Editing Service module (section)

==Design==
Depending upon the spacecraft architecture and system design, a typical service module usually contain the following:<ref name="csm07" /><ref name=":0" />
* [[Fuel cell]]s, [[solar cell|solar panels]], or [[battery (electricity)|batteries]] to provide electrical power to the spacecraft (batteries are also used in the crew capsule)
* [[Liquid hydrogen]] (LH<sub>2</sub>) and [[liquid oxygen]] (LOX) for fuel cell operation and water production, with LOX also being used to provide breathing oxygen for the crew.
* Pressurized [[helium]] or [[nitrogen]] to force consumables and fuel from source tanks to their destinations.
* Guidance computer systems and related sensors
* Fuel and oxidizer for [[reaction control system|reaction control]] and [[Spacecraft propulsion|propulsion]] systems.
* Thermal control systems for proper heating and cooling of above systems.

While this would be used for a "baseline" service module, a service module may also be modified for additional functions. An example would be the equipment module on [[Gemini 9]], when it was modified to carry the [[U.S. Air Force]]-developed [[Manned Maneuvering Unit|astronaut maneuvering unit]] that would have been tested by astronaut [[Eugene Cernan]], but was cancelled when his spacesuit overheated, causing his visor to fog up. But the best example would be the final three Apollo missions, in which the J-series service modules included scientific instrument module (SIM) bays that took pictures and other readouts in lunar orbit. In addition to the film cameras, similar to those used on the [[Lunar Orbiter]] spacecraft and requiring the Command Module Pilot to perform a deep-space EVA during the return trip, two of the SIM bays, on [[Apollo 15|Apollos 15]] and [[Apollo 16|16]], also launched a lunar "subsatellite" before the astronauts performed the Trans-Earth Injection burn with the onboard service propulsion system.{{citation needed|date=March 2013}}

A unique inhabitable variation of the service module concept is the [[Functional Cargo Block]] developed for the Soviet [[TKS (spacecraft)|TKS Transport Supply Spacecraft]]. In addition to full functionality of a service module, it featured a sizeable pressurized cargo bay, and a docking port – as opposed to its conventional location on the front of the re-entry capsule, which in case of the TKS instead possessed its own downscaled service module with de-orbiting thrusters – allowing the FGB to remain docked as an extension of the space station.{{cn|date=February 2021}}