Entry Vehicle Performance Analysis and Atmospheric Guidance Algorithm for Precision Landing on Mars

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Entry Vehicle Performance Analysis and Atmospheric Guidance Algorithm for Precision Landing on Mars

T. A. Dierlam

Future missions to Mars may require pin-point landing precision, possibly on the order of tens of meters. The ability to reach a target while meeting a dynamic pressure constraint to ensure safe parachute deployment is complicated at Mars by low atmospheric density, high atmospheric uncertainty, and the desire to employ only bank angle control. The vehicle aerodynamic performance requirements and guidance necessary for a 0.5 to 1.5 lift-to-drag ratio vehicle to maximize the achievable footprint while meeting the constraints are examined. A parametric study of the various factors related to entry vehicle performance in the mars environment is undertaken to develop general vehicle aerodynamic design requirements. The combination of low lift-to-drag ratio and low atmospheric density at Mars results in a large phugoid motion involving the dynamic pressure which complicates trajectory control. Vehicle ballistic coefficient is demonstrated to be the predominant characteristic affecting final dynamic pressure. A speed brake is shown to be ineffective at reducing the final dynamic pressure. An adaptive precision entry atmospheric guidance scheme is presented. The guidance uses a numeric predictor-corrector algorithm to control downrange, an azimuth controller to govern crossrange, and an analytic control law to reduce the final dynamic pressure. Guidance performance is tested against a variety of dispersions, and the results from selected test causes are presented. Precision entry using bank angle control only demonstrated to be feasible at Mars.