|astronautix.com||Block I Apollo CM's heat rejection capability inadequate|
Analysis by MSC of the performance of the environmental control system radiators for Block I CM's placed their heat rejection capability at 4,000 Btus per hr, far below the anticipated mission load of 7,220.
Water boiled at the rate of 1.46 kg (3.22 lbs) per hr would be needed to supplement the radiators. This, in turn, would limit the mission to 45 hours duration, at which time all of the spacecraft's water supplies (both that in the water tanks at launch and that collected as a byproduct from the fuel cells) would be exhausted.
As MSC saw it, potential solutions were to redesign the radiators themselves, to increase the size of the tanks to hold another 194 kg (428 lbs) of water, or to reduce the operating power level. References: 16 .