Experimental Assessment of the Reciprocating Feed System

The primary goal of this pr oject was to design, construct, and test a full scale, high pressure simulated propellant feed system test bed that could evaluate the ability of the Reciprocating Feed System (RFS) to provide essentially constant flow rates and pressures to a rocket engin e. The two key issues addressed were the effects of the transition of the drain cycle from tank to tank and the benefits of other hardware such as accumulators to provide a constant pressure flow rate out of the RFS. The test bed provided 500 psi flow at rates of the order of those required for engines in the 20,000 lbf thrust class (e.g., 20 to 40 lbs/sec). A control system was developed in conjunction with the test article and automated system operation was achieved. Pre -test planning and acceptance a ctivities such as a documented procedure and hazard analysis were conducted and the operation of the test article was approved by, and conducted in coordination with, appropriate NASA Marshall Space Flight Center personnel under a Space Act Agreement. Tes ts demonstrated successful control of flow rates and pressures. II. Technical Discussion The basic concept for an RFS is covered in patent number 6,314,978B1 titled Reciprocating Feed System for Fluids 1 and in prior AIAA Joint Propulsion Conference pa pers 2, 3 . This patent was originally assigned to McDonnell Douglas (a wholly owned subsidiary of The Boeing Company), but was donated to the University of Alabama in Huntsville in 2005. Other UAH patents related to the RFS are pending. Other work relate d to this topic is addressed by Flowmetrics 3-6 , and in patent number 3,213,804, titled Fluid Pressurizing System 7 . The RFS contains propellant in both of the main, low pressure, storage tanks and in two or, preferably, three, small, high pressure tanks. The small tanks would be filled initially before engine firing and would also fill after engine shutdown for multiple restart missions; this provides a significant improvement in the conditions needed for successful propellant acquisition in a microgravity environment, in that the static pressure exerted on surface tension screen devices is far less than for the larger main tanks. The small tanks sequentially expel liquid into the engine, vent, refill with liquid from the main tank, and then are re -pressur ized. Our test results show that this cycle provides an essentially uniform pressure and flow rate. The use of small, lightweight tanks allows the RFS to operate at engine pressure ranges well above those normally associated with pressure fed systems and in the range of the majority of pump fed engines. This higher engine pressure results in smaller engines, increased expansion ratios, and higher specific impulses, all of which contribute to an overall increase in system performance, especially in terms o f delivered payload for constant mission parameters, such as delta -V and thrust. III. Introduction The primary goal of experimental work relating to this project was to design, construct, and test an apparatus that could evaluate the ability of the RF S to provide controlled flow rate and pressure. The two key issues addressed were the effects of the transition of the drain cycle from tank to tank and the assessment of ancillary hardware such as accumulators to provide a constant pressure and flow rate out of the RFS. A control system was developed in conjunction with the test article and automated system controllability was achieved. Finally, pre -test activities such as a documented procedure and hazard analysis were conducted and the operation of th e test article was approved by, and conducted in cooperation with, NASA Marshall Space Flight Center personnel under a Space Act Agreement.