Apollo 14 Command Module

After separating from the command module in lunar orbit, the LM Antares had two serious problems. First, the LM computer began getting an ABORT signal from a faulty switch. NASA believed the computer might be getting erroneous readings like this if a tiny ball of solder had shaken loose and was floating between the switch and the contact, closing the circuit. The immediate solution – tapping on the panel next to the switch – did work briefly, but the circuit soon closed again. If the problem recurred after the descent engine fired, the computer would think the signal was real and would initiate an auto-abort, causing the ascent stage to separate from the descent stage and climb back into orbit. NASA and the software teams at the Massachusetts Institute of Technology scrambled to find a solution. The software was hard-wired, preventing it from being updated directly. The fix involved indicating that abort mode was already active, so that if the signal were to arise again, it would be ignored rather than initiating what would have appeared to the software to be a second abort. The software modifications were transmitted to the crew via voice communication, and Mitchell manually entered the changes (amounting to over 80 keystrokes on the LM computer pad) just in time.