Earth aerobraking strategies for manned return from Mars

Earth-return entry corridor analyses are performed to evaluate the atmospheric flight environment of manned return from Mars. Trajectory and performance differences between aerocapture and direct entry are assessed and quantified in terms of the required aerobrake lift-drag ratio (L/D), stagnation-point heating, and the significance of off-nominal atmospheric conditions. The Earth-return aerobraking scenarios compared are 1) aerocapture into a phasing orbit with a 24-h period, 2) aerocapture into a 500-km circular orbit, 3) and direct entry to splashdown. No significant differences between aerocapture to a 500-km circular orbit and direct entry were observed in terms of aerobrake L /D requirements, maximum deceleration, or peak stagnation-point heat rate. The importance of parking orbit selection is demonstrated for low entry velocity Earth-return missions from Mars and missions returning from the Moon. Additionally, a stagnation-point heating analysis revealed that in all cases the peak heat rate is large enough to require an ablative thermal protection system for manned return from Mars. However, for entry velocities of 12.5 km/s and less, the heating environment is of the same order of magnitude as that experienced during the Apollo program. To perform the entry analysis, two predictor-corrector guidance design strategies were developed. Use of a predictor-corrector technique was shown to provide adequate flight margin for managing off-nominal atmospheric conditions.

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