injection occurs beyond geosynchronous earth orbit some beams will be injected closer to the earth in the magnetotail direction. We note that the beam is injected tangentially to the transfer vehicle’s orbit. In the outer magnetosphere, the beam density > n,. where n,. is the critical density above which the beam is not stopped (3). Thus, some of these beams will propagate through the magnetotail shedding Ar+ due to the gradient in the polarization electric field across their sheath. Again these shed Ar+ ions are anisotropic. This anisotropy provides the free energy source to drive an ion cyclotron instability. The ion cyclotron instability can rise to anomalous resistivity (22.23). For relatively high mass ions such as Ar\ the instability threshold is lower (24) and hence the resistivity may reach a high level before the instability is shut off (19). Naturally occurring O+ ions of ionospheric origin in the tail would require a level of free energy comparable to that of the Ar+ ions in order to be a source of anomalous resistivity. The increase in anomalous resistivity could lead to an increase in the rate of magnetic field line merging (C. S. Wu, private communication). Due to the possible connection between merging and substorms (25), the result could be an increased frequency of magnetospheric substorms with potentially disruptive effects on the high latitude ionosphere and radio communications. An increase in auroral activity could also be expected. As within the plasmasphere, the beam deposited Ar+ will drive instabilities and hence give rise to turbulence. The result of the turbulence could be increased precipitation of ions naturally occurring in the outer magnetosphere shown in Figure 4b. Arf will also be precipitated out of this region. Since L > 4, the precipitation will occur at higher latitudes giving rise to ionization irregularities and therefore radio communication impairment at these higher latitudes. Finally, we note that convective electric fields by their effects on Ar' drift motion, may also play an important role in loss processes in the outer magnetosphere and limit the Ar+ lifetimes (8). 5. SUMMARY AND CONCLUSIONS In the preceding sections we have described possible consequences of one aspect of the construction of a large fleet of solar power stations. The part of the construction process considered was the transport of large quantities of materials with total masses in the range of hundreds of thousands of metric tons from low earth orbit to geosynchronous earth orbit. This orbital transfer procedure would entail the release of millions of kilograms of 5 keV argon ions modifying the near earth plasma en-
vironment and producing potentially serious effects on terrestrial communications. The Ar' deposited in lifting an SPS to geosynchronous earth orbit will have a greater total energy content than the ionosphere-plasmasphere system. However, if these SPS craft were to be built out of lunar materials as envisioned by some authors (26), the possible impacts discussed earlier could be largely avoided since the energy required to transport materials from the lunar surface to geosynchronous earth orbit is much less than hauling materials from low earth orbit to geosynchronous earth orbit. Thus, not only would less propellant be needed but it would be deposited much farther from regions where it may have a direct effect on human terrestrial activity. More specifically, given the large number of SPSs envisioned in order to significantly contribute to U.S. electrical power needs, the economic savings in transporting materials from the lunar surface to geosynchronous earth orbit compared to transport from the earth’s surface to geosynchronous earth orbit apparently more than offsets the probable capitalization cost of setting up lunar factories given current cost estimates (P. Glaser, verbal communication). We note that the terrestrial materials required to set up the lunar factories are small compared to an SPS mass in present studies (26). Since the environmental impacts discussed in our paper scale with the transported mass, the impacts of lunar factory construction on near earth space would be small compared to those due to the transport of one SPS. Lunar factory products could be lifted from the lunar surface to low lunar orbit via mass driver engines (26). From low lunar orbit partially assembled sections of an SPS could be lifted to geosynchronous earth orbit via ion propulsion. The energy expanded in low lunar orbit to geosynchronous earth orbit transport, E (LLO-^GEO) compared to the energy expended in low earth orbit to geosynchronous earth orbit, E (LEO—>GEO) is where Ve and V, are, respectively, the terrestrial and lunar escape velocities; re and r; are the planets’ radii; M,. and M,, the planets' masses; R is the earth-moon distance, and D is the distance from earth to geosynchronous earth orbit. Thus the energy expenditures are greatly reduced and for a given ion beam energy the total number of ions emitted would be reduced by a factor of —20. The greatly reduced amount of Ar required for each SPS placement (S105 kg) could be transported from earth with a small impact compared to earth based SPS transport which require —10* kg be transported per SPS. The number of Ar+ shed by the ion beam would be reduced by more than an order of magnitude. Not only would the number of Ar+ shed be sharply reduced, but the deposition would occur at L > 6.6 well beyond the plasmapause. The radiation belts would then be unaffected and potential low to mid-latitude communication disruptions avoided. Using a lunar based transport system, the reduced Ar+ ion deposition in the outer magnetosphere would only affect precipitation at high latitudes and would be less severe than that due to earth based transport because of the lower energy requirements for transportation. We conclude, on the basis of our preliminary study, that if a fleet of SPSs were to be fabricated, the use of lunar rather than terrestrial materials would appear to minimize the environmental impacts in addition to giving economic benefits derived from transportation cost reduction.
Terrestrial materials would seem to be a viable alternative in the construction of a less than full scale SPS demonstration facility. We emphasize, however, that major strides are required both in our understanding of the physics of the possible environmental effects and of the detailed engineering problems of SPS construction before the choice between terrestrial and extraterrestrial materials can be made. The present need is to keep the option of pursuing both paths open until one can be distinguished as being clearly superior on the basis of very detailed, exhaustive studies. REFERENCES I. G. Hanely and C.H. Guttman, Satellite Power Systems Concept Definition Study: Final Report Executive Summary. Rockwell International, Vol. I, April 1978. 2. G. Hanley and C.H. Guttman. Satellite Power Systems Concept Definition Study: Final Report Transportation and Operations Analysis, Vol. V, April 1978. 3. S.A. Curtis and J.M. Grebowsky, Energetic Ion Beam Magnetosphere Injection and Solar Power Satellite Transport,./. Geophys. Res., 85(1729), 1980. 4. Y.T. Chiu, J.M. Cornwall, J.G. Luhmann and M. Schulz, Argon-Ion Contamination of the Plasmasphere, submitted to Progress in Astronautics and Aeronautics: Space Systems and their Interactions with the Earth’s Space Environment, AIAA, 1979. 5. E. Stuhlinger, Ion Propulsion for Space Flight, McGraw-Hill, Inc., New York, 1964. 6. P.E. Glaser, Solar power from satellites, Physics Today, 30(30), 1977. 7. M. Scholer, On the Motion of Artificial Ion Clouds in the Magnetosphere, Planet. Space Sci.. 18(977), 1970. 8. D.P. Stern. The Electric Field and Global Electrodynamics of the Magnetosphere. Rev. Geophys. Space Phys., 17(626), 1979. 9. P.E. Argo and JR. Hill, Radio propagation and solar cycle 21, in Effect of the Ionosphere on Space and Terrestrial Systems, J.M. Goodman (ed.), U.S. Government Printing Office, 371, 1978. 10. Y.K. Wong, K.C. Yeh and C.H. Liu, Mean arrival time and mean pulse width of signals propagating through an inhomogeneous ionosphere with random irregularities, in Effect of the Ionosphere on Space and Terrestrial Systems. J.M Goodman (ed ), U.S. Government Printing Office, 470, 1978. II. C.W. Prettie, Upper limit to the bandspreading and fade rates produced by ionospheric/magnetos- pheric scintillations, in Effect of the Ionosphere on Space and Terrestrial Systems, J.M. Goodman (Ed.), U.S. Government Printing Office, 10. 1978. 12. W.N. Hess, The earth’s radiation belt, in Introduction to Space Sci., W.N. Hess and G.D. Mead (Eds.), Gordon and Breach, New York. pp. 179-216, 1968. 13. A.V. Gul-elmi, B.l. Klaine and A.S. Patupov, Excitation of magnetosonic waves with discrete spectrum in the equatorial vicinity of the plasmapause, Planet. Space Sci., 23(279), 1975. 14. S.A. Curtis and C.S. Wu, Gyroharmonic emissions induced by energetic ions in the equatorial plasmasphere, J. Geophys. Res. 84(2597), 1979. 15. D.A. Gurnett, Plasma wave interactions with energetic ions near the magnetic equator, J. Geophys. Res.. 81(2765), 1976. 16. E.G. Stassinopoulos, World Maps of Constant B. L, and Flux Contours, NASA SP-3054, 1970. 17. Anon, The Earth’s Trapped Radiation Belts, NASA SP-81I6, 1975. 18. K. Maeda and S.F. Singer, Energy dissipation of spiraling particles in the polar atmosphere, Arkiv for Geofysik, Band 3 nr 21, 1961. 19. P.J. Palmadesso, T.P. Coffey, S.L. Ossakow and K. Papadopoulos, Topside ionosphere heating due to electrostatic ion cyclotron turbulence, Geophys. Res. Lett., 1(105), (1974). 20. R.F. Benson and W. Calvert, ISIS 1 observations at the source of auroral kilometric radiation. Geophys. Res. Lett., 6(479), 1979. 21. Y.T. Chiu, J.G. Luhmann, B.K. Ching, M. Schulz and D.J. Boucher, Jr., Magnetospheric and Ionospheric Impact of Large Scale Space Transportation with Ion Engines, Aeronautics and Astronautics, in press, 1980. 22. J. A. Fedder, Effects of anomalous resistivity on auroral Birkeland current systems, Amn. Geophys., 32(175), (1976). 23. K. Papadopoulos, A review of anomalous resistivity for the ionosphere, Rev. Geophys. Space Phys., 15(113), 1977. 24. J.M. Kindel and C.F. Kennel. Topside current instabilities, J. Geophys. Res.. 76(3055), 1971. 25. B. Hultquist, Auroras and Polar Substorms: Observations and Theory, Rev. Geophys., 7(129), 1969. 26. B. O’Leary, Mining the moon and asteroids and living in space, Astronautics and Aeronautics, 16(20), 1978.
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0191-9067/8(V040281-07$02.00/0 Copyright c 1980 SUNS AT Energy Council EXTRACTION OF OXYGEN AND METALS FROM LUNAR ORES N. JARRETT, S. K. DAS and W. E. HAUPIN Alcoa Technical Center Alcoa Center, PA 15069 Abstract — Consideration of the lunar environment suggests modifications of the Bayer- Hall approach leading to a conceptual process for extracting aluminum and oxygen from lunar soil. The process consists of electrowinning aluminum-silicon-iron-titanium alloy and oxygen from unrefined soil in a bipolar fluoride type cell with inert electrodes. Aluminum and other elements would be recovered from the alloy by vacuum fractional distillation. The silicon produced would be used to produce solar cells for additional electrical power. 1. INTRODUCTION Energy is the major factor that encourages us to consider space industrialization. Terrestrial energy needs have increased to such huge levels that serious consideration is being given to constructing large solar power stations (SPS) in space to convert solar energy into microwave power and then beam microwaves to the earth for reconversion to terrestrial electricity. Solar energy is clearly available continuously to do work in space and space industrialization is technically feasible. However, the development of a space materials economy or space industrialization is strongly inhibited by the extremely high cost of transporting matter from earth with which to work in space. The moon is a primary source of raw material for large scale use in space. The motivations for use of lunar materials are: 1. The moon is the largest source of matter near the earth. We possess considerable general knowledge of the entire moon and extremely precise knowledge of the specific areas of the moon. 2. Terrestrial technology can be transferred to the gathering of lunar materials and the processing of raw lunar materials into industrial feedstock. Devices and tools have been identified that can allow us to obtain materials from the moon for large scale use in space at considerably lower cost than will ever be possible by transporting materials into space from the earth. Because the lunar escape energy is five percent of that of the earth, the cost of lunar ejections (by means of electromagnetic launchers) could be in the order of a few cents per kilogram. In addition, the moon has no atmosphere to cause drag and frictional heating. 3. The moon offers a large supply of the elements with which industry has experience in working and producing the broad range of goods that sustain our present style of life. About 92% of chemical elements used on the earth, exclusive of fossil fuels, can be obtained from lunar soil. The economically significant elements, like
oxygen, silicon, calcium, iron, aluminum, magnesium and titanium, can be extracted from the lunar soil. Space power stations could be constructed of approximately 90% lunar derived material. 2. LUNAR ENVIRONMENT The principal distinguishing requirement for a successful lunar operation is that all materials unavailable from lunar sources must be shipped from earth and recycled with minimal loss. The following constraints apply to processing lunar ore: 1. Lack of virtually inexhaustible supplies of air and water. 2. Lack of fossil fuels. 3. Lack of inexhaustible oxidizing and reducing agents. Carbon is very scarce on the lunar surface. 4. Lack of expendable halogens, acids and bases. 5. Lack of air and water makes the management of process waste heat especially important. Rejected heat will ultimately have to be transferred to space through radiation. 6. Processing conditions must be adjusted for the lower lunar gravity. 3. LUNAR ORE The major lunar raw materials are ilmenite, plagioclase and anorthite. Anorthite (CaALSi2On) contains 19.4% aluminum, 20.2% silicon, 14.4% calcium, and 46% oxygen. A typical composition of lunar rock from Maria section would be silica 42%, titanium dioxide (TiO2) 7.5%, alumina 13.9%, iron oxide (FeO) 15.7%, magnesium oxide (MgO) 7.9%, calcium oxide (CaO) 12.1%. The composition of lunar rock from the highland area would be silica 45.4%, TiO2 0.5%, alumina 23.4%, FeO 7.4%, MgO 9.2%, CaO 13.4%, and traces of potassium oxide, sodium oxide, manganese oxide, phosphorus oxide, and chromium oxide (1). The majority of lunar soil is completely anhydrous and has an average grain size of 30-70 microns. Eighty-five percent to 95 wt.% of the lunar powder is less than 1 mm in diameter. 4. REVIEW OF LUNAR EXTRACTION PROCESSES Since carbon is very scarce on lunar surface, Rao and co-workers (2) decided quite early that carbothermic reduction of lunar soil would probably be impractical for space processing. They chose carbo-chlorination of lunar anorthite (CaAl2Si2OK) and lunar ilmenite (FeTiO:i). A major advantage of carbo-chlorination is that it would require little water. However, the recycling of chlorine and carbon would require facilities much larger than the basic processing plant. Of the nonelectrolytic processes studied to date, the hydrofluoric acid leach method appears to require the minimum operating mass to be transported to the moon. Waldron et al. (1) have described a low temperature hydrometallurgical step to remove the silicon from the other metallic oxides by conversion to fluorides and fluosilicates. This is followed by vaporization of the silica as SiF,, and separation of
Fig. 1. Proposed system for lunar extraction of oxygen and metals. the calcium and the structural metals (aluminum, iron, magnesium, titanium) by a variety of solution, precipitation, ion exchange or electrolyte steps. However, this process requires water or at least hydrogen to make water. This must be transported from earth, but it is recyclable. Electrolytic systems to process lunar materials have a strong appeal because of their potential simplicity and low use of water and other reagents. Limited investigation of direct electrolysis of molten silicates of compositions similar to lunar soils have been performed (3,4). The high melting point and the TABLE 1
Fig. 2. Bipolar electrolytic cell. viscosity of molten silicates have created problems and prompted studies of various fluxing additions to the melt. This modification, of course, negates the reagentless advantage of the direct electrolysis route and requires consideration of extraction and recycling of fluxing reagents. The chief objections are corrosion or durability of anodes used for oxygen recovery and purification and separation of cathodic reduction products which are likely to consist of iron, iron-silicon-aluminum alloy with minor amounts of additional impurities. 5. PROPOSED PROCESS This paper describes a conceptual process scheme for obtaining oxygen, aluminum, silicon, iron, and titanium from anorthite ore. The lunar environment offers the following opportunities: 1. The abundant solar energy can be converted to electricity to operate electrolytic cells for producing an aluminum alloy and pure oxygen from lunar ores. 2. The complete vacuum (10 14 Torr) offers a chance to vacuum purify and separate aluminum, iron, silicon, and titanium metals from aluminum-silicon-iron-titanium alloys produced in the electrolytic cell. 3. By using suitable optics, solar energy can generate the high temperatures needed for vacuum fractional distillation.
Fig. 3. Free energy of formation of selected fluorides as a function of temperature. Figure 1 shows a schematic flow diagram of the proposed process for extracting desirable metals from lunar ores; it also produces oxygen for life support and for use as propellants. 6. BIPOLAR ELECTROLYTIC CELLS In the proposed system, either unbeneficiated or mechanically beneficiated lunar dust would be used as ore. The fine particle size of the dust makes magnetic and electrostatic separation attractive. No grinding is necessary. All use of water would be avoided. The ore would be fed into a bipolar cell having a cryolite (Na3AlF(i) base electrolyte. Lunar ore should dissolve easily in molten cryolite. The solubility in cryolite and the decomposition potentials of the various oxides in lunar ores are shown in Table 1. The proposed biopolar cell would be similar to that used in the Alcoa Smelting Process for electrolysis of aluminum from-aluminum chloride in molten chloroaluminate melts (Figure 2). Electric current would enter the cell through a terminal anode, flow through numerous bipolar plates between the terminal electrodes and exit through a terminal cathode. The top surface of each bipolar plate would act as a
Fig. 4. Vapor pressure of selected elements as a function of temperature. trolyzed, forming oxygen at each anode and an aluminum, silicon, iron and titanium alloy at each cathode. Oxygen gas would rise from each anode through the electrolyte providing circulation of the electrolyte and leave the cell at the top while the metal alloy would settle to the bottom and be tapped periodically. Calcium and magnesium compounds from the ore would accumulate in the electrolyte and have to be removed. A technique to accomplish this will be discussed in the next section. Search for an inert anode material is being pursued actively by various aluminum companies. Not only would inert anodes alleviate the need for frequent replacement of consumable anodes but would also permit collection of essentially pure oxygen. Tin oxide (SnO2) mixed with various other oxides such as ferric oxide (Fe2O3) and nickel oxide (NiO) have been suggested for inert anodes (5). Refractory hard metals, titanium diboride (TiB2) in particular, presumably will make suitable inert cathodes (6). 7. ELECTROLYTE PURIFICATION AND RECYCLING SYSTEM Since calcium fluoride and magnesium fluoride are thermodynamically more
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