surface 240 in fig2 to the left for example causes the demand line 406 in fig4 to translate to the right and causing the operating point 410 to move up the supply line 408 in fig4 to increased values of mass flow and pressure conversely movement of the control face 240 to the right in fig4 reduces mass flow and pressure causing the operating point 410 to move down the supply line fig3 of the drawings shows three types of dynamic response or three degrees of dynamic stability which can be experienced from the gas generator of fig2 as a result of instantaneous ignition of the burn surface with the throttle member 220 initially fully closed the oscillatory response 300 shown in fig3 a can be expected when the fig2 apparatus is provided with a spring 232 having a constant preload value and a force exertion which is independent of throttling member position i e a constant force of preload magnitude and a total absence of damping in the member 236 the scales at 306 and 308 in fig3 indicate effective area at 212 in fig2 and elapsed time respectively similar variations of other parameters in the fig2 apparatus such as pressure in the burn chamber or plenum 216 or mass flow at 224 can be used as indications of fig2 gas generator response to stimuli the response 300 in fig3 a represents an undamped oscillatory condition in which throttle position is limited only by physical constraints of the fig2 system such as the travel limits of the throttle member 220 a damped sinusoid response for the fig2 system is indicated at 302 in fig3 b a response of this nature is to be expected with the addition.