Longitudinal Landing Control Law for an Autonomous Reentry Vehicle

This paper discusses the longitudinal ight-pathcontrol lawdesigned and  ight tested for theAutomaticLanding Flight Experiment (ALFLEX). ALFLEX, for which  ight tests were conducted in 1996, demonstrated Japanese potential for developing automatic landing technology for a reentry space vehicle. One of the critical factors in satisfying the design requirements for landing on a limited length runway was longitudinal  ight-path control following the pre are maneuver. Robustness against uncertainties and sensor errors is a key issue in longitudinal  ight-path control. The longitudinalguidance and control lawswere carefully designed and  ight tested. Although the  ight tests proved that the design satisŽ ed all landing requirements, it identiŽ ed critical parameters affecting landing performance such as vehicle longitudinal aerodynamics, navigation error, and air data sensor error. This paper describes data obtained during the development and  ight tests, as well as further investigations conducted after the  ight tests in order to improve landing performance for future space vehicle developments. In the subsequent design review a new approach called stochastic gain tuning was adopted, where the guidance feedback gain is tuned to maximize the probability of mission success. The results indicate some possibility of improvement of robustness.