MATHEMATICAL MODELING OF THROTTLEABLE PROPULSION SYSTEM FOR LUNAR LANDER
Propulsion systems involve complex interconnected processes of flow, combustion and thrust production with components exhibiting dynamic characteristics. The functioning of one component in the engine circuit may depend on a parameter that in turn depends on the characteristics of all other remaining sub-systems. Typical lunar missions involve deployment of an orbiter and a soft landing lander module that will release a rover for lunar exploration. The propulsion system configuration considered for this work consists of four throttleable 800N bipropellant pressure fed engines. All engines draw propellants from the same fuel and oxidizer tanks. The tank pressures are regulated using pressure regulator and helium gas bottle is used for the source pressure. The mission demands sudden shut-off and throttling of engines. Engine shut off create pressure peaks in the fluid components and affect its performance. Variable area valves in the fluid circuit are used to control the thrust output of the engines. If thrust demand is changed, there will be changed mass flow rates through the respective engine feed lines which in turn cause the propellant tank pressure to vary. Hence the system is highly coupled and a detailed model is called for precise prediction of the system behavior. The model was developed in Simulink and was subsequently used for input generation and predictions for ground tests.