Reentry Flight Controller Design Using Nonlinear Dynamic Inversion

Abstract

The application of nonlinear dynamic inversion to the design of a e ight controller for atmospheric reentry is discussed. Nonlineardynamic inversion is used due to thelarge e ight envelopethat characterizes thereentry of the small wingless lifting body vehicle. Moreover, the increased computational capability of modern e ight computers, as well as the mission requirements of crew return vehicles, supports the application of a nonlinear control law. The control design is based on nonlinear/linear inversion of the vehicle model and is divided in three phases: nonlinear inversion of the vehicle’ s dynamics, linearization and linear inversion of the aerodynamic database, and actuator allocation. The vehicle’ s dynamics were inverted assuming timescale separation between attitude and attitude rates. The assignment of the vehicle’ s actuators was scheduled against dynamic pressure, accounting for the efe ciency of each actuator on the different phases of e ight. Input ‐output linearization was performed for the phase of e ight where only two actuators were available. The correctness of the controller and its performance are evaluated with numerical simulations of two different entry trajectories.