The concept of a low thrust solar electric propulsion stage using mercury propellant was employed, as directed, in the transportation related investigations. In recognition of the importance of the time value of money invested in the payload it is important to consider this factor in future transportation system tradeoff investigations. Mercury pollution to the extent indicated for the operational system would not be accestable and further transportation system investigations must include other propellants. A risk factor of 4 should apply not only currently but on into the late 70's to early 80's due to a probable delay in the decision process, whereby high performance, low cost, low to geosynchronous orbit transportation would be justified only by a firm commitment to the power from space program. It is anticipated that SEPS would not be in use, rather be in development, in the mid 80's so that large scale pre-prototype flight test demonstrations in that time period would be confined to low earth orbit which is probably acceptable. It would be desirable to have the fully operational SEPS for the early phases of prototype transportation to geosynchronous orbit and mandatory to have it for the completion of the prototype to a complete operational system. Transportation operations which are functions of shuttle are in development and may be adequate for conducting program development up through pre-prototype flight test demonstration. Whether or not satellite power system development or operational payloads should impact the shuttle concepts must be the subject of payload investigations. How the tranportation operations as well as the vehicles (SEPS & HLLV) themselves may effect the orbital microwave system technologies and vice versa will become known only as in depth investigations of payload and transportation are conducted in parallel. A risk rating of 4 should apply.
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