Fig. 22. POTV configuration. Fig. 23. SPS evolutionary development plan elements. 0.526x 106 kg of payload. This concept uses argon electric thrusters for thrusting and attitude control. The solar array, which provides power for the thrusters, is a single bay section of the gallium arsenide (GaAs) SPS concept. Because of the selfannealing characteristics of GaAs cells, it can traverse the radiation belt with potentially no degradation of the cells. The POTV concept and its characteristics are shown in Fig. 22. This concept uses a single stage which is propelled by LO2/LH2 rocket engines. The stage is refueled at GEO for the return trip to LEO. The propellants are carried to GEO on the EOTV. Program planning An end-to-end definition of the SPS program was conducted. The major phases are shown in Fig. 23, which also shows the dates when major system elements are introduced. Major emphasis was placed on the definition of near-term technology development programs. Detailed programs were defined for the GaAs solar array, power distribution and control, the microwave transmission system, and the transportation system.
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