Abstract: An injector assembly 10 for injecting fuel and oxidizer in a combustion chamber 38 of a fluid-fueled rocket engine. Injector assembly 10 comprises a stationary housing 12, a plate member 14 attached to the housing 12, at least one injector subassembly 18 and actuation means 16. Each injector subassembly 18 includes a plug 44 attached to the housing 12 and a movable elongated throttle means 64 connected to the actuation means 16. When the throttle is at least partially open, fuel flows through inlet 20, orifice 110, inner passageway 66, orifice 112 and finally to the combustion chamber 38. Oxidizer flows through inlet 22, orifice 114, outer passageway 68, orifice 116 and finally to the combustion chamber 38. Controlling the flow of propellants at upstream orifices 110,114 controls the propellant pressure at the downstream orifices 112,116 during thrust level changes and corresponding combustion chamber pressure changes of the engine, thereby maintaining a constant stream momentum and combustion efficiency.