Fuel Trade Study for a Nanosat Launch Vehicle Upper Stage

Abstract

This paper discusses the trade study between three different cryogenic/cooled hydrocarbon fuels, methane, propane, and propylene, for use on a nanosat launch vehicle (NLV) upper stage with the capability of lifting very small payloads (< 10 kg) to low earth orbit. Liquid oxygen (LOX) is used as the oxidizer for all fuel options. All three propulsion systems use regulated pressure with heated gaseous helium and transition to a blow-down phase so that when all fuel is expended, the chamber pressure is at 50% of the nominal engine chamber pressure. The transition point occurs when 66% of the fuel has been used for all three fuel systems. Tank sizes and masses are determined based on state-of-the-art cryogenic composite and aluminum propellant tanks, and COPVs for pressurants. Chilled propylene is shown to be the most suitable propellant selection. For the nominal 10 kg payload mission analyzed in this study, it allows a 4% increase in payload mass over LOX/propane option and an 11% increase of payload mass over LOX/methane. This improvement comes from a greater density-Isp which leads to slightly smaller propellant tanks and reduced helium requirements.