Design and evaluation of a 200 N HYNOX thruster control algorithm in a hardware in the loop simulation of a landing demonstrator

Kurzfassung

At the German Aerospace Center’s (DLR) facility in Lampoldshausen research on less expensive alternatives for hydrazine as rocket propellant is conducted. The propellant combination of nitrous oxide (N2O) and ethane (C2H6) is considered as such. Currently, tests on rocket engines using those propellants are conducted to evaluate their performance. Furthermore, a free flight landing demonstrator for research on planetary soft landings is developed at DLR. Using green propellants and advanced control algorithms, a 30 s flight is to be demonstrated. In this publication, the feasibility of a main engine thrust controller for a 200 N thruster using gaseous nitrous oxide and ethane shall be investigated. A control valve is inserted into the ethane and nitrous oxide feeding line on the existing M11.5 test bench. Then, a control algorithm is developed. It uses model-based feed-forward control to enable a quick response time. Furthermore, A internal engine model in conjunction with a proportional-integral controller is implemented to enable precise control behavior. To prove feasibility, a hardware in the loop simulation is conducted, where combustion chamber pressure measurements are fed into a flight simulation with internal flight controller. The flight controller then computes a desired thrust value based on the lander’s flight state inside the simulation and forwards it to the test setup, where the thrust controller follows this value in a thruster hot fire test. Analysis of these simulation tests conclude a feasible control behavior of the control circle regarding a free flight demonstration.