Earth-orbit masses for five-impulse Mars stopover missions in 1980.

Abstract

Fourand 5-impulse trajectories for manned Mars stopover missions are compared with respect to initial mass in Earth orbit (IMEO) to determine the advantages or disadvantages associated with the use of 3-impulse outbound or inbound segments. The 3-impulse trajectory segments are generated using an analogy between the primer vector on a low-thrust transfer and the corresponding impulse-thrust transfer. The results obtained apply specifically to Mars missions in the 1980 time period with an Earth entry speed of 60,000 fps. It was found that, relative to the absolute optimum 4-impulse (2 + 2) Mars mission in the 1980 opposition, no reductions in IMEO can be realized by employing intermediate impulses. However, large reductions in IMEO for off-optimal 4-impulse missions can be realized by employing intermediate impulses on the outbound segment of the missions. The heliocentric Earth launch window for the 1980 opposition can be increased by 300 days for a 40% penalty in IMEO. Although a reduction of round-trip characteristic velocity can be demonstrated when intermediate impulses are employed on the return segments of Mars missions, no reductions in IMEO could be shown for the assumed entry speed.