Happiness is having plenty of hydrogen

See list attachedMarch 14, 196969-PA-T-44APA/Chief, Apollo Data Priority CoordinationHappiness is having plenty of hydrogen

As I understand it, there has been a desire or requirement to have the capability of surviving a cryo-tank failure at any time in the lunar mission. After C', it was decided to keep the IMU powered up through- out all lunar missions even though it might be at the cost of having the backup cryos. However, according to a recent analysis by MPAD's Guidance and Performance Branch (R. C. Wadle, W. Scott, and D. A. Nelson), these two characteristics are not incompatible. Since this is quite different from what I have heard in the past, I thought you might find it interesting, too.

According to Wadle, Scott, and Nelson, it is possible to operate with the platform powered up and even if one tank fails as late as TEI, there is still enough hydrogen left in the other tank to provide a four day return- to-earth in a powered-down state. (Hydrogen is the most critical consum- able.) The powered-down state still provides for communications; essentially it consists of just taking the guidance system and one fuel cell off-the line and turning off non-essential equipment.