MEASURED PERFORMANCE OF WATER VAPOR JETS FOR SPACE VEHICLE ATTITUDE CONTROL SYSTEMS

SUMMARY Measurements were made to evaluate the performance of water-vapor jets in the thrust range from 5 to 200 dynes. It was found necessary reduce ambient pressure to less than 1 micron to obtain results applicable to a space environment. Under these conditions, the steady-state specific impulse was 58 to 65 percent of the value expected for isentropic flow regardless of nozzle size. The specific impulse measured for a train of pulses was always found to be less than that for steady thrust. For pulses lasting 1/2 to 5 seconds, the measured specific impulse was 10 to 25 percent less than the steady-state value. INTRODUCTION Disturbances encounted by unmanned spacecraft causing errors in attitude and in orbital position are inherently small. Analyses of jet systems for con- trolling attitude have shown that the mass of propellant required is minimized when the impulse delivered by the control system is sufficient to just overcome the disturbances. Control of orbital position,