Abstract
The tri-propellant engine is an attractive propulsion system for a near-term Single-Stage-to-Orbit (SSTO). This paper presents the results of an analytical study to determine the optimum fuel mass ratio of high-density kerosene and low-density liquid hydrogen for SSTO rockets. We performed flight simulation analyses to calculate payload capabilities for tri-propellant combinations with varying kerosene-hydrogen ratios, based on the current, matured Expendable Launch Vehicle's (ELV’s) technology both in propulsion and structural performance. A series burn was assumed for two cases of typical vehicle size; the same amount of total propellant mass and the same total impulse. The present study has shown that a tri-propellant combination with about 85% kerosene and 15% liquid hydrogen provides the highest vehicle performance. The trl-propellant SSTO performance gain at this optimum combination is about 800 m/s in vehicle velocity increase compared to a pure liquid oxygen/liquid hydrogen propulsion system. This performance gain is significant even if the increased complexities are taken into account for the tri-propellant propulsion system.
