Comparison of Propulsion Options for a Lunar Lander Ascent Stage

The propulsion system for the ascent stage of a lunar lander will be required to meet some unusual requirements, including extreme thermal environments and difficult safety objectives. This paper presents the results of an initial study of candidate propulsion options for the ascent stage. The study considered pump-fed and pressure-fed engines using eight propellant types: LOX/hydrogen, LOX/methane, LOX/ethanol, LOX/kerosene, LOX/monomethyl hydrazine (MMH), LOX/silane, nitrogen tetroxide/MMH, and chlorine pentafluoride/hydrazine. The delta-V and thrust to weight requirements for the stage were determined via trajectory simulation. Thermal analysis determined that passive storage of liquid hydrogen and oxygen is feasible for mission durations of a few months. A trade study comparison concluded that pump-fed engines were preferred over pressure-fed engines, and that LOX/LH 2, LOX/ethanol, and N2O4/MMH were the most promising propellant options. Silane and chlorine pentafluoride were found to be impractical, with few desirable systemlevel characteristics and do not merit further consideration.