Command Module / Service Module
The Command Module / Service Module makes up the main crew areas used on the Apollo Missions. The Lunar Module also became part of the crew areas after leaving Earth Orbit.
Service Module / Command Module on display at Kennedy Space Center
The Command Module housed the crew, spacecraft operation systems and re-entry equipment. The Service Module carried most of the consumable of the mission (oxygen, water, helium, fuel cells, and fuel, and the main propulsion system. The total length of the two modules was about 36 feet long and almost 13 feet in diameter.
Some other interesting bits of info: the Command Module contains over 15 miles of wiring; the 3 main re-entry parachutes are made of nearly an acre of cloth and more than a mile of suspension lines, yet when packed to fit inside the Command Module, all 3 could fit inside a small suitcase. Although Apollo's Command Module must have felt roomy compared to the Mercury and Gemini capsules, it still allowed only 73 cubic feet of space per astronaut.
Service Module Engine
After launch, the Lunar Module would be extracted from its storage housing and dock with the Command Module, remaining there until reaching the lunar orbit. Once in lunar orbit, the Lunar Module would undock from the Command module, and descend to the lunar surface.
Scientific Instrument Module (SIM)
On the outside of the Service Module is the open bay designated as the Scientific Instrument Module. This module included a number of scientific experiments as well as photographic equipment used in mapping the lunar surface.
The Lunar Mapping Camera system created images that had a high degree of geometric precision including recording of the spacecraft's orientation and altitude at the time the image was made. From these images and information detailed topographic and geologic maps of the lunar surface were created.
Once the Lunar Module returned from the service, during an Extra Vehicular Activity (EVA) the SIM bay film would be retrieved during the return flight to Earth before jettisoning the Service Module in preparation for re-entry.
NASA PHOTO: Apollo 17's Command Module Pilot Ron Evans, is shown during an EVA retrieving the film canister from the SIM Bay.
Here instruments that were carried in the SIM Bay on Apollos 15 and 16 included a panoramic camera, as well as X-ray, Alpha-particle, gamma-ray, and mass spectrometers to investigate the properties of the lunar surface. Apollo 17 carried a slightly different set of instruments, including the mapping and panoramic camera systems, a radar system, an infrared scanning radiometer, and an ultraviolet scanning radiometer.