Manufactured by Aerojet General Corporation, the Apollo Service Propulsion System (SPS) engine provided the thrust necessary to launch the Apollo Command, Service, and Lunar Module assembly into and out of lunar orbit. With only one combustion chamber and expansion nozzle in space, engineers designed a simple SPS 20,500-pound thrust engine to perform flawlessly each time. Instead of mechanical pumps with moving parts, helium forced fuel and oxidizer into the combustion chamber. With no throttle, the engine either burned wide open or was off. To simplify the ignition system, the SPS engine’s fuel and oxidizer ignited on contact with each other.

The Apollo 7 mission tested the SPS engine’s reliability and fired the engine eight times during the mission. It performed flawlessly on all tests, as it did throughout the entire Apollo program.

The Apollo Service Propulsion System (SPS) engine and exhaust nozzle are displayed in the Museum’s Space Age Gallery near the Apollo 7 Command Module. The scorch marks on the upper inside of the exhaust nozzle indicate the test firing of this engine. It is on loan from the Smithsonian National Air & Space Museum.