Two configurations of the independent electric COTV have been synthesized and are currently under investigation. Both COTV configurations are large, lightweight structures constructed in LEO and are associated with an al 1-GEO SPS construction mode. The first concept utilizes a self-annealing gallium aluminum arsenide array with a concentration ratio of 2 and carries a payload of 4000 MT for a LEO-GEO trip time of 133 days and a total round trip time of less than 180 days. Ion bombardment thrusters of 100 cm diameter are used with an Isp of 13,000 seconds and argon as the working fluid. The concept is shown on Figure A-23. The primary thruster array of 259 thrusters is suspended by cables and located at the vehicle c.g. Additional attitude thruster control packages are located at the structural extremities. The component mass breakdown is given in Table A-4. The second concept utilizes a silicon photovoltaic solar array in a planar configuration with no concentration reflectors. Round trip time from LEO-GEO-LEO is approximately 160 days which also allows two trips per year for each COTV. Ion bombardment thrusters of 120 cm diameter are used with an Isp of 7,000 seconds and argon as the working fluid. The concept is shown on Figure A-24. Thruster modules of 296 electric thrusters each and an appropriate number of chemical thrusters are located at the four corners of the COTV. The component mass breakdown is given in Table A-5. The COTV startburn mass is seen as 2085 MT for the second concept as compared to 1442 MT for the first concept of the independent electric COTV. The cost effectiveness of both configurations is quite sensitive to items which have very little data base such as maintenance/refurbishment requirements, design life of various components and unit cost. Both electric approaches have their advantages--the self-powered requiring less HLLV flights and the independent minimizing the damage to SPS solar cells while traversing the Van Allen belts. The cost comparison of the two approaches is difficult to assess due to the lack of data base. The relative advantages and disadvantages of conducting construction operations in LEO vs GEO have been explored, and GEO construction has been selected for
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