AIRBREATHING ENGINE SELECTION CRITERIA FOR SSTB PROPULSION SYSTEM

This paper presents airbreathing engine selection criteria to be appli ed to the propulsion system of a Single Stage To Orbit (SSTO). To esta blish the criteria, a relation among three major parameters, i.e., del ta-V capability, weight penalty and effective specific impulse of the engine subsystem, is derived as compared to these parameters of the LH 2/LOX rocket engine. The effective specific impulse is a function of t he engine I-sp and vehicle thrust-to-drag ratio which is approximated by a function of the vehicle velocity. The weight penalty includes the engine dry weight, cooling subsystem weight. The delta-V capability i s defined by the velocity region starting from the minimum operating v elocity up to the maximum velocity. The vehicle feasibility is investi gated in terms of the structural and propellant weights, which require s an iteration process adjusting the system parameters. The system par ameters are computed by iteration based on the Newton-Raphson method. It has been concluded that performance in the higher velocity region i s extremely important so that the airbreathing engines are required to operate beyond the velocity equivalent to the rocket engine exhaust v elocity (approximately 4,500 (m/s)).