6-DEGREE-OF-FREEDOM GUIDANCE AND CONTROL ANALYSIS OF MARS AEROCAPTURE

A six-degree-of-freedom (6DOF) simulation has been developed to invest igate the control and guidance issues of a Mars aerobraking vehicle. T he guidance algorithm used is a predictor-corrector guidance formulati on designed to control the exit orbital apoapsis and wedge angle using bank angle modulation. Major features of this predictor-corrector gui dance algorithm include 1) integration of the 3DOF equations of motion within an inner-loop simulation, 2) load-relief logic, 3) finite roll rates, and 4) an aerodynamic feedback multiplier. The algorithm has b een shown to be capable of successfully guiding the vehicle through co mbinations of atmospheric density dispersions, aerodynamic mispredicti ons, and off-nominal atmospheric interface conditions. This study demo nstrated that the addition of vehicle dynamics to the Mars aerobraking simulation does not significantly impact mission feasibility. That is , a good control system design coupled with an adaptive guidance algor ithm can ensure mission success (as measured by the required postaeroc apture propulsive maneuvers) in the presence of numerous off-nominal c onditions.