Fuel cell purges

The spacecraft's three fuel cells use the chemical reaction of hydrogen and oxygen, stored in cryogenic tanks, to produce the majority of electrical power for the CSM. The by-products from this chemistry are heat and water. The heat is discarded through eight radiators around the upper circumference of the Service Module. The water can be used for drinking or equipment cooling. Impurities in the reactants build up on the electrolyte and a purge is required at regular intervals to remove them and restore full capability. Purges with oxygen are carried out daily, but once every two days suffices for hydrogen purges. Controls on the right-hand side of the Main Display Console are provided for these functions. (ap15fj)