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

This study examined previously described Mars mission scenarios for the years 2014, 2016, 2018, and 2020 for vehicles using aerobraking (AB), nuclear thermal propulsion (NTP), and a combination of the two technologies. Each launch opportunity evaluated allowed for a nominal, long-duration (similar to 600 day) surface stay, a mission abort after a short surface stay (10 to 65 days), and a swingby abort with no Mars landing. The initial mass required in low Earth orbit (IMLEO) for the spacecraft to be able to execute any of these three options was determined for each combination of launch year and vehicle design (chemical propulsion with aerobraking (CHEM/AB), NTP and NTP/AB). The principal findings of the investigation were: 1) Viable mission abort opportunities exist for vehicles that use chemical propulsion with aerobraking without exceeding 1000 metric tons. 2) In most cases, these abort strategies do not cause atmospheric entry velocities to exceed previously recommended limits for the aerocapture of low lift to drag ratio (L/D) vehicles. The exceptions are minor and possibly could be eliminated with further manipulation of mission dates. 3) Significant reductions in IMLEO occur when vehicles which use nuclear propulsion employ aerobraking for the Mars orbit insertion; on average, a specific impulse (I-sp) of 1100 seconds (corresponding to advanced technology NTP) would be required for all-propulsive designs to match the IMLEO of systems which use present technology NTP (I-sp = 825 s) in conjunction with aerobraking at Mars.