A mercury propellant, electron-bombardment ion propulsion system with a solar cell power source is assumed to have the following characteristics: Overall system efficiencies of 0.7 are equaled or exceeded with today's technology. The overall system specific weight assumption is based on an assumed power supply and conditioning specific weight of 5 Ibm/kw, in line with projected solar cell weights for the SSPS itself, and propellant tankage, feed, thruster, structure, etc., specific weight of 10 lbm/kw. Current values for overall system specific weight fall in the range of 65-150 Ibm/kw; however, the assumed value of 15 has precedence in literature (Ref 21). The SSPS ion propulsion system, therefore, has a value of . It can now be determined from Fig. 3.1-14 and 3.1-15 that: An ion propulsion system can be sized for a SSPS delivery to geosynchronous orbit from the candidate 7000 n mi assembly altitude. The method followed is identical to that outlined in Subsection 3.1.4.1. The mission parameters assumed are:
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