SPACE POWER An International Journal on Systems, Technology, Economics, Environment and Policy Formerly Space Solar Power Review Volume 6, Number 2, 1986 Papers Presented at the International Symposium of the IEEE Antenna and Propagation Society PERGAMON PRESS New York Oxford Beijing Frankfurt Sao Paulo Sydney Tokyo Toronto
SPACE POWER An International Journal on Systems, Technology, Economics, Environment and Policy 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: Diana White Editorial Office: John W. Freeman, Editor-in-Chief, Space Solar Power Research Program, Rice University, P.O. Box 1892, Houston, TX 77251, USA.
0883-6272/86 + .00 Copyright ® 1986 SUNSAT Energy Council EFFECTS OF CHRONIC CONTINUOUS WAVE MICROWAVE RADIATION (2.45 GHz) ON THE FORAGING BEHAVIOR OF THE WHITE-THROATED SPARROW FRED E. WASSERMAN, DEBORAH A. PATTERSON AND THOMAS H. KUNZ Department of Biology Boston University Boston, Massachusetts 02215 SAM P. BATTISTA Arthur D. Little. Inc. 30 Memorial Drive Cambridge, Massachusetts 02142 DAVID BYMAN Penn State University Worthington-Scranton Campus 120 Ridge view Drive Dunmore, Pennsylvania 18512 Abstract — The effect of chronic continuous wave microwave radiation on the foraging behavior of the White-throated Sparrow was examined using an optimal foraging laboratory technique. Birds were exposed to microwaves for seven days at a frequency of 2.45 GHz and power densities of 0.0. 0.1, 1 0, 10.0, and 25.0 mW/cm2. Even though there were differences in foraging behaviors among power densities no trend was found for a dose response effect. Birds showed no significant differences in foraging behaviors among pre-exposure, exposure, and post-exposure periods. INTRODUCTION In an effort to determine possible environmental effects of the Satellite Power System (SPS) (1) we measured the effect of microwave exposure on foraging behavior in the White-throated Sparrow, Zonotrichia albicollis. The efficiency with which a species can forage should be important in determining its ability to survive and reproduce in a particular habitat (2, 3). The average body size of many common avian species (5 cm in length) suggests that these animals would have a maximum microwave absorption efficiency of 2.45 GHz (the frequency proposed for use in the SPS) and the rate of energy absorption could double or triple due to resonance (4). METHODS Exposure Facilities and Microwave Generating Equipment The microwave irradiation facilities were designed to provide planewave illumi-
nation with a power density variation of ± 0.5 dB maximum in the space occupied by the cages (Fig. 1). A platform covered with anechoic material was used for the support of the cages that housed the birds and the plywood walls of the irradiation chambers were lined with anechoic material. The radiating source was a Narda #645 standard-gain horn which provided linearly polarized radiation. Horns were positioned for overhead illumination. Seven replicates of the irradiation chamber were built. Three irradiation chambers were operated at 0.1, 1.0 and 10.0 mW/cm2, respectively, from one Cober S6F generator, using topwall couplers of 20 dB and 10 dB for the horn feeds to the first two chambers and a direct waveguide feed to the horn in the third chamber. Two irradiation chambers were energized by a dedicated Cober S6F generator and were used for the 25 mW/cm2 experiments. The remaining two chambers were control chambers. Control and irradiation chambers were identical with the exception of the presence of the micro wave radiating horn in the irradiation chambers.
Foraging Behavior Experiments (May 1980-May 1981) White-throated Sparrows are common birds of North America and tend to build their nests on the ground in lightly forested areas between clumps of vegetation (5). These birds are primarily ground feeders; they depend largely on uncovering food by scratching on the ground, an activity that they engage in for prolonged periods of time (5, 6). Birds were exposed to microwaves and measurements were made on various parameters of their foraging behavior. White-throated Sparrows were collected in May and October, 1980 at Manomet Bird Observatory. They were housed for at least three weeks prior to the initiation of training and between treatments in cages (43 x 33 x 59 cm) framed of metal or wood, and enclosed with plastic screen (mesh 12.7 x 12.7 mm). They were fed a diet consisting of wild bird seed, alfalfa sprouts, broccoli, cabbage, hard-boiled eggs, egg shells, and mealworm larvae. A vitamin supplement was administered either in water or as a dry powder added to their food. Food was provided ad libitum except during the foraging experimental regimen. During August to December the birds were maintained on a natural light cycle. The light cycle from January to March was increased weekly by 15 minutes until a 12:12 light/dark cycle was achieved. This 12:12 schedule continued unchanged through the completion of the experiments in May 1981. The 12:12 schedule was required to accommodate other experiments conducted in the same facility. Birds were trained to forage for mealworm larvae (Tenebrio spp.) from a specially designed foraging tray (36 x 61 cm). Trays were constructed of Ensolite® boards with 50 cylindrical cavities, each 8 mm in diameter and 13 mm deep. The cavities were arranged in a uniform grid formation with distance between the centers of the cavities 7.5 and 5.5 cm for horizontal and vertical rows respectively. A foraging tray was prepared for a training session by initially filling each cavity with a single mealworm. Through progressive trials the wells were first partially then completely covered by an adhesive label (19 x 12.5 cm).
Measurements of foraging behavior were made as follows. Each bird was released into a specially designed microwave transparent cage (0.9 x 0.9 x 0.44 m) constructed of nylon netting and plexiglas® (Fig. 2). Cages were divided in half by a visually opaque wall. One half was a waiting arena. The other half served as a foraging arena. Access from the waiting arena to the foraging arena was through a manually-operated door. Each half cage allowed independent placement and removal of foraging trays. For each experiment a foraging tray was prepared by randomly placing one mealworm, treated previously with hot water to immobilize them, in 25 of the 50 available cavities, respectively. An opaque adhesive label was placed over each of the 50 cavities to conceal the wall. The tray was placed into the foraging arena 15 minutes after the bird entered the waiting arena space. The door in the opaque divider was opened manually permitting the bird to enter the foraging arena. Search time, handling time, and nonforaging time were recorded to two-second intervals for 15 minutes using a Rustrak event recorder. Profitability, defined as
number of prey caught per second of foraging (searching + handling time), and search efficiency, defined as number of prey captured per second of search time, were calculated. White-throated Sparrows were exposed for seven days at one of four power densities (0.1, 1.0, 10.0, and 25.0 mW/cm2). One bird was exposed at each microwave power density and two additional birds served as parallel sham controls (0.0 mW/cm2). Microwave-treated birds were irradiated 24 hrs per day except for brief periods during each day when maintenance activities were performed or when being prepared for observations of foraging behavior. The duration of each experiment was three weeks; e.g., seven days pre-exposure, seven days exposure, and seven days post-exposure. Foraging behaviors were observed three times per week while the birds were being irradiated. Each bird was housed in a replicate of the observation cage (Fig. 2). and tested in the same cage and chamber in which it was housed. Seed dispensers, water tubes, and vegetable cups were provided except during testing and for 2 hrs before. Experimental and sham control birds were selected randomly, weighed, returned to their cages, and tested. Once all birds were tested the random selection process began again. The cages were placed in control chambers during the pre-exposure weeks, in irradiation chambers during exposure weeks and in control chambers during post-exposure weeks. Parallel control sham birds (0.0 mW/cm2) were housed in control chambers during all three periods. Ambient temperature measurements were taken both inside and outside of the exposure and control chambers. This experiment was replicated once (accounting for the 6 trials per exposure period reported for microwave exposed birds in Table 1).
RESULTS For each power density and behavioral variable an analysis of variance (ANOVA) was computed to determine if there were any significant differences in foraging behavior among pre-exposure, exposure and post-exposure periods. The only significant difference found (ANOVA; p < 0.05) was in profitability for parallel sham control (0.0 mW/cm2; Table 1; p < 0.01). Mean profitability was significantly lower during the pre-exposure period (Duncan’s Multiple Range Test; p < 0.05). For each exposure period and foraging behavior variable ANOVAs were computed to determine if there were any significant differences among power densities within treatment periods. The only significant differences (ANOVAs p < 0.05) were (1) during the exposure period birds that were exposed to power densities of 0.1 and 1.0 mW/cm2 ate a significantly higher number of prey than those birds exposed to a power density of 10 mW/cm2 (Duncan's Multiple Range Test; p < 0.05; Table 1; 8.2 versus 3.8 prey eaten); and (2) birds which had been exposed to a power density of 10 mW/cm2 had significantly (p < 0.05) less ‘search time’ than birds which had been exposed to power densities of 0.1 mW/cm2 (Duncan’s Multiple Range Test; p < 0.05; Table 1; 67 versus 141 sec). No other significant differences in behavior were found. ANOVAs on environmental variables (Table 2) yielded only one significant value. Chamber temperatures varied significantly among periods for birds exposed to power densities of 25.0 mW/cm2 (p < 0.05). Chamber temperatures were significantly higher during the exposure period than during the pre-exposure or postexposure periods (Duncan’s Multiple Range Test; p < 0.05). No other significant differences in temperature or humidity were found. DISCUSSION A number of studies have demonstrated the effect of environmental variables on avian daily and seasonal foraging habits. For instance, ambient humidity greatly affects the thermoregulatory performance of small birds exposed to heat stress, and high humidities can be lethal at temperatures that species could tolerate under more moderate humidity conditions (7). Birds confined where humidity was high (35-40%) could not tolerate temperatures above 42°C, but birds kept at a relative humidity of 20% tolerated higher ambient temperatures (8). Many avian species at photoperiods of 10-12 hr feed most actively during the morning, slightly reduced rates during mid-day and declining rates in late afternoon. These feeding rates correlate with increasing temperatures. Feeding sessions occur during the evening when the temperature is lower (9). In addition, most birds exposed to heat stress become hyperthermic and may minimize metabolic heat production by reduced activity (7). Personal observations during these experiments at power densities of 0.1 mW/cm2 and above during August confirmed that at high temperatures and humidity the birds had reduced activity levels. Exposure to low-level microwave radiation has been shown to affect behavior in some animals (e.g., 10, 11, 12, 13, 14. 15, 16, 17). Foraging behavior of White- throated Sparrows, however, was not affected by seven days of exposure to microwaves at power densities of 0.1, 1.0, 10, or 25 mW/cm2 at the reported temperatures and humidities. The significant differences in foraging behaviors among power densities were probably caused by individual variation among birds. No dose response
effect was found in these results. Adverse affects seen in other studies (10, 13, 14, 16, 17) at similar power densities were not found in this study. In conclusion, it appears that the effects of microwave exposure dosages used in this study on the foraging behavior of a small avian species are minimal. Under more severe temperature and humidity conditions than those encountered in these experiments the effects of microwaves could be more significant. Acknowledgments — This research was supported by a contract from the U.S. Environmental Protection Agency (No. 68-02-3278) to Arthur D. Little. Inc., and subcontracts to Boston University (No. A-l 1038) and Manomet Bird Observatory (No. A-l 1040). For help of various kinds we thank Edward Cook, Russ Smallman, and Barney Schlinger. Although the research described in this article has been funded wholly by the U.S. Department of Energy via the U.S. Environmental Protection Agency, the article does not necessarily reflect the views of either agency and their official endosements should not be inferred. REFERENCES 1. P.E. Glaser, Power from the Sun: Its Future. Science 162, 857-886. 1968. 2. F.R. Hainsworth. Food Quality and Foraging Efficiency — The Efficiency of Sugar Assimilation by Hummingbirds,./. Comp. Physiol. 88,425-431, 1974. 3. R. Sibly and D. McFarland, On the Fitness of Behavior Sequences, Amer. Natur 110, 601-617, 1976. 4. C.H. Durney. C.C. Johnson. P.W. Barber. M.F. Iskander, J.L. Lords, D.K. Ryser, S.J. Allen, and J.C. Mitchell. Radiofrequency Radiation Dosimetry Handbook. Ed. 2. Report SAM-TR-78-22. Brooks Air Force Base, Texas: USAF School of Aerospace Medicine Aerospace Medical Division (AFSC), 1978. 5. F.E. Wasserman. Territorial Behavior in a Pair of White-throated Sparrows, Wilson Ball 92, 74-87, 1980. 6. J.K. Lowther and J.B. Falls, Zonotrichia albicollis (Gremlin) White-throated Sparrow, pp. 1364— 1392, in Bent, U.S. Natl. Mus. Bull. 237, 1968. 7. R.C. Lasiewski and R.S. Seymour, Thermoregulatory Response to Heat Stress in Four Species of Birds Weighing Approximately 40 Grams. Physiological Zool. 45, 106-118. 1972. 8. J.W. Hudson and S.L. Kimzey, Temperature Regulation and Metabolic Rhythms in Populations of the House Sparrow, Passer domesticuls, Comp. Biochem. Physiol. 17, 203-217, 1966. 9. S.C. Kendeigh, J.E. Kontogiannis. A. Mazac. and R.R. Roth, Environmental Regulation of Food Intake by Birds. Comp. Biochem. Physiol. 31, 941-95, 1969. 10. S. Baranski and P. Czerski, Biological Effects of Microwaves. Dowden. Hutchinson and Ron Inc., Stroudsburg. 1976. 11. J. Gillard, B. Servantie, G. Bertharion, A.M. Servantie, J. Obrenovitch. and J.C. Perrin, Study of the Microwave-induced Perturbations of the Behavior by the Open-field Test into the White Rat. In: Johnson and Shore (Editors), Biological Effects of Electromagnetic Wr/w. US DHEW Pub. No. 77-8010. pp. 175-186, 1976. 12. A.H. Frey. Behavioral Effects of Electromagnetic Energy. In: D.G. Hazzard (Editor), Biological Effects and Measurements of Radio Frequencv/Microwaves. Rockville, MD: HEW Pub. (FDA) 77-8026, pp. 11-22, 1977. 13. D.R. Justesen, Behavioral and Psychological Effects of Microwave Radiation, Bull. N. Y. Acad. Med 55, 1058-1078, 1979. 14. S.M. Michaelson, Microwave Biological Effects: An Overview, Proceedings of IEEE 68, 40-49, 1980. 15. F.E. Wasserman, C. Dowd, B.A. Schlinger, D. Byman, S.P. Battista, and T.H. Kunz, The Effects of Microwave Radiation on Avian Dominance Behavior. Bioelectromagnetics 5, 331-339, 1984. 16. F.E. Wasserman, C. Dowd, D. Byman, B.A. Schlinger, S.P. Battista, and T.H. Kunz, Thermoregulatory Behavior of Birds in Response to Continuous Wave 2.45 GHz Microwave Radiation, Physiological Zoot. 58, 80-90, 1985. 17. F.E. Wasserman, T. Lloyd-Evans, S.P. Battista, D. Byman, and T.H. Kunz, The Effect of Microwave Radiation (2.4 GHz CW) on the Molt of House Finches (Carpodacus mexicanus), Space Solar Power Review. in press.
digitized by the Space Studies Institute ssi.org
0883-6272/86 + .00 Copyright ® 1986 SUNSAT Energy Council GEOSTAR: A MULTI-PURPOSE SATELLITE SYSTEM TO SERVE CIVIL AVIATION NEEDS* GERARD K. O’NEILL President and C.E.O. Geostar Corporation 101 Carnegie Center Princeton. New Jersey 08540 INTRODUCTION The Geostar System is a proposed space/ground or air concept that would link mobile terminals through satellites to a computer on the ground. It is designed to provide many services: navigational positioning, radiolocation (return of position information to a central site), emergency location, terrain warning to pilots, warnings of potential collisions between Geostar-equipped aircraft, approach guidance, two- way digital message service and interconnection to ground data bases. Where other systems are already in place to satisfy one or more of these needs, the Geostar System can operate in a supplemental or advisory mode. The Geostar System combines the existing technologies of orbital satellites, computers and integrated circuits. It consists of three parts: a ground station with a computer, two or more satellites at fixed locations in Earth orbit, and the terminals (transceivers) carried by aircraft, surface vehicles or even individual people. The ground station sends digital messages to the transceivers and receives replys from them through the satellite relays. In an airborne application, the times of reply are measured at the ground station and are combined with transmitted digital information on altitude for calculation of aircraft position. That information is sent to the aircraft and to central dispatch locations. The transceivers are designed to be simple and low in cost. All use the same wideband radio channel for transmit and another for receive. The single channel can accommodate a large number of users for three reasons: • Each transceiver is silent most of the time, transmitting only in short, occasional bursts. • Transceivers use “spread-spectrum” transmissions which permit many messages to occupy the same channel simultaneously without interference. • The satellites have spot beams for different geographical areas. A minimal Geostar System consists of one ground station, one satellite able to relay outbound messages from the ground station to the users and to relay inbound *This paper originally appeared in the ICAO bulletin.
messages back to the ground station, and another satellite capable of relaying inbound messages from the users to the ground station. Depending on the spot beams, a minimal system can serve a small geographical area, or can serve nearly one-fifth of the globe. Six satellites with wide-area coverage, and three ground stations, are sufficient to provide all services world-wide, excluding only the extreme polar latitudes (Fig. 1). That number provides instantaneous recovery against the failure of the transmit capability of any single satellite. It might be noted also that several Geostar-like systems could coexist using the same frequency bands. FREQUENCY CHANGES PROPOSED In September of 1984, the U.S. Federal Communications Commission (FCC) issued a Notice of Proposed Rulemaking proposing the allocation of frequency bands in the microwave region in the United States for a new service, to be called the Radio Determination Satellite Service (RDSS). Because the Notice was the FCC’s reply to the application of a single company, the Geostar Corporation, the term “Geostar System” will be used hereafter. The Commission proposed in the Notice that the technical specifications submitted by our firm become the standards for the RDSS. The Commission also submitted to the International Telecommunication Union an Advanced Notification of the RDSS orbital locations and satellite characteristics for the United States, and these were published by the International Frequency Registration Board on 9 October 1984 under the names “USRDSS East, Central and West.”
The FCC’s final action on the RDSS, determining the technical standards for the system, were taken in April 1986. Geostar Corporation is scheduled to begin service to the contiguous United States in 1988. The Geostar System is multimodal; it can service and connect all transportation modes (aircraft, surface vehicles, boats, pedestrians, fleet dispatch headquarters and rescue services). Transceiver prices and user charges can be low because all services are provided by a single large computer installation, taking advantage of economies of scale in computing speed and memory capacity. That computer can also associate each service transaction with a charge added to the account of an individual user. Aircraft transceivers are mounted like other avionic equipment, either in the instrument panel or in an avionics bay. The lightest transceivers, for personal use,
are hand-held and are equipped with calculator-like keyboards and liquid-crystal readouts. Power for such transceivers is from penlight batteries. SYSTEM ARCHITECTURE ESTABLISHED Each transceiver has a unique digital identification code which is built in at the factory, and is included in all of its transmissions. The identifier is similar to that used in the ICAO world-wide Selective Calling (SELCAL) system. By selecting the digital address which heads each outbound message, the ground station can send a message to all transceivers, or to a group, or to a single transceiver. The satellite relays are similar to conventional communications satellites in that they have no intelligence. They simply pass the ground station's transmissions to the user transceivers, and return the replies to the ground station. The Geostar process commences with an interrogation signal (Fig. 2), sent out many times per second from the ground station and relayed through a satellite to all transceivers. The normal state of the transceivers is quiet listening with no transmission. A transceiver can be changed to an active state by any of three events: the expiration of a preset time delay, or the user's command, or the ground station sending a “wake-up” message addressed with the transceiver’s identifier. When any of those three events has brought the transceiver to the active state, it responds to the next interrogation with a short burst reply. The reply contains the unique transceiver identification code, any message which the user wishes to transmit, and also error detection codes and an error correcting code. After that reply, the transceiver turns itself off. The transceiver signal, emitted from a nondirectional antenna, is relayed by at least two Geostar satellites to the ground station. There, the times of arrival are combined with terrain height information, stored in the ground computers, to yield a three-dimensional position for vehicles, boats and hand-held transceivers. In the case of aircraft with minimal equipment, height is obtained by the pilot's entering his altitude as a message while cruising. In aircraft equipped with ICAO standard encoding altimeters or with precision encoding altimeters, barometric altitude is included in the transceiver reply, and is combined at the ground station with current data on local barometer settings for the calculation of a three-dimensional position. When replies through three satellites are available, a low precision calculation of position independent of altimetry is made, as a back-up. Position computed at the ground station is sent to the user as a message through one of the satellite relays, addressed with the identifier code of the transceiver. All messages are completed by the transmission of a positive reply, signifying that the message has been received correctly, satisfying the embedded error code. If that acknowledgement is not received, there is an automatic retry. The Geostar process takes 0.6 sec, and a further 0.7 sec if a retry is required. Since Geostar is primarily intended as a civil system, its data protocols will be published. However, the privacy of messages unrelated to air traffic safety can be assured by government-approved encryption, as is customary in civil telecommunications.
POSITIONING ACCURACY ESTIMATED In the Geostar System, the errors in height are those of the on-board altimeter or, in the case of surface users, those of the digital terrain map stored at the ground station. Latitude and longitude errors depend on the errors in the timing of the transceiver reply and of its arrival at the ground station. Each of these is typically about 5 nsec, leading to a combined round-trip jitter of about 7 nsec, and therefore to an error of roughly 1 m in the distance from a satellite to the transceiver. With satellites separated by at least 30° in longitude, triangulation for longitude is good. In typical conditions, longitude should be determined to a few meters by the Geostar System. For latitude, triangulation is good everywhere except close to the Equator. In midlatitudes, typical errors in latitude are calculated to be a few meters plus approximately twice the altimeter error. Despite the poorer triangulation for latitudes close to the Equator, the latitude determination is usable fairly close to that region. For total timing and altitude errors of 3 m, the latitude determination becomes useless only within about 4 km of the Equator. At 8 km from the Equator, the latitude errors are about 2 km, comparable to those of VLF/Omega, and they are below 100 m,* beyond about 160 km from the Equator. The reduction of latitude precision for aircraft close to the Equator can be overcome inexpensively, where necessary, by emplacing a relay for transceiver replies 50-150 km from the Equator to send the signals to the satellites. That restores good triangulation. Fortunately, the major populated areas which are close to the Equator (Singapore, Kuala Lumpur, Quito, and Nairobi, for example) all have high volcanic mountain peaks conveniently located for such relays. Geostar can provide high accuracy with inexpensive equipment because it is a two-way, interactive system. Most of the errors in other satellite location systems (ionospheric delay variations, imprecise knowledge of the geoid, errors in satellite position, etc.) cancel out in Geostar, because positions are measured relative to fixed-site “benchmark” transceivers. Geostar is an all-differential, closed-loop system rather than an open-loop system. The combination of high precision, low cost, low power drain and nondirectional antennas that is realized in the Geostar RDSS would not be possible if Geostar were to attempt to provide channelized voice communications. A voice channel 5-kHz wide gives a ranging precision about 3,000 times worse than that of Geostar’s single digital channel, which is 16.5-MHz wide. And, the average power required to transmit voice is several hundred times more than for equivalent information transmitted digitally. EXPERIMENTAL TESTS PERFORMED In 1983, a test for the Geostar System was put in place, consisting of a ground station, user transceivers, and satellite emulators located on mountain peaks in the Sierra [Nevada] Mountains. The conditions emulated operation in extreme Northern latitudes near the limits of satellite coverage. The system demonstrations included guiding a pedestrian to a hidden marker in a *Typical estimated errors of the U.S. proposed Global Positioning System (GPS) civil-access accuracy.
field, guiding a vehicle to a precise street address, and guiding an aircraft to a precision instrument landing. In good conditions, positions were repeatable to approximately one metre. A videotape of the Sierra Test System providing a precision instrument approach has been shown at a number of navigation conferences. To test the transmissions at elevation angles similar to those of a real satellite system, the Sierra System was converted in 1984 to become the Airborne Test System. With that version, two light aircraft carried satellite emulators to altitudes of about 3,000 m. A ground station with augmented computing power calculates the changing positions of the emulators by measuring the replies from benchmark transceivers. The new system allowed more realistic testing, although with precision degraded from that of the satellite system by the motion of the emulators in turbulent air (Fig. 3). The Comsat General Corporation is under contract to Geostar for satellite design specification and construction supervision. Another company, Comsat Technology Products, built the prototype U.S. ground station, and is also under contract for overall system review and the functional specification of transceivers. Studies indicate that the first RDSS market will be land transportation, especially truck fleet control. The trucking industry and agencies of the U.S. Federal Government supported Geostar in its requests to the Commission. Outdoor recreational, professional and public safety applications include the small boat industry, fishing, skiing and other sports, forestry, and radio location and two-way communications for cars, taxis, police vehicles and rescue agencies. Aircraft, on a relative basis, do not constitute a large market at this time.
For light aircraft, the Geostar Corporation plans to charge a fixed monthly fee in the US $20—$50 range, independent of use. For land transportation, fees will be based in part on transactions. Because the total installed cost of the Geostar space and ground segments is relatively low, these low user fees will provide a comfortable margin of profitability. The Company’s policy is to form contractual arrangements with established service providers. It recognizes that in many areas outside the U.S., access to an RDSS may be subject to national or international arrangements. GLOBAL EXTENSION NEEDED I believe it is urgent to establish, on a world-wide basis, allocations for the frequency bands necessary for radio determination satellite services. It is not necessary to accept a particular system concept, nor the services of a particular company such as the Geostar Corporation. The requirements are few but specific: the 1618- and 2492-MHz bands needed, which were chosen because they are virtually unused, should be made available as single bands, for spread-spectrum use, and not channelized into a multiplicity of narrow bandwidth voice channels as in most of the spectrum. Only with single wide bands, both for the uplink and the downlink to the user transceivers, can a radio determination system — whatever its detailed architecture — achieve high positioning accuracy. In any geographical area where those bands are established, nations can then have, through the Geostar concept or something competitive to it, the services needed. These include the following:
Very high positioning accuracy, of the order of a few metres, and accompany it with two-way messaging, fleet dispatch information and emergency location; neither connection to nor dependence on any military system; no threat to national security, because the ground station which carries out the computations can be programmed to cut off service instantly to any transceiver that approaches a military reservation or travels at missile speed; no threat to national sovereignty because national borders will be precisely defined in ground station computers—this permits each country to control the level of service to be allowed within its territory; a system that can be established by one nation, or by a contiguous group of nations, at low cost; the linking of all modes of transportation, emergency services and fixed sites with a single system using low-cost transceivers; the ability to tie all elements together to form area-wide or even global systems, with as few as six satellites for world-wide coverage; the inclusion of polar coverage with a small number of additional satellites; operation with up to 12 different, competing RDSS systems providing service simultaneously to the same geographical area. SPREAD-SPECTRUM TECHNIQUES USED The outbound Geostar microwave transmission from the ground station comes to the users as a continuous "spread-spectrum” data stream, in the S-band at 2492
MHz, with a bandwidth of 16.5 MHz. Both interrogations and addressed messages are contained in that data stream. Spread-spectrum transmission originally was developed for jam-resistant military systems, such as the U.S. Global Positioning System (GPS). In such transmission, the information is superposed on a carrier which alternates phase in a predetermined pattern at a high rate, producing a wide bandwidth signal (Fig. 4). In Geostar, as in GPS, that rate is about half the bandwidth. The replies from transceivers are also spread-spectrum, with the same alternation rate and bandwidth. Their carrier frequency is 1618 MHz, in the L-band. While both Geostar and GPS use spread-spectrum techniques, their system architectures are completely different. GPS is a one-way, open-loop system providing a single function: user position fixing. Geostar is a two-way, closed-loop system providing many functions, of which user position fixing is only one. But the antennas for Geostar are similar to those of GPS. They are printed circuits on the aeroplane surface, with no projection into the slipstream. Therefore, they do not impose any technical, operational or economic penalties of drag or weight. Table 1 gives the main Geostar System parameters relevant to communications reliability and ranging accuracy. Using spread-spectrum transmission and the Geostar System architecture, two or more RDSS systems can share the same spectrum. Two such independent systems each could provide the full functions of surveillance, navigational guidance, approach guidance, two-way messaging, terrain avoidance and emergency location. Short of that extreme in redundancy, a Geostar-type RDSS can provide a high degree of redundancy economically in each system segment. For the user segment, carrying two transceivers will provide full on-board redundancy for all Geostar Services. For the space segment, the satellite relays will be fully redundant internally, in accordance with normal practice for high reliability long-life space systems. A six- satellite global system will recover instantaneously from loss of transmit capability of any satellite. Receive capability requires very little weight on the satellite, and almost no power. Redundant receive capability can therefore be provided most economically by lightweight packages carried on ordinary communication satellites. With such provision, recovery from total loss of a satellite will also be instantaneous.
For the ground segment, stations will be located in secure sites and provided with independent emergency power. Within each computer complex, redundant systems will be provided in all components including data bases. For each ground station, a second system, fully redundant, should be built several thousand kilometers from the first. In the event of a major disaster, such as a tornado that destroys the antennas communicating with the satellite relays, the alternate site could take over the system load immediately. SYSTEM CAPACITY CONSIDERABLE The traffic capacity of Geostar-like radio determination systems can grow without limit, as long as successive generations of satellite relays are equipped with larger antennas which cover a given geographical area with larger numbers of spot beams. This can be seen most easily by considering a single spot beam covering a given geographical area. When a second generation satellite relay of twice the antenna diameter is emplaced, covering the same area with four spot beams (Fig. 5), the ground station can send the messages to a particular user through just one of the four beams, because the ground station “knows” the approximate location of the user. The ground station can therefore transmit to four users simultaneously, one in each of the four spot beams, quadrupling the outbound capacity compared to a single beam. For the inbound direction, the four spot beams allow four users to transmit data simultaneously. By the same reasoning, the total power required of the satellite does not increase as successive generations of satellites are emplaced. A certain signal strength must reach the user from a satellite to support the flow of outbound data. That signal strength is a power divided by a total geographical area. The power required for each of four beams feeding the same total geographical area is therefore just one-fourth the power required for a single beam, and the total power required of the satellite stays the same, although the total capacity has increased fourfold. In a practical system, these numbers are altered somwhat by beam overlap and by the concentration of users near cities. Bearing in mind that in the long term Geostar-like systems do not become saturated, it is useful to compare the maximum imaginable system loading from aviation with the capacity of one beam of a Geostar-type RDSS. Taking the example of the United States, there are some 2,600 airliners, 11,000 nonairline turbine aircraft, and
234,000 piston-engine aircraft registered. A total of 49.5 million hours are flown per year. At peak, there are about 12,400 aeroplanes in the air nationwide, of which 1,800 are airliners, 1,200 are nonairline turbine aircraft, and 9,400 are piston-engine powered. Data on the number of landings indicates a typical flight time of 90 minutes. With control of the Geostar update rate from the ground computer (overridden at any time if the pilot wants more information), a reasonable Geostar usage per flight is shown in Table 2. The update rate on position fixes is increased from its cruise value during climb and descent, and further increases below 600 meters altitude. Below 150 m, the fix rate increases to one fix per 0.5 sec. (That rate is considerably faster than the update rate provided by the conventional military GCA precision landing system.) Whenever the ground station detects a potential collision threat, the computer programme also automatically increases the fix rate. The computer programme at the ground station, of course, also give the pilot collision warnings. To give each pilot a situation display, the Geostar transceiver in the cockpit can read the downlink data channel and so display to the pilot, if the aeroplane is equipped with an appropriate display unit, the positions and velocities of all Geostar-equipped aircraft in his vicinity. An upper limit of system load is taken by the extreme assumption that every aircraft is Geostar equipped, and that every flight ends with a Geostar instrument approach and landing. (We have not proposed that the system be mandatory.) From Table 2, for the typical flight profile, the time average per aircraft is 520 fixes/90 min, or about 1 fix every 10 sec. For all aircraft combined, the peak total is about 1,200 fixes/sec. The system could handle that number even if all the 12,400 aircraft in the air simultaneously (peak instantaneous air count) over the contiguous United States were to be in the same spot beam. Within the dimensions of the antenna of the ATS-6* satellite, launched successfully in 1974, the number of spot beams in a Geostar satellite is such that the maximum aviation demand, as estimated above, would be only a few percent of system capacity. *Applications Technology Satellite of the U.S. National Aeronautics and Space Administration.
digitized by the Space Studies Institute ssi.org
THE SOLAR POWER SATELLITE (SPS) CONCEPT REVISITED Papers Presented at the International Symposium of the IEEE Antenna and Propagation Society Boston, Massachusetts June 1984
0883-6272/86 + .00 Copyright ® 1986 SUNSAT Energy Council INTRODUCTION The Solar Power Satellite (SPS) Concept Revisited The following set of five papers were presented by Messrs. Dickinson, Glaser, Brown, Arndt, and Osepchuk at a special panel discussion session "The Solar Power Satellite (SPS) Concept Revisited” at the June 1984 International Symposium of the IEEE Antenna and Propagation Society in Boston, Massachusetts. Richard Dickinson also acted as Session Chairman. The session was organized by W. C. Brown and J. F. Lindsay, both IEEE Society representatives to the IEEE Energy Committee, in response to the recommendations in the 1980-1981 reviews of the "DOE/NASA Satellite Power System Concept Development and Evaluation Program” by the Office of Technology Assessment within Congress and the National Research Council. Both bodies recommended that the Solar Power Satellite Concept be periodically reviewed in the context of advances in generic technologies upon which the concept depends. The scope of the session included a microwave background paper by Richard Dickinson of the Jet Propulsion Laboratory, an overall assessment report on the SPS by Peter Glaser of Arthur D. Little, Inc., a paper on environmental issues by John Osepchuk of Raytheon, a microwave application paper by Dickey Arndt and E. M. Kerwin of Johnson Space Center and a report on recent advances in microwave technology by William C. Brown of Raytheon. In the five years since the conclusion of the DOE/NASA study there have been many advances in transportation, solar cell, and microwave technologies that make the SPS technically and economically more practical. At the same time, the pollution-free aspects of SPS generated electric power are making it more attractive as a future energy source. It is to be expected that there will be growing interest in additional workshop sessions devoted to the SPS.
digitized by the Space Studies Institute ssi.org
0883-6272/86 + .00 Copyright ® 1986 SUN SAT Energy Council SPS REVISITED RICHARD DICKINSON Jet Propulsion Laboratory California Institute of Technology Pasadena, California 91109, USA INTRODUCTION Twenty years ago, in 1964, Bill Brown presented some of his initial results on beamed microwave power to this same organization, the IEEE International Convention (1). Sixteen years ago Dr. Glaser published his concept (4) of the satellite power system (SPS), which embodied the concept of wireless power transmission in a scheme for importing solar power from geosynchronous orbit (GEO) to Earth. Four years ago the Department of Energy completed its evaluation of the SPS concept (5). Today we will revisit the SPS concept. SPS CONCEPT There should be no doubts that, while it is still only a concept, the SPS is technically viable. All of the critical elements have been demonstrated in laboratory or field tests, such as the 54% end-to-end, dc-to-dc transmission efficiency (3) of power from a microwave oven magnetron to a rectenna array or the transmission of 34 kW over 1.6 km at Goldstone, California, in 1975 (2). The construction and erecting of large structures in space, solar to electric power conversion in space, transmission of microwaves from space and near-routine transportation to space have all been demonstrated. Thus, the concept is technically viable, but it is not yet a commercially attractive enterprise. The economies of scale and the minimum sizes for useful amounts of power conversion are such that the SPS requires a multi-GW satellite in GEO orbit before the SPS can begin to generate a stream of revenue to pay back the investors. Only a massive government subsidy can provide the financing necessary for such a concept. A revised economic concept for attaining an SPS program is needed, since the basic technology is already available. This special session on the SPS was organized by W. C. Brown, MTT-S Representative to the IEEE Energy Committee, and J. F. Lindsay, AP-S Representative to the IEEE Energy Committee. Peter Glaser of A. D. Little, Inc. will present a reassessment of the SPS. Bill Brown of Raytheon Co. will discuss recent advances in key microwave components, Dickey Arndt of Johnson Space Center will report on applications of low-Earth-orbit power transmission, and John Osepchuk of Raytheon Co. will discuss environmental issues.
Acknowledgment — The research described in this paper was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. REFERENCES 1. W.C. Brown, Experiments in the Transportation of Energy by Microwave Beam, IEEE Int. Conv. Rec. 12(2), 8-18. 1964. 2. R. Dickinson. Evaluation of a Microwave High-Power Reception-Conversion Array for Wireless Power Transmission, Technical Memorandum 33-741, Jet Propulsion Laboratory. Pasadena. CA, I September 1975. 3. R. Dickinson and W. Brown, Radiated Microwave Power Transmission System Efficiency Measurements, Technical Memorandum 33-727, Jet Propulsion Laboratory, Pasadena, CA, 15 March 1975. 4. P. Glaser, Power from the Sun: Its Future. Science 162, 857-861. 1968. 5. U.S. Department of Energy and National Aeronautic and Space Administration. Program Assessment Report. Statement of Findings, Satellite Power Systems Concept Development and Evaluation Program. DOE/ER-0085, U.S. Department of Energy, Washington. DC, November 1980.
0883-6272/86 + .00 Copyright 4 1986 SUNSAT Energy Council UPDATE ON THE SOLAR POWER SATELLITE TRANSMITTER DESIGN WILLIAM C. BROWN Raytheon Co. Microwave and Power Tube Division Foundry Avenue, Box 33 Waltham, Massachusetts 02154, USA Abstract — A number of remaining problems in the conceptual design of the transmitting antenna for the Solar Power Satellite have been solved as a result of additional technology development. Much of the technology was derived from the conceptual design of a ground- based transmitting antenna for beaming power to a high altitude airship or airplane. INTRODUCTION It has been seven years since the inception of the DOE/NASA Satellite Power System Concept Development and Evaluation Program, and four years since its conclusion (1). At the conclusion of the study both the Office of Technology Assessment and the National Research Council made studies of the results and made recommendations. Both groups recommended that the Solar Power Satellite be periodically reassessed in terms of advances in the generic technologies upon which the concept depends. This paper relates to an updating of the design of the satellite transmitting antenna array for consideration in such a reassessment. Although much of the conceptual design of the satellite phased array transmitter based upon the use of a crossed-field device, the magnetron, had been completed, there remained some unresolved problems. In the last four years, there have been some major developments in microwave technology that seem to have resolved these problems, while at the same time suggesting basic improvements in other aspects of the transmitter design. To understand the importance of the recent new developments, they must be related to various levels of integration of the transmitting antenna array. The lowest level is the radiating module which consists of an area of slotted waveguide radiator, the microwave generators which feed it, and the control circuitry. The next level of integration is the “subarray” which consists of a large number of radiating modules. The subarrays are then integrated into the transmitting antenna array. These recent developments have led to the virtual completion of the conceptual design of the radiating module. The advances may also impact the subarray level in that there is now a straightforward way to refocus the subarray on the ground rectenna even though the subarray face may be oriented several degrees from physically facing the ground rectenna. This should allow much larger subarrays while eliminating the need of mechanical jacks to reorient the subarrays and reducing the cost of the retrodirective array pointing system.
We will start the discussion with resolving an important problem associated with the need to separate the temperature environments for the solid state and ferrite devices from that needed for the microwave power generation. RESOLUTION OF PROBLEM OF ACHIEVING AMPLITUDE AND PHASE CONTROL OF MICROWAVE OUTPUT FROM SINGLE RADIATING MODULE WHILE MAINTAINING AN ACCEPTABLE ENVIRONMENT FOR SOLID STATE AND FERRITE DEVICES This problem was recognized in the architecture of Fig. 1 where the microwave power generation devices and the microwave antenna radiating modules are separated by a blanket of thermal insulation, and all of the solid state devices are mounted on the surface of the slotted waveguide arrays which can be maintained at an acceptable temperature for these devices. The anticipated range of temperatures for the two areas is shown in Fig. 2. In this design each of the magnetron microwave generators is equipped with a pyrolytic graphite radiator which combines the properties of low density, high heat conductivity, and high emissivity, for radiating dissipated power. The total mass of this radiator has a strong influence on the sizing of the magnetron whose mass tends to optimize at three to five kilowatts microwave output. The output of two of these magnetrons is combined in a Magic T and then fed to the slotted waveguide radiator. The use of the Magic T to combine the output of two tubes was early introduced as a means of eliminating a high power ferrite circulator which would be necessary if a single magnetron were used and combined with a ferrite circulator as a directional
amplifier. However, when a Magic T combiner is used, the phase and amplitude of the output of the two magnetrons must be matched within very close limits at the point where they combine at the Magic T output, or else an amount of reflected power too large for a ferrite circulator to handle on the input side will result. Ideally, what is desired is to be able to drive the Magic T on the input side with less than five watts of microwave power and to achieve about eight kilowatts of output from the Magic T and associated magnetrons with a reflection to the input of only a few watts to prevent overheating of the ferrite circulator and the resistive load that absorbs the power. At the time of the conclusion of the study sponsored by the DOE/NASA program, we did not visualize how such high gains could be achieved nor how the phase and amplitude of the power output of the two magnetrons could be balanced at the Magic T output. The nature of the unresolved problem that created a design dilemma at the end of the study may perhaps be better understood by quoting from the final report (2). The following quote should be read with the knowledge that we had been successful in demonstrating phase and amplitude tracking simultaneously in a magnetron directional amplifier that consisted of a single magnetron and a single 3-port ferrite circulator. Such a demonstration had been one of the principle objectives of the study contract. In the interests of demonstrating the general principles of phase and amplitude tracking with the magnetron directional amplifier, the ferrite circulator was used as the passive directional device. While the use of the ferrite circulator for terrestrial use is sound, its use in space may be objectionable because currently available ferrite circulators will not operate in an environment of 300°C. Thus, an investigation needs to be made to see if new or different materials could be used to solve this problem. Because of the potential difficulty with the ferrite circulators in the SPS application, the conventional wisdom has been to use the “Magic T” or its equivalent to perform the same functions with high efficiency and with no need for temperature sensitive materials.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==