cew@ISI-HOBGOBLIN.ARPA (Craig E. Ward) (10/09/85)
I am looking for information on why the landing computer failed on the Apollo 11 LEM. All that I have come up with so far is a vague reference in Collins' book Carrying the Fire to the error codes 1202 and 1201 which translate to some sort of overflow condition. Please send replies and references directly to me. Thanks, Craig
CLJones@MIT-MULTICS.ARPA (Chris Jones) (10/16/85)
I recall that these were data overflow errors, and were caused by a radar of some sort mistakenly being left on. Apparently the program did OK, discarding the data it couldn't process quickly enough. I don't recall if the crew took any action other than "ignore it--press on". It turned out that Eagle landed around 4 miles farther downrange than intended--I also don't know if this error had anything to do with that. In the end, Armstrong took manual control when he saw the automatic pilot was heading Eagle for a field strewn with large rocks. There were anxious moments on the ground when they saw Eagle's forward speed increase to around 60 mph to cross the boulder field. On the tapes you can hear the ground reminding Eagle that they have only 60, then 30 seconds of fuel left. When Eagle finally touched down, there was under 20 seconds of fuel left before they would have had to punch out and use the ascent engine to get out of there.
karn@petrus.UUCP (Phil R. Karn) (10/17/85)
> It > turned out that Eagle landed around 4 miles farther downrange than > intended--I also don't know if this error had anything to do with that. This error was due to an incomplete model of the moons very complex gravitational field. The moon has a very irregular shape, and unless it is modeled exactly in the programs that simulate an orbit, errors will accumulate. When Eagle was given its final "state vector" (position and velocity) before powered descent initiation, it was actually 6800 meters further downrange and 1400 meters further south. Therefore, the entire descent was shifted downrange and Eagle landed 7km downrange from the original target spot. The desire to demonstrate a pinpoint landing capability was the reason the next flight, Apollo 12, was landed next to Surveyor III. Phil