Six-degree-of-freedom guidance and control analysis of Mars aerocapture

A six-degree-of-freedom (6DOF) simulation has been developed to investigate the control and guidance issues of a Mars aerobraking vehicle. The guidance algorithm used is a predictor-corrector guidance formulation designed to control the exit orbital apoapsis and wedge angle using bank angle modulation. Major features of this predictor-corrector guidance 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 been shown to be capable of successfully guiding the vehicle through combinations of atmospheric density dispersions, aerodynamic mispredictions, and off-nominal atmospheric interface conditions. This study demonstrated 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 algorithm can ensure mission success (as measured by the required postaerocapture propulsive maneuvers) in the presence of numerous off-nominal conditions.