It should be pointed out that this hybrid transfer does not include a AV for circularization at the apogee of the Hohmann transfer. The spacecraft will thus cross the Van Allen Belts at perigee. It is assumed that the speed at this location will be high enough to avoid any serious degradation. Furthermore the on board electronics could be, to a large extend, be powered off to avoid potential latch-up phenomena. Structural weight for tanks and main engine is rounded to 4% (usual value is 10%, but we assume a better value due to use of Al Li alloy) of the total mass of fuel. The result of these mass estimates are provided in the summary below. Under those assumptions the total mass for 20309 km is: 172.3 t (near term) and 77.61 (far term). Table 10.4.3 Mass Summary For Structure Those masses are worst case values, as for GEO the lighter antenna save around 101. Nevertheless, due to the uncertainties for this estimate, a gain of 101 does not change dramatically any conclusion. Recommendations and Critical Issues Engineering Aspects After this brief description the main critical issues from a technological standpoint are; • Development of efficient amplifiers and oscillators at 35 GHz, mainly in the family of gyrotrons. • Development of phase shifters for phase adjustment of the sources of the antenna. • Development of electrical thrusters, both for attitude control and transfer.
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