MODEL-BASED GUIDANCE AND CONTROL FOR ATMOSPHERIC GUIDED ENTRY

The paper describes a reference path-tracking algorithm for the compensation of atmospheric and aerodynamic dispersion during the atmospheric entry of a low lift-to-drag interplanetary vehicle. The paper focuses on the longitudinal control. Lateral control is briefly mentioned. Attitude control has been presented elsewhere. The algorithm follows the Embedded Model Control methodology and is based on the real-time estimation and cancellation of the causes that stray the vehicle path from the reference trajectory. The real-time control modulates the vertical component of the lift in order to drive the vehicle fourth-order longitudinal dynamics. To simplify the control structure, longitudinal dynamics is decomposed in a series of two second-order dynamics. The upstairs dynamics (flight path angle and altitude) is commanded by the lift vertical component, the downstairs dynamics (velocity and downrange) is driven by altitude modulation. Arranging the control algorithm in a hierarchical manner becomes straightforward. Control algorithms have been tested by Monte Carlo simulations on a high fidelity six degrees-of-freedom simulator showing that the control approach provides acceptable residual dispersion at the parachute deployment point.