ORBITAL TRANSFER SYSTEMS FOR LUNAR MISSIONS

For future Lunar mission operations basically two types of transfer systems can be conceived (a) the conventional direct-injection expendable vehicle approach, and (b) the re-usable orbit-to-orbit (LEO-LLO-LEO round-trip system. The second solution has been studied in Europe in the SPACE TUG Phase A Study in 1971172 for NASA as a fully reusable system and this is compared to a more recent NASA-MSFC transfer vehicle concept with expendable propellant tanks and aerobraking. The results of an analysis on mission opportunities for LEO-LLO transfers is presented. A European option is also shown for mode (a), using the ARIANE 5 for lunar missions with an optimized cryogenic transfer vehicle, derived from the H.10 Stage (ARIANE 4) plus a lunar vehicle derived from the MMII-CRAF propulsion module using the 27.5 kN engine from the ARIANE L.9 Stage which could land a 3.4 ton vehicle on the lunar surface. Finally a completely new option (c) is discussed: the use of a ballistic SSTO vehicle for lunar landing missions after refuelling in LEO. This seems to be a highly effective single transportation element approach compared to the seven elements SATURN V-APOLLO-LM system of the 60ies,