plants per year. The most recent estimates indicate about 60 to 100 flights per station using an HLLV; hence, development of an HLLV is a critical item as cited by most studies (for instance, Ref. A2, A4 and All) . (2) Status and Proposed Development Procedures All approaches, i.e., solar-thermal, solar-photovoltaic and PRS, would begin development activities by utilizing the Space Shuttle. Several divergent approaches are under consideration for the following stages. One of these involves a "shuttle derivative" (Ref. All and A14) for transport in the construction of a 1 GW pilot plant, followed by use of the HLLV for the 5 GW operational plant. The "shuttle derivative" would also be used in the development of the PRS (Ref. A14). Other approaches proceed more directly from the Shuttle to some form of an HLLV, although one report (Ref. E9) states that a "growth shuttle" could provide personnel transport, and another (Ref. A9) that a "growth shuttle" could transport high priority equipment and tools as well as personnel. The HLLV envisioned by various contractors varies somewhat. Of the documents discussing it, Ref. E9 describes it as a fully reusable "space freighter" with a 500,000 pound (225,000 kg) payload capacity; Ref. A9 describes it as a fully reusable vehicle with the same capacity, but does not detail it further. Reference A4 describes it as a "Reusable-Runway Recovered Space Transporter" with a payload capacity of only 77,000 pounds (35,000 kg). In general, details of the HLLV beyond those summarized above were found to be scanty. For the solar-photovoltaic SSPS, Ref. All discusses "near term" studies, where "near term" is defined as "up to the time the Space Shuttle will be available for hardware flight testing." With respect to Launch Systems, these near term studies are outlined as follows: • Trade-off total system cost to achieve a fully recoverable launch vehicle versus more payload and reduced recove rabi1i ty. • Evaluate impact of launch site operations on launch vehicle size selection.
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