OPTIMALITY OF THE HEATING-RATE-CONSTRAINED AEROCRUISE MANEUVER

A synergetic maneuver can accomplish orbital plane changes with less f uel than an exoatmospheric maneuver. During the atmospheric pass, the spacecraft is subjected to very high heating rates, and any extra ther mal protection required may offset the fuel savings. A heating-rate-co nstrained synergetic maneuver called aerocruise has been widely studie d as a means for lowering the weight of the thermal protection system. We question the optimality of the aerocruise maneuver by considering the necessary and sufficient condition for a trajectory to remain on t he heating-rate boundary. By replacing the aerocruise-powered turn by a maximum thrust maneuver that we call aerobang, a perturbed synergeti c maneuver is obtained. This maneuver is compared against the numerica lly optimized aerocruise maneuver for the entry research vehicle. The results demonstrate that the aerobang maneuver consistently yields imp roved performance, i.e., inclination change per fuel mass, over the ae rocruise maneuver by as much as 14%. This result indicates that the op timal synergetic maneuver is yet to be determined and could very well be more complicated than a simple aerocruise turn.