Five Pound Bipropellant Engine

The objective of the contract described herein was to develop and demonstrate the technology required to provide a high performance, lonq lived, fast response five-pound-thrust bipropellant engine capability for attitude control functions typical of future Air Force requirements.Sptcifically, a step function improvement from the characteristics of monopropellant hydrazine thrusters in the same thrust class was desired.The goals of the technical effort were to provide specific Impulse values of 240 and 300 sec in pulsing and steady state modes of operation, respectively, minimum impulse bits of 0.050 lb-sec or less, repeatable within +10%, and valve response times of 0.005 sec with the pulse mode characteristics attained equally well on the first and subsequent pulses of a pulse mode duty cycle.In addition, it was intended that the engine would be capable of virtually unlimited quantities of cold starts, operate with propellant temperatures ranging from 20 to 120 o F, be suitable for pressure regulated or blowdown pressurization systems and have unlimited duty cycle capability operating in a fully insulated (adiabatic wall) or radiation-cooled configuration.System studies conducted early in the program verified the need for broad range capabilities as it was found that various spacecraft designs have entirely unlike requirements.Initial analytic studies indicated that low dribble volume multi element injector designs were essential if the pulsing and steady state performance goals were to be achieved with a single engine.Early full scale thruster firings disclosed that the 300 sec steady state and 240 sec specific impulse goals were achieveable using a 100:1 expansion nozzle.Long duration operation of a fully insulated unit, however, would require increased barrier cooling with an attendant performance reduction to insure maintenance of the chamber wall at an acceptable temperature.The result of this initial work was that three variants of a basic engine design were fabricated for the program's Task III demonstration testing.These engines all utilized suicide coated columbium thrust chambers with multi element transverse platelet injectors which were integral with a torque in Summary (cont.)motor actuated blpropellant valve, and provided a dribble volume of % 0.0003 3 in.for each propellant.Specific engine to engine differences in the injector patterns traded performance with maximum feed pressure blowdown capability, the ability to operate with an adiabatic chamber wall, and heat flow to the spacecraft.All engines were successfully tested for extended simulated mission duly cycles accumulating more than 400,000 starts and 17,000 sec of firing without mishap.The demonstrated values of valve response and minimum impulse surpassed the goals by margins approaching 100%.The repeatability of the 0.05 lb Impulse bits were + 2.4%.In continuous pulsing steady state performance varied with installation and blowdown caoability as follows:IV