Abstract

A positive displacement pistonless rocket fuel pump uses two pumping chambers alternately filled and pressurized in sequence to maintain a steady flow of pressurized propellant to a rocket engine. This pump fills the gap between pressure fed and turbopump rockets by making a lower cost rocket feasible without the weight of a pressure fed design or the high cost and complexity of a turbopump. The pump, combined with a lower pressure tank, saves up to 90% of the tank weight in a comparable pressure fed system. Thrust to weight ratios are calculated for the pump using typical fuel combinations. For a 2219 aluminum LOX/RP-1 pump at 4 MPa the thrust/weight ratio of the pump is ~700. Design and test data for a prototype which pumps water at 3.5 MPa and 1.2 kg/s is presented. The simple construction of the pump allows for low cost, reliable propulsion systems. This pump has been tested with liquid nitrogen and kerosene. It has also been used to pump kerosene with a rocket engine.

Introduction

With the advent of low cost ablative liquid fueled rocket engines and composite tanks, the problem of propellant pressurization becomes the last stumbling block to affordable launchers. Turbopumps are currently used in the majority of launch vehicles, although piston pumps have been designed and flown1 and pneumatic diaphragm pumps have been proposed by Godwin2and Sobey.3 The pump considered herein is much simpler and less expensive than a turbopump. The pump concept is simple: instead of having the whole fuel tank pressurized to 2-7 MPa, the main tank is at pressurized to 100-400 kPa and it is drained into a pump chamber, and then the pump chamber is pressurized to deliver fuel to the engine. An auxiliary chamber supplies fuel while the main pump chamber is being refilled. This type of pump has benign failure modes, can be installed in the fuel tank to minimize vehicle size and uses inexpensive materials and processes in its construction. With the right choice of materials, the pump will be compatible with all common rocket fuels. The pump can be started instantly, with no spool up time required. It can be run until the tank is dry with no concerns about cavitation or overspeeding. The simplicity and low cost of the pump allows for systems with engine out capability or allows for the use of tri-propellant systems. This pump lends itself to mass production techniques for low cost systems with multiple engines and tanks. The pump can be easily scaled up or down with no loss of performance. The pump can be stored for a long time with no degradation.