In the VTSPS, the thrust of the nozzles is controlled by changing the nozzle throat area using a pintle actuator.
In this way, the ratio of total nozzle throat area to chamber pressure will remain constant when the nozzle throat area is varied linearly by the pintle actuator movement.
Since the free volume inside the chamber tends to change with propellant combustion, the chamber pressure is controlled by varying the nozzle throat area. The throat area At can be varied via a pintle actuator.
The thrust capacity of the VTSPS depends on the chamber pressure [P.sub.c] and the total nozzle throat area [A.sub.t] such that
Since there are four DCS nozzles, as shown in Figure 2, the most direct approach would be to command the four actuators by controlling each nozzle throat area independently.
For example, if the y-axis actuator moves toward the +y direction, this will simultaneously reduce the +y nozzle throat area and enlarge the -y nozzle throat area, because the movement of the +y ball valve toward the nozzle moves the -y ball valve away from the nozzle.
If the nozzle throat area can be expressed as a linear function with respect to the pintle actuator displacement, the nozzle throat area can be controlled to meet the maximized DCS thrust efficiency, while maintaining pressure.
From the desired DCS nozzle throat area, three valve commands can be achieved.
Since all of the pintles are moved, this means the net nozzle throat area is changed, and there is no net thrust, and only the pressure control will be affected.
To maintain constant flow and backpressure, the exhaust nozzle throat area
must increase 50 to 100 percent over its normal cruise operation size.