THE APOLLO SPACECRAFTDeveloped from Mercury and Gemini technology, the Apollo spacecraft itself consisted of the combined
Command and Service Module (CSM). It was 10.4 m (34 ft) long and 3 m (10 ft) in diameter at the blunt end. A major advance over earlier spacecraft was the inertial guidance system developed by the Massachusetts Institute of Technology.The CSM was actually two modules. The crew rode in the Command Module (CM), which contained three couches and was pressurized with oxygen at 0.35 kg/cm6 (5 lb/in6). For
reentry, the CM separated from the Service Module; a heat shield protected it during reentry. During the first stage of the descent, the CM was stabilized by its own reaction control system. During the last stage it employed a drogue and three main parachutes.Behind the CM was the Service Module (SM), which housed the main
engine, of 9,670-kg (21,500-lb) thrust, the reaction control system, fuel cell batteries, oxygen and hydrogen tanks, and environmental control system. The main engine was used for course corrections and major changes in orbit, including the injection of the vehicle into lunar orbit and its escape from lunar orbit for return to Earth.