Synopsis
The Mars Transportation Assessment Study (MTAS) evaluated nuclear thermal propulsion (NTP) and nuclear electric propulsion (NEP) for human Mars missions.
- The study found NEP enables lower total initial mass in low Earth orbit (IMLEO) compared to NTP, with 678 mt IMLEO for NEP/Chemical propulsion versus 934 mt for NTP. However, NTP enables faster transit times of around 2.5 years for the first mission elements versus around 3 years for NEP.
- The NTP reference vehicle uses four 25 klbf NTP engines with a specific impulse of 900 seconds. The engines use a graphite matrix reactor design with a 15 year lifetime. Hydrogen propellant tanks are sized for the round trip mission.
- The NEP reference vehicle uses a 1 MWe fission reactor power system with eight 120 kW Hall thrusters, 50 kV power processing units, and xenon propellant tanks sized for the round trip. The NEP thrusters have a specific impulse of 5000 seconds.
- A key advantage of NEP is it can leverage technology development from recent NASA electric propulsion efforts like the Asteroid Redirect Mission and Psyche mission. The NTP engines would require more significant technology maturation.
- The NTP engines pose greater terrestrial safety concerns due to the open cycle design and resulting engine exhaust products. In contrast, NEP only vents pure xenon which is inert.
- For the 2035 Mars conjunction opportunity, the NTP transit habitat launches on a single 130 mt-class SLS Block 2B. The NEP transit habitat launches on two 105 mt-class SLS Block 1B launches.
- For NEP, pre-deployment of the cargo vehicle 1-3 years ahead of the crew is necessary to enable the longer trip times. The NTP crew vehicle does a direct transit.
- Each option requires assembly in low Earth orbit and aggregation of propellant launched on commercial launch vehicles.
- NEP offers some abort options during Earth departure by thrusting back towards Earth. NTP offers more abort options during trans Mars injection.
- NEP uses aerocapture at Mars while NTP uses propulsive capture.
- NEP offers some robustness advantages compared to NTP. NEP provides consistent transit times across Mars opportunities.
- Overall, both NTP and NEP are viable options for human Mars missions, with NTP providing faster trip times while NEP offers some robustness and technology development advantages. Further analyses on partial power abort options for NEP and detailed mass breakdowns are recommended.