Vapor jet control of space vehicles

Abstract

This paper describes a reaction jet attitude control technique which affords significant advantages in terms of accuracy, reliability, fuel economy and operational flexibility. These advantages are realized by the use, in combination, of low-thrust vapor jets and time-dependent on-off switching circuits. An accuracy potential comparable to inertia wheel control is thus provided, while the proverbial wheel problems of speed saturation, bearing life, threshold nonlinearities, gyroscopic coupling and vibration excitation are avoided. Very-low thrust magnitudes are attained by simply opening a small orifice to allow fuel to vaporize into the surrounding vacuum. Fuel storage, pressurization, circulation and mixing requirements are thus minimized. By augmenting conventional on-off valve switching circuitry with electronic networks that generate thrust pulses of small but constant time duration, vehicle angular rate can be controlled to a very-low threshold. This minimizes fuel consumption and valve cycling frequency. The capabilities and limitations of this design approach were substantiated by an analog computer program incorporating breadboard switching circuits, and by vacuum chamber testing of critical components. These technique and component developments are applicable to such space missions as astronomical observation, earth reconnaissance and stellar navigation. Design guides are presented for synthesizing a reaction jet system to meet any particular set of performance specifications.