Electric propulsion options for Mars cargo missions

Abstract

This paper summarizes an evaluation of mission performance (in terms of vehicle mass and trip time) of solar electric propulsion (SEP) and nuclear electric propulsion (NEP) operating at power levels on the order of 1.5 MWe for Mars cargo missions. The SEP and NEP vehicles are both assumed to use lithium-propellant magnetoplasmadynamic (MPD) thrusters with an efficiency (electric-to-jet) of 60% at a nominal specific impulse of 5000 lbf-s/lbm (49 kN-s/kg); the propellant tankage factor is assumed to be 2.8%. The SEP system has a total power, power conditioning, and propulsion system specific mass of 13.6 kg/kWe with a power conditioning system efficiency of 89.6%. The NEP power system uses an SP-100 reactor with dynamic power conversion (Rankine). Two technology levels were considered for the nuclear-electric power system; the baseline system employs refractory-metals components consistent with the nominal SP-100 design. This system has a total power, power conditioning, and propulsion system specific mass of 24.8 kg/kWe with a power conditioning system efficiency of 90.2%. The second nuclear-electric power system operates at a lower temperature to allow the use of non-refractory metals components; this system has a total system specific mass of 48.0 kg/kWe (with the same power conditioning system efficiency as the refractory-metals system). The baseline refractory-metals NEP system has a lower initial mass in low Earth orbit (IMLEO) and shorter trip time than the non-refractory NEP system, but the non-refractory NEP system has a * Technical Group Leader, Advanced Propulsion Technology Group; Member AIAA. t Senior Staff Scientist, Advanced Planning. potential cost and schedule advantage over the refractory-NEP system because refractory metals need not be developed and tested. At a given bus power level, the SEP system has a somewhat lower IMLEO and longer trip time (due in part to the reduction in power as the SEP vehicle moves away from the sun) as compared to the refractory-metals NEP system. Interestingly, if the total bus power level of the SEP system is increased to give it an IMLEO comparable to that of the refractory-metals NEP system, the SEP system can have a shorter trip time, reflecting the benefit of the lower total system specific mass of the SEP system.