the following paragraphs, the activities, plans, and requirements for developing what is often referred to as the Heavy Lift Launch Vehicle (HLLV) are summarized, first in terms of transportation requirements, followed by status and proposed development procedures, then by a summing-up of the overall area. (1) Transportation Requirements The overriding transportation requirement is the massive amount of hardware and material that must be placed into orbit. Estimates of weights for the solar-photovoltaic power station range from 23 million pounds (10.5 x 10 kg) (Ref. A4) , to 40 million pounds (18 x 10 kg) (Ref. All). For solar thermal approaches, the estimates range from 100 million pounds (46.4 x 10$ kg) (turbogenerator approach, Ref. A4), to 220 to 440 million pounds (100 to 200 x 10 kg) (solar-Brayton and solar thermionic, Ref. E9) to about 770 million pounds (350 x 10 kg) (nuclear-Brayton, Ref. E9). Weight estimates for the Power Relay Satellite (PRS), while less, are still large. They range from 500,000 pounds (0.23 x 10 kg) (Ref. A4) to 925,000 pounds (0.42 x 10 kg) (Ref. All). In addition, maintaining the propellant supply for attitude control and stationkeeping for all approaches imposes transportation requirements. One estimate, for instance, of propellant needs for a 5 GWe SSPS is ap- 3 proximately 30,000 pounds (14 x 10 kg) per year (Ref. A2). Besides the transportation requirements for material and supplies, personnel must be transported for assembly and construction activities. Also, the volume as well as the weight capacity of the launch vehicle payload bay will play an important role since much of the material is expected to be lightweight but bulky. Based on all these requirements, several contractors have estimated the number of flights required. These estimates are strongly a factor of the implementation approach and thus vary widely. One estimate for constructing an operational solar- photovoltaic SPS system is more than 500 flights per year (Ref. A2); an estimate for constructing a solar-thermal plant is 30 flights (Ref. E9). Also, it is estimated (Ref. F2) that 50 Space Shuttle transport vehicles, each flying once every day, would be required to build 10 space-based
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