Design and Evaluation of an Attitude Control System for a Spacecraft Landing Demonstrator

Kurzfassung

As a replacement for toxic hydrazine-based spacecraft propulsion the German Aerospace Center is developing the green propellant combination HyNOx and accompanying thrusters. In order to demonstrate this technology and test novel control strategies a lander demonstrator called "The LÄNDer" is being built. This work presents a model predictive attitude controller that can control the current lander demonstrator hardware, and is capable of being adapted for usage in the planned free-flight demonstrator. The specifics of the attitude control actuators used in the lander demonstrator necessitate its treatment as a set-valued input system. In addition, external forces encountered during atmospheric descent are assumed to be nonlinear and time-varying. It approaches the choice of set-valued inputs as a problem of combinatorial optimization, employing modified path planning algorithms in combination with a nonlinear system model to determine the control action. The impact of several controller parameters is evaluated with Monte Carlo experiments, which were also used for examinations regarding robustness and stability. After evaluation in a simulation environment, the controller is then deployed to the embedded avionics of the lander demonstrator hardware.