Reciprocating Feed System Development Status
41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit
I. Abstract reciprocating feed system (RFS) is an alternative means of providing high pressure propellant flow T F l o w cost and system mass, with high fail-operational reliability. The RFS functions by storing the liquid propellants in large, low-pressure tanks and then expelling each propellant through two or three small, high-pressure tanks. Each RFS tank is sequentially filled, pressurized, expelled, vented, and refilled so as to provide a constant, or variable, mass flow rate to the
... . This type of system is much lighter than a conventional pressure fed system in part due to the greatly reduced amount of inert tank weight. The delivered payload for an RFS is superior to that of conventional pressure fed systems for conditions of high total impulse and it is competitive with turbopump systems, up to approximately 2000 psi. An advanced version of the RFS uses autogenous pressurization and thrust augmentation to achieve higher performance. In this version, the pressurization gases are combusted in a small engine, thus making the pressurization system, in effect, part of the propulsion system. The RFS appears to be much less expensive than a turbopump system, due to reduced research and development cost and hardware cost, since it is basically composed of small h g h pressure tanks, a pressurization system, and control valves. A major benefit is the high reliability fail-operational mode; in the event of a failure in one of the three tank-systems, it can operate on the two remaining tanks. Other benefits include variable pressure and flow rates, ease of engine restart in micro-gravity, and enhanced propellant acquisition and control under adverse acceleration conditions. We present a system mass analysis tool that accepts user inputs for various design and mission parameters and calculates such output values payload and vehicle weights for the conventional pressure fed system, the RFS, the Autogenous Pressurization Thrust Augmentation (APTA) RFS, and turbopump systems. Using this tool, a preliminary design of a representative crew exploration vehicle (CEV) has been considered. The design parameters selected for a representative system were modeled after the orbital maneuvering system (OMS) on the Shuttle Orbiter, with an increase of roughly a factor of ten in the delta-V capability and a greater thrust (30,000 lbs, vs. 12,000 lbs). Both storable and cryogenic propellants were considered. Results show that a RFS is a low mass alternative to conventional pressure fed systems, with a substantial increase in payload capability and that it is weight-competitive with turbopump systems at low engine pressure (a few hundred psi); at high engine pressures, the APTA RFS appears to offer the highest payload. We also present the status of the RFS test bed fabrication, assembly, and checkout. This test bed is designed to provide flow rates appropriate for engines in the roughly 10,000 to 30,000 lb thrust range. Technical Discussion The basic concept for a RFS is covered in patent number 6,314,978 B1 titled Reciprocating Feed System for Fluids' and in an early AIAA Joint Propulsion Conference paper2. T h s patent was originally assigned to McDonnell Douglas, but was donated to the University of Alabama in Huntsville in 2005. Other UAH patents related to the RFS are pending. Other work related to this topic is addressed by Knight3 , by Flowmetrics4, and in patent number 3,213,804, titled Fluid Pressurizing System'. The RFS contains propellant in both of the main, low pressure, storage tanks and in two or three small, high pressure tanks. The small tanks would be filled initially before engine fring and would also fill after engine shutdown for multiple restart missions. The small tanks would alternately expel fluid into the engine, vent, refill with fluid from the main tank, and then be pressurized. This controlled, alternating cycle provides a uniform, pressurized flow of fuel and oxidizer to the engine. The use of small, lightweight tanks allows the RFS to operate at engine pressure ranges above those normally associated with pressure fed systems.