Service Module

The Apollo Launch stack comprised of three modules and a booster. The Command Module (CM) served as the crew's quarters and flight control section. The Service Module (SM) was used for the propulsion and spacecraft support systems. The command and service modules together were called the Command-and-Service Module, or CSM. The Lunar Module, or LM, pronounced "lem," transported two crew members to the lunar surface and back to the waiting CSM.

The Service Module had what was known as an SPS (Service Propulsion Subsystem). This provides the thrust for all major velocity changes throughout a mission. These include the retro braking manoeuvre for insertion into an orbit around the moon, the thrust for injection into the transearth trajectory major course corrections, and the power to return the CM to earth's atmosphere during an abort after the launch escape subsystem has been jettisoned. The subsystem includes a single large rocket engine, its pressurization and propellant subsystems, a bipropellant valve assembly, a thrust mount assembly with a gimbal actuator assembly, and the propellant utilization and gauging subsystem. Displays and sensing devices enable the crew and ground stations to monitor subsystem performance.

It also powered the Command Module during the mission, the CM did have its own power except small batteries for life support during re-entry and to deploy the parachutes. The SM provided the rest of life support needs during the mission.

CSM

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        Service Module

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	              Command Module