Mathematical model of “green”-propellant jet thrusters and its verification

Spacecraft’s liquid-propellant jet thrusters serve as spacecraft control system actuators. Their main propellant is hydrazine, which is very toxic and difficult to use. Because of this, in recent years the world’s leading countries have paid much attention to a search for and the use of new untoxic “green” propellants, one of which is a water solution of three components: an ion substance, a fuel, and a stabilizer. A catalyst is installed at the thruster reaction chamber inlet for decomposing the ion substance to give an oxidizer, in whose presence the fuel burns to give high-temperature gaseous products, whose outflow through a supersonic nozzle produces a thrust. The development of thrusters of this type calls for a detailed study of thermochemical and gas-dynamic transformations in the thruster reaction chambers and hydraulic processes in the feed systems. Some of the reported developments of 0.1 N to 220 N “green” propellant thrusters were successfully tested in flight conditions. Ukrainian developers of jet thrusters pay much attention to the use of LMP-103S “green” monopropellant for spacecraft of various purposes. Under development is a propulsion system with several tens of thrusters that differ in thrust scale and operating conditions and are fed from a common propellant tank. Its designing calls for the mathematical simulation of its operation. The goal of this work is to adapt a comprehensive mathematical model of a system of liquid-propellant jet thrusters to LMP-103S monopropellant and verify it using data of single-thruster firing tests in ground and orbital conditions. The paper presents the basics of the adapted mathematical model, which describes an unsteady propellant flow in the pipelines from the tank to the thrusters, thermogas-dynamic processes in the reaction chambers, and the operation of electrically driven propellant valves for each of the thrusters. The model was verified for 1 N, 5 N, and 22 N trusters for different inlet propellant pressures characteristic of flight conditions. The calculated results showed that for a system of thrusters differing in thrust scale, their hydraulic coupling via the propellant feed system may result in their significant interplay, especially for thrusters differing in operating conditions.