Control algorithms for aerobraking in the Martian atmosphere

Details Control algorithms for aerobraking in the Martian atmosphere Control algorithms for aerobraking in the Martian atmosphere

Feb 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........77s&link_type=abstract

Ph.D. Thesis Texas A&M Univ., College Station.

Mathematics

Aerobraking, Algorithms, Atmospheric Entry, Controllers, Mars Atmosphere, Trajectory Control, Atmospheric Density, Atmospheric Pressure, Computerized Simulation, Degrees Of Freedom, Gliding, Liapunov Functions, Polynomials, Robustness (Mathematics), Square Waves, Statistical Analysis

Scientific paper

The Analytic Predictor Corrector (APC) and Energy Controller (EC) atmospheric guidance concepts have been adapted to control an interplanetary vehicle aerobraking in the Martian atmosphere. Changes are made to the APC to improve its robustness to density variations. These modifications include adaptation of a new exit phase algorithm, an adaptive transition velocity to initiate the exit phase, refinement of the reference dynamic pressure calculation and two improved density estimation techniques. The modified controller with the hybrid density estimation technique is called the Mars Hybrid Predictor Corrector (MHPC), while the modified controller with a polynomial density estimator is called the Mars Predictor Corrector (MPC). A Lyapunov Steepest Descent Controller (LSDC) is adapted to control the vehicle. The LSDC lacked robustness, so a Lyapunov tracking exit phase algorithm is developed to guide the vehicle along a reference trajectory. The equilibrium glide entry phase is used for the first part of the trajectory. This algorithm, when using the hybrid density estimation technique to define the reference path, is called the Lyapunov Hybrid Tracking Controller (LHTC). With the polynomial density estimator used to define the reference trajectory, the algorithm is called the Lyapunov Tracking Controller (LTC). These four new controllers are tested using a six degree of freedom computer simulation to evaluate their robustness. MARS-GRAM is used to develop realistic atmospheres for the study. The atmospheres are then perturbed using square wave density pulses. The MHPC, MPC, LHTC and LRC show dramatic improvements in robustness over the APC and EC. The MHPC, MPC, LHTC and LTC all complete the initial phase of testing (using square wave density pulses) with no failures. The second phase tests the MHPC, MPC, LHTC and LTC against atmospheres where the inbound and outbound density functions are different. Square wave density pulses are again used, but only for the outbound leg of the trajectory. All four controllers are able to compensate for the outbound leg density pulses with no hard failures, but the algorithms are sensitive to large amplitude density pulses.

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