LEASAT liquid apogee motor subsystem performance

Abstract

This paper describes the performance of the bipropellant propulsion subsystem for the LEASAT spacecraft. Two LEASAT spacecraft have been successfully Shuttle-launched and are currently providing satellite communications services to the United States Navy. Spacecraft propulsion incorporates three separate subsystems: A solid perigee motor, a bipropellant subsystem, and a monopropellant reaction-control subsystem. The solid perigee motor provides impulse to raise orbital apogee from the Shuttle parking orbit. The bipropellant subsystem, which utilizes monomethylhydrazine and nitrogen tetroxide, provides the impulse required for apogee augmentation and injection into synchronous orbit at apogee. The monopropellant reaction control subystem supplies the impulse required for spacecraft spinup, apogee augmentation, attitude and spin speed control, and other required on-orbit maneuvering impulse throughout the operational life of the spacecraft. The LEASAT spacecraft were launched in August and November of 1984. The flight data obtained support the results of analytical modeling and subsystem level test data as well as performance data supplied by vendors. Nomenclatureacceleration due to spacecraft spin hi = distance between fluid level and equilibrium level H = total fluid head K1-K4 = constants derived from thruster data P c = chamber pressure P in = thruster inlet pressure Q = volumetric flow rate Re = Reynolds number w = propellant flow rate [i = viscosity p = density T =time constant <i> =sun angle Subscripts f = fuel ox t = oxidizer = total