The use of high thrust engines on the LEASAT (a communications satellite leased by the Navy) Liquid Apogee Motor (LAM) subsystem, with their associated high flow rates, stimulated a discussion of the possibility of vortexing phenomena within the LAM propellant tanks. Previous liquid propulsion systems were not vulnerable to this phenomena due to either low flow rates or the use of a bladder which eliminated the free surface required for vortex formation. A literature search showed that although a certain amount of qualitative testing has been done, there is no analytical treatment which can be applied with confidence. Therefore, as with previous approaches to the problem, full scale and model testing were done, using the appropriate scaling equations derived from dimensional analyses. The tests were divided into two categories: extensive testing at 1 £, which indicated vortex formation, and limited centrifuge testing which showed no tendency to form vortices in this design.
Nomenclatureg = acceleration, ft/s/s L = length, in. r = radial distance, in. V = velocity, ft/s w = angular velocity, rpm Z = vortex axis of symmetry /i = dynamic viscosity, Ib/ft-s v = kinematic viscosity =/A/p, ft 2 /s p = liquid density, lb/ft 3 Subscripts m = model p = prototype R = ratio of model property to prototype property; e.g.,
Nomenclature a = axial acceleration / = propellant feed line length P = pressure R, r = distance from spacecraft centerline to propellant tank centerline and propellant tank radius, respectively / = time K/ ? vi' = weight of propellant in tank and propellant flow rate, respectively 7 = propellant density A --• indicates difference between parameters 6 =--= direction of resultant force vector or thrust misalignment angle p, = propellant viscosity co = spacecraft angular velocity Dimensionless ratios A* = raj 2 /a y* = 72/71 h* = AP/7Â /* -(/2 -/l)//l ft* = 1^2/^1 R* = R/r A/^* = Afl/r = AH//(f77T 3 7 2 ) = kW = /2//1 component one component two (opposite one) maximum residual total amount Theme M ANUFACTURING tolerances on propulsion systemcomponents and variations in operational environment result in differing amounts of propellant in each tank of a manifolded multiple tank system. This propellant difference causes a mass unbalance which cannot be completely compensated for prior to launch and has been neglected on the majority of spacecraft; however, precision pointing accuracy on communication satellites requires that they be very accurately balanced. 1 " 3 This paper surveys the various causes of propellant unbalance between tanks and presents corresponding estimates.
This paper describes the bipropellant propulsion subsystem for the LEASAT spacecraft. LEASAT is a Shuttle-launched spacecraft which will provide satellite communications services to the United States Navy. Propulsion is provided by three separate subsystems: a solid perigee motor, a bipropellant subsystem, and a monopropellant reaction control subsystem. The solid perigee motor provides impulse to raise the apogee from the Shuttle parking orbit. The bipropellant subsystem, which utilizes monomethyl hydrazine and nitrogen tetroxide, is designed to provide the impulse required for apogee augmentation and injection into synchronous orbit at apogee. The monopropellant hydrazine reaction control subsystem provides the impulse required for spacecraft spinup, apogee augmentation, attitude and spin speed control, and other required on-orbit maneuvers. The subsystem presented herein is scheduled to be flown in 1982, and represents one of the first configurations designed for Shuttle-optimized spacecraft.
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