Servo-stabilization of low-frequency oscillations in liquid propellant rocket motors.

Abstract

Two points of view may be taken with regard to the undesirable pressure oscillations in rocket motors which arise from instability of combustion, acoustic resonance, coupled oscillations of chamber pressure and propellant flow rate, as well as from more obscure sources. One is to eliminate the underlying cause of instability through change in mechanical design or modification of propellant properties; this is possible when the mechanism of instability is understood and its removal is not detrimental to rocket performance. The alternative is, as was demonstrated by H. S. Tsien [1], to modify the system dynamics by utilizing a feedback servo control which, for example, senses pressure fluctuations in the combustion chamber and modifies the propellant feeding rate at the proper frequency and phase to damp the fluctuation. Servo-stabilization provides the distinct advantage that stability need not be a major concern during rocket design, relying upon the feedback system to insure stable operation. Furthermore these concepts suggest the possibility of eliminating empirically an undesirable oscillation even when its basic cause is not known.

Additional details