Preparing the CSM

Most of the preparation of the CSM and LM was completed while the mobile support structure was still around the space vehicle. All the food and equipment in the two craft had been packed into their designated storage spaces, and their propulsion tanks filled with storable propellant long before loading of the Saturn V began, ensuring that, on the day of launch, only a few final tasks remained to be completed by hand. Throughout the countdown, and for much of the journey to the Moon, the LM was without power and inert, saving its precious batteries for its foray to the lunar surface. The CSM, on the other hand, was a buzzing, vibrant machine whose health was monitored closely by flight controllers and contractors throughout the countdown in case a problem occurred.

While it sat on the launch pad, it was powered by electricity supplied from the ground. For flight, power came from fuel cells that made

The Apollo 8 CSM as the MSS was withdrawn.

electricity by reacting hydrogen and oxygen from tanks in the service module. Two days before launch, these tanks were filled with reactants and their contents checked for contamination before being introduced to the fuel cells. Rechargeable chemical batteries augmented the spacecraft's power requirements in space, and these were fully charged as part of the launch preparations.

One member of the backup crew, usually the backup command module pilot, entered the command module prior to the crew's arrival and ran through an extensive checklist to ensure that every switch, knob and indicator was in the appropriate position for launch. There were hundreds of these, each taking a line of the checklist. In the later Apollo flights, there were over 450 lines to be checked before the prime crew arrived. With that done, the backup crewman usually waited for the crew to arrive at the white room before he retired to the launch control centre to continue working with them by voice up to the point of launch.

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