space power system development. For example, several types of advanced solar cells are being tested to obtain information on interactions with the space environment. Satellite experiments have been performed to test materials and obtain information on spacecraft charging phenomena. They demonstrated deleterious effects on solar arrays and power subsystems. As new technologies are introduced, experiments will continue to be performed on subsystems to obtain reliable data under space operating conditions. The Space Energetics and Environmental Laboratory (SEEL) (9), that is being evaluated by Japan for use in conjunction with the space station, appears to be the most comprehensive effort to develop technology relevant to the SPS concept and to assess environmental effects associated with space power. Several experiments are being planned, including a space plasma experiment to establish microwave beam and plasma interactions with the ionospheric environment, to verify the operation of electric propulsion systems, evaluate high-power beam transmission using electrons, plasma, microwave and laser beams, and to assess the operation of a solar dynamic system for a proposed 250-kW Stirling engine with a 400-m2 concentrator to demonstrate high conversion efficiencies. The power subsystems being developed for the space station will require electrical components and conductors capable of operating in a high-voltage/high-current mode to match high-capacity systems, achieve increased life at an operating voltage and minimize interactions with the space plasma environment. Power transistors, switches, diodes, capacitors and transformers that can match high-power subsystem requirements will have to be developed. For example, diodes with ratings of 1000 V and 50 A, and switching times of 200-400 nsec have been developed. Intercalated graphite-fiber conductors show promise for light-weight, high-strength transmissions lines. The experience obtained in the Space Station program will be an invaluable guide to SPS development. Important strides are being made in the development of microwave power generation, transmission and conversion. Advances are being made in the design of magnetrons, a new receiving antenna design concept has evolved and a feasibility study is being undertaken by NASA of a high-altitude platform powered by a microwave beam for instruments to indicate carbon dioxide-induced climatic changes. Consideration has also been given to powering a cargo orbital transfer vehicle with a microwave beam to convey payloads from low-Earth to higher orbits (10). The performance of argon-ion thrusters required for electrical propulsion has been demonstrated in laboratory tests. The application of automation, expert systems and tele-operators will have important influence on the capability to perform complex operations in orbit. The potential to provide a “live” presence will lessen requirements for extravehicular activity and allow remote control of functions previously requiring manned operations. The successful demonstrations and experience with “robotics” in the development of the space infrastructure will determine the role of man in LEO and GEO to perform the required construction, assembly, operations and servicing tasks. If man is required in GEO for more than sortie missions, shielding will be required as protection from solar storm events and galactic radiation effects. Future GEO missions, including multipurpose platforms, will require a definition of shielding requirements and the means to achieve it if the role of man is considered essential to achieving mission objectives. There is growing interest in a return to the Moon to continue scientific studies of
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