STS. Grishin and Chekalin also point out the necessity of splitting the traffic into cargo and passenger missions. In connection with multi-stage vehicles he suggests the stages must be ‘returned'. Grishin and Chekalin also suggest that no parts of a high traffic flow transportation system must be left in orbit or use toxic propellants and in particular solid propellants should be avoided. Thus boosters should be liquid propellant, as these USSR literature sources strongly oppose solids on environmental grounds. We anticipate LOX/UDMH from past USSR technology and performance grounds. The only possible objection to UDMH is its mildly carcinogenic character and propane could be an alternative. The overall character of the discussions in the literature does indicate that the anticipation is for a heavy lifting vehicle based on conventional rockets to LEO, although airbreathing options are regarded as a future prospect having advantages from a reduced vehicle scale. A recent paper by Leonid Leskov in the journal Space Policy [9] also quotes Feoktistov's papers on masses and costs, although $165/kg is the specific cost quoted. At the IAF Congress in Lausanne in September 1984 Novikov and Scheverov [10] discussed the optimization of space transportation systems from an economic view point and in particular included the concepts of modernizations of existing systems, their unification with new ones, and a design approach using modular construction. This has been a subject of several papers at past IAF Conferences [11]. From USSR comments, the system will be fully recoverable, and involve about 50 vehicles in the fleet. From Sarkisjan (Fig. 6) this would be essentially complete by 1993 implying a production rate of about seven vehicles per year at least. The Timescales The programme timescale suggested by Sarkisjan and colleagues (Fig. 7) is apparently
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