SPACE TRANSPORTATION The space transportation and operations challenge that must be met to make the Powersat system practical is symbolized here. Transportation to low Earth orbit must attain recurring cost figures in the range of $20 per pound of useful payload, requiring development of a large reusable freighter vehicle. Payload capability on the order of 500,000 pounds will be needed with low- density payloads. Launch rate will be one to several per day. The power satellites themselves, because of their very large size and lightweight structure, must be assembled in space. The present baseline calls for assembly in low orbit, but the relative merits of low orbit versus high orbit assembly are still under evaluation. The satellite modules or subassemblies must be moved to geosynchronous orbit, requiring a high efficiency, low cost orbit transfer system. Preliminary studies indicate that the power generation capability of the satellite modules can be used to effect the orbit transfer by using part of the satellite output to power electric rocket tugs. This method of transfer can attain the low-cost, high- efficiency goals.
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