FLEXIBLE STRATEGIES FOR MANNED MARS MISSIONS USING AEROBRAKING AND NUCLEAR THERMAL PROPULSION

This study examined previously described Mars mission scenarios for th e years 2014, 2016, 2018, and 2020 for vehicles using aerobraking (AB) , nuclear thermal propulsion (NTP), and a combination of the two techn ologies. Each launch opportunity evaluated allowed for a nominal, long -duration (similar to 600 day) surface stay, a mission abort after a s hort surface stay (10 to 65 days), and a swingby abort with no Mars la nding. The initial mass required in low Earth orbit (IMLEO) for the sp acecraft to be able to execute any of these three options was determin ed for each combination of launch year and vehicle design (chemical pr opulsion with aerobraking (CHEM/AB), NTP and NTP/AB). The principal fi ndings of the investigation were: 1) Viable mission abort opportunitie s exist for vehicles that use chemical propulsion with aerobraking wit hout exceeding 1000 metric tons. 2) In most cases, these abort strateg ies do not cause atmospheric entry velocities to exceed previously rec ommended limits for the aerocapture of low lift to drag ratio (L/D) ve hicles. The exceptions are minor and possibly could be eliminated with further manipulation of mission dates. 3) Significant reductions in I MLEO occur when vehicles which use nuclear propulsion employ aerobraki ng for the Mars orbit insertion; on average, a specific impulse (I-sp) of 1100 seconds (corresponding to advanced technology NTP) would be r equired for all-propulsive designs to match the IMLEO of systems which use present technology NTP (I-sp = 825 s) in conjunction with aerobra king at Mars.