EFFECT OF THE DISTANT POSITION OF A PROPELLANT VALVE ON THE STARTUP DELAY OF A “GREEN”-PROPELLANT THRUSTER

Abstract

In recent years, the leading space countries have paid much attention to a search for and the application of new toxically safe propellants for spacecraft thrusters. A water solution of an ion substance, a fuel, and a stabilizer is used as a “green” propellant. Its feature is a significant increase in the temperature in the thruster reaction chamber in comparison with traditional propellants. Electrically driven propellant valves, which control fuel feed to the reaction chamber in response to thruster startup and shutdown signals, are connected to the reaction chamber via an additional propellant pipeline to provide thermal conditions required for the valve operation. This design solution is responsible for an additional delay between a command signal and a thruster startup, thus complicating the operation of the spacecraft control system. The propellant feed time must be calculated with account for a low pressure in the pipeline, which is characteristic of orbital conditions.

The goal of his work is to calculate the startup delay of a “green”-propellant thruster caused by the propellant valve being at a distance from the propellant nozzles in the reaction chamber under conditions of a vacuumized pipeline.

The paper considers thermophysical processes during the filling of a vacuumized pipeline between the valve outlet and the propellant nozzle and presents a mathematical model that accounts for propellant ebullition and propellant vapor extrusion through the propellant nozzle until the liquid propellant boundary reaches the reaction chamber inlet. The paper presents the liquid propellant flow rate, the vapor pressure, the temperature, and the relative volumes of the liquid and the vapor calculated as a function of time at different values of the propellant tank pressure and the pipeline-to-nozzle diameter ratio for a thruster of nominal thrust 1 N.

It is shown that the effect of the propellant tank pressure and the design parameters of the system of “green” propellant feed to the thruster reaction chamber manifests itself as the thruster startup delay varying in the range from some thousandths to some hundredths of a second, which is comparable with the thruster startup time in the pulsed operation.

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