Abstract
Under the Mars Transportation Assessment Study, NASA and the U.S. Department of Energy are performing analyses and generating concepts for crewed nuclear electric propulsion (NEP) missions to Mars. This paper presents the results of trade studies and concept development for the nuclear electric power system, consisting of the fission reactor, radiation shielding, power conversion, heat rejection, and power management and distribution (PMAD). The nuclear power team completed trade studies to evaluate different reactor and power conversion technologies and developed preliminary concepts for the crew shielding, waste heat radiators, and PMAD. The initial results suggest that a modified terrestrial microreactor combined with supercritical CO2 Brayton conversion could be used to perform the crew and cargo missions with satisfactory performance and modest risk. The paper includes preliminary development strategies that could bring the NEP technology to fruition for Mars missions in the late 2030s or early 2040s.
| Original language | English |
|---|---|
| Pages (from-to) | S52-S66 |
| Journal | Nuclear Technology |
| Volume | 208 |
| Issue number | sup1 |
| DOIs | |
| State | Published - 2022 |
Funding
Mission studies conducted by the NASA Glenn Research Center (GRC) COMPASS Team identified the need for a 1.9-MW(electric) power system to perform a 2-year round-trip crewed mission to Mars using a hybrid nuclear electric propulsion (NEP) and chemical propulsion vehicle, as shown in Fig. 1 (Ref. 1). The chemical stage uses two 15-klbf liquid oxygen and liquid methane (LOX/LCH4) engines to perform the high-thrust burns at Earth departure, Mars capture, and Mars departure. The NEP stage performs the interplanetary transfers and Earth capture. The COMPASS studies evaluated multiple crewed mission opportunities spanning 2035 to 2042 that utilize (1) a low Earth orbit (LEO) aggregation orbit, (2) an uncrewed LEO–to–near rectilinear halo orbit spiral where the NEP vehicle rendezvous with the deep-space crew habitat, and (3) a 760-day opposition-type round-trip mission that includes a 30-day Mars stay. Additional mission analysis indicated that a duplicate NEP stage, using the same 1.9-MW(electric) nuclear power system and electric propulsion (EP) thrusters—but without the chemical stage—could perform precursor cargo missions delivering payloads of about 200 t to Mars after a LEO spiral and 535-day one-way Mars trip.Fig. 1. Hybrid NEP and chemical propulsion vehicle concept. Hybrid NEP and chemical propulsion vehicle concept. The COMPASS study mission design results are summarized in Table I. The mission studies considered crewed opposition missions in 2035, 2039, and 2042 using the same NEP and LOX/LCH4 propulsion elements. That vehicle uses a 1.8-MW(electric) array of EP thrusters [leaving 100 kW(electric) for vehicle housekeeping loads] with a specific impulse of 2600 s to deliver the 45-t crew habitat to Mars and return the crew to Earth in 760 days. The Xe and LOX/LCH4 propellant loads vary across the opportunities, but all the missions can be accomplished using a combination of two Space Launch System (SLS) launch and five Super Heavy commercial launch vehicle (CLV) (e.g., Starship) fuel deliveries. The COMPASS team also evaluated 2035 and 2039 crewed conjunction missions that exceed the 2-year mission goal but increase the crew time at Mars from 40 to 300 days and decrease the Earth launch fleet. The final case shows an all-NEP cargo conjunction mission that can deliver up to 195 t to Mars in 535 days using a duplicate NEP stage as the one envisioned for the crew mission with only one SLS and one Super Heavy CLV tanker.Table I Compass Mission Design Cases*2035 Opposition2039 Opposition2042 Opposition2035 Crew Conjunction2039 Crew Conjunction2037 Cargo ConjunctionTotal trip time (day)76076076010581047535 (one-way)Power to EP [MW(electric)]1.81.81.81.81.81.8Specific impulse (s)260026002600260026002600Mars parking orbit stay time (day)404040300300N/Aa Dry NEP stage (t)757575757575Payload mass (t)45454545453 × 65Usable Xe (t)131124122596081Usable LOX/LCH4 (t)13918718025380Earth departure mass (t)418460448226240346Number of launches for NEP/chemical stage2 SLS + 5 Starships1 SLS + 2 Starships1 SLS + 1 Starship* All cases assume 1200 K LEU reactor with SCO2 Brayton conversion, 20 × 100-kW(electric) Hall thrusters, lunar distant high earth orbit crew departure, and 2-sol Mars parking orbit. aN/A = not applicable. Compass Mission Design Cases* * All cases assume 1200 K LEU reactor with SCO2 Brayton conversion, 20 × 100-kW(electric) Hall thrusters, lunar distant high earth orbit crew departure, and 2-sol Mars parking orbit. aN/A = not applicable.
Keywords
- Brayton conversion
- Human Mars mission
- nuclear electric propulsion
- space reactor