Nonlinear drag-tracking control applied to optimal low-lift reentry guidance

Abstract

A nonlinear reentry control system to track a drag reference trajectory is presented. The control system is based on feedback linearization of the drag dynamics and a linear control law with constant gains to shape the drag error dynamics. Input to the control system is a smooth drag-vs-velocity profile; all other reference commands are generated by a generic guidance-control interface. The control system is simulated on a variety of drag reference profiles that are obtained by off-line trajectory optimization. Despite large variations in profile shape and nominal downrange, the same control system design demonstrates uniform tracking performance in all simulated cases while subject to significant atmospheric disturbances and drag rate estimation errors. (AIAA).A nonlinear reentry control system to track a drag reference trajectory is presented. The control system is based on feedback linearization of the drag dynamics and a linear control law with constant gains to shape the drag error dynamics. Input to the control system is a smooth drag-vs-velocity profile, all other reference commands are generated by a generic guidance-control interface. The control system is simulated on a variety of drag reference profiles that are obtained by off-line trajectory optimization. Despite large variations in profile shape and nominal downrange, the same control system design demonstrates uniform tracking performance in all simulated cases while subject to significant atmospheric disturbances and drag rate estimation errors.

Skip Entry Trajectory Planning and Guidance

“…For low lifting vehicles, various other methods have been suggested for atmospheric guidance. For direct entry, one method is to extend the Space Shuttle entry guidance approach to track a pre-computed drag profile [14,15,16,17,18]. Modern computer capabilities permit generation of a feasible trajectory onboard the vehicle and use of a similar Shuttle-like tracking technique [27].…”

Adaptive on-board guidance for entry vehicles

“…The detailed control law design has been shown in a previous paper. 17 Given the navigated energy e, the trajectory command polynomial (14) provides the range-rate command and its derivatives with respect to energy given by The dash indicates differentiation with respect to energy. The range-rate commands are converted to the commanded drag acceleration and its derivatives with respect to time which represent the controlled variables in the trajectory control loop.…”

“…The control law design, which has been published in a previous paper, 17 is based on feedback linearization of the drag dynamics and provides uniform tracking performance from atmospheric entry to target conditions. For the design, information on a nominal trajectory is unnecessary.…”

Skip entry trajectory planning and guidance

“…For low lifting vehicles, various other methods have been suggested for atmospheric guidance. For direct entry, one method is to extend the Space Shuttle entry guidance approach to track a pre-computed drag profile [14,15,16,17,18]. Modern computer capabilities permit generation of a feasible trajectory onboard the vehicle and use of a similar Shuttle-like tracking technique [27].…”