Use of Energy-State Analysis on a Generic Air-Breathing Hypersonic Vehicle

Abstract

Apossiblenext-generation launch vehiclemaybea fullyreusable,single-stage-to-orbitaerospacecraft.Thisclass of hypersonic vehicle includes highly integrated airframe and propulsion systems; hence fuel-optimal trajectories are of special interest. Also, because these vehicles are neither conventional aircraft nor rockets, the appropriate approach for trajectory analysis during preliminary design, for example, is of interest. Addressed here is whether the energy-state method is justie ed for the determination of such trajectories for scramjet-powered, hypersonic vehicles. The focus is on the scramjet-powered phase of the mission. The energy-state approach is known to be justie ed when the system dynamics exhibit multi-time-scale behavior, and such behavior is shown to exist for the vehicle and mission phase under investigation here. Furthermore, solutions obtained via the energy-state assumption are compared with a full dynamic solution obtained using a nonlinear programming routine. It is shown that the results from the two methods are in reasonably good agreement. On the basis of these results, the energy-state method would appear justie ed for the class of vehicle in question, at least for obtaining rapid performance estimates, as well as gaining insight into the basic performance issues.