Postmortems

""" The Apollo 11 mission succeeded in landing on the moon despite two computer-related

“”"
The Apollo 11 mission succeeded in landing on the moon despite two computer-related problems that affected the Lunar Module during the powered descent. An uncorrected problem in the rendezvous radar interface stole approximately 13% of the computer’s duty cycle, resulting in five program alarms and software restarts. In a less well-known problem, caused by erroneous data, the thrust of the LM’s descent engine fluctuated wildly because the throttle control algorithm was only marginally stable. The explanation of these problems provides an opportunity to describe the operating system of the Apollo flight computers and the lunar landing guidance software.
“”"
http://www.doneyles.com/LM/Tales.html

The article mentions this upset on the next mission: “”“Soggy observers could not see the Saturn V through the rain and clouds. The thousands assembled were alarmed when lightning suddenly flashed from the low clouds into the launch complex area. Inside the spacecraft, everything went dark when lightning tripped the main circuit breakers. Then it suddenly came back on with warning lights flashing. “I think we just got hit by lightning,” Pete Conrad said, with astonishing calm. “We just lost the guidance platform, gang. I don’t know what happened here”.”"" (this text from http://tnmemoirs.com/its-just-technology/) - and again, the computers survived. See Henry Spencer’s take on why: http://yarchive.net/space/apollo/apollo_lightning_hit.html

It’s a long article, but well worth reading through. Eventually it gets to the thrust oscillation: “”“An abort would have been inevitable. With all modesty, it appears to be the case that if the author had coded the “correct” compensation number in the throttle-control routine, Apollo 11 would not have landed.”""