Longitudinal landing control law for an autonomous reentry vehicle

This paper discusses the longitudinal flight-path control law designed and flight tested for the Automatic Landing Flight Experiment (ALFLEX). ALFLEX, for which flight 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 flight-path control following the preflare maneuver. Robustness against uncertainties and sensor errors is a key issue in longitudinal flight-path control. The longitudinal guidance and control laws were carefully designed and flight tested. Although the flight tests proved that the design satisfied all landing requirements, it identified 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 flight tests, as well as further investigations conducted after the flight 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.