Apollo 13 (mission)
Apollo spacecraft concepts
An Apollo spacecraft, configured for lunar missions, had three components:
- Command Module (CM), which could reenter earth atmosphere and held the crew
- Service Module, containing fuel cells for power and oxygen, and other support systems; not accessible to the crew; the explosion that damaged Apollo 13 was part of a fuel cell system in the Service module
- Lunar Excursion Module (LEM), which became accessible to the crew after launch and orbit; the airlock of the CM mated with that of the LEM.
In a normal mission, the Lunar Module, capable of landing on and taking off from the Moon, would undock and dock for the actual exploration mission. After the explosion, the crew used it in a contingency mode called Lunar Lifeboat Mode, in which resources aboard the LEM substituted for those in the SM.