Attitude Control System Design for Return of the Kistler K1 Orbital Vehicle

An attitude control system design is presented that provides the maneuver capability and aerodynamic angle maintenance necessary for the atmospheric reentry and return to launch site of an unmanned reusable launch vehicle. The primary functions are categorized into those that perform bank maneuver about the air-relative velocity vector and those that are responsible for the tracking and control of the vehicle aerodynamic trim conditions. The control system is supported by an onboard aerodynamic estimation function. The estimator uses measurement of vehicle states from navigation in combination with analytic models in a gain-scheduled filter environment to provide control with current trim angle information. The control system uses this information to minimize actual vehicle deviations from the trim. Also, control is provided with bank commands from a guidance function. As this paper is concerned only with the control and estimation functions, the guidance strategies are discussed only to the extent that is necessary to justify /clarify control or estimator designs. The algorithms developed here are applied to the Kistler K1 Orbital Vehicle and tested in the Kistler Integrated Vehicle Simulation at Draper Laboratory. Results indicate that the approach to entry/return control is both fuel efficient and effective from a landing accuracy perspective.