1 The Use of Energy - State Analysis on a Generic Airbreathing Hypersonic Vehicle

A possible next-generation launch vehicle may be a fully reusable, single-stage-to-orbit (SSTO) aerospacecraft. This class of hypersonic vehicle includes highly integrated airframe and propulsion systems, hence fuel-optimal trajectories are of special interest. Also, since 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 justified 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 justified when the system dynamics exhibit multitime-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 to a full dynamic solution obtained using a non-linear 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 justified for the class of vehicle in question, at least for obtaining rapid performance estimates, as well as gaining insight into the basic performance issues. * Professor of Aerospace Engineering and Director. Associate Fellow AIAA. ** Visiting Graduate Research Assistant. Formerly with the Technical University of Stuttgart. Student Member AIAA. Copyright © 1997 by David K. Schmidt. Published by the American Institude of Aeronautics and Astronautics with permission.