At 73 hours, 46 minutes into the mission, the air-to-ground transcript describes the event: Lovell: OK.
This meant they could only measure the rate of change of orientation rather than measure the absolute orientation. Nearly every NASA mission at this point had a major quirk or two to deal with.
Approximately 8 lbs of plutonium was used for each mission and it was it was transported to the Moon in a thermally insulated cask attached to the side of the Lunar Module.
For thermal control, the crew were simply instructed every so often to manually move the stack around to different attitudes. Everything seemed normal as Apollo 13 made its way through space following launch on April 11, However, the LM closeout was underway, and there was no chance to use the thrusters to change attitude.
A really long tape measure will give you an absolute answer with far more confidence, and so the IMU was the preferred instrument. Previous articles in this series:. He was doing a speaking tour, usually to business audiences, about the kinds of things I mentioned above.