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I'd always heard the story about how Apollo 12 was struck by lightning and wondered why they let it head up in a storm. They always check the weather before a launch, and if there is any chance of even a little rain they delay the flight. What was the reason for Apollo 12's exception?

klipty
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From NASA's own website:

With a half hour to go, Merritt Island was experiencing peak winds of 14 knots, light rain showers, broken clouds at 240 meters, and overcast skies at 3,000 meters. But the ceiling exceeded the minimum requirement of 150 meters, and the ground winds were within limits. The Apollo design permitted launch during rain. The possibility of lightning concerned Launch Operations Director Kapryan, however, and he considered a hold.

(...) A weather report from the Eastern Test Range helped Kapryan make up his mind. An Air Force plane reported only mild turbulence and no indication of lightning within 32 kilometers of LC-39. Moonport, Ch22-2

If you want more information on why they continued to launch during the special weather conditions, see these links:

As response to Uwe's anwser:

After the launch some newspapers suggested that President Nixon's presence influenced Kapryan's decision. The launch director denied it. Moonport, Ch22-2

Community
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Thomas Wagenaar
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Apollo 12 actually was not struck by lightning, despite the common misconception. It did fly through rain, and was the only manned spacecraft to fly through rain. In that flight, there was a massive static electricity buildup that lead to the two electrical events. Source

There was a rule, 1-404, that states:

“The vehicle will not be launched when its flight path will carry it through a a cumulonimbus (thunderstorm) cloud formation.”

That in fact was not violated, as it was not actually struck by lightning. The controllers realized they were close to violating that rule, but opted to go ahead and fly the mission. Still, they learned, and as mentioned earlier, this was the last time they attempted to launch in rain, let alone a potential thunderstorm.

PearsonArtPhoto
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  • But still, the rule was waived. Why would they let it go ahead? – klipty Dec 08 '16 at 20:11
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    In Russia, launch in rain, in snow, in blizzard. Unlike wimpy amerikans. (how do you type to sound like a stereo typical Russian accent?) – geoffc Dec 08 '16 at 20:34
  • @geoffc throw in some random cyrillic – Antzi Dec 09 '16 at 07:48
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    @klipty The answer specifically says that the rule was NOT violated. – Antzi Dec 09 '16 at 07:49
  • @Antzi The source says that 1-404 was waived prior to launch, although it ended up not being violated anyways, – klipty Dec 09 '16 at 16:04
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    The source says that it was struck by lightning, but that it was "self-induced", rather than being caused by flying through a thunderstorm. – pericynthion Dec 11 '16 at 23:18
  • This page explicitly says it was not a static buildup and discharge. https://history.nasa.gov/afj/ap12fj/a12-lightningstrike.html#:~:text=Two%20leading%20theories%20emerged%20for%20the%20cause%20of%20the%20lightning%20event Do you have a reason to trust this random PDF over the NASA page? – Tim Dec 03 '23 at 17:02
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May be they did not delay the flight this time because President Richard Nixon attended the launch, see https://en.wikipedia.org/wiki/Apollo_12 and the discussion here http://www.collectspace.com/ubb/Forum29/HTML/001509.html

Uwe
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    Interesting theory, but your second link debunks it. 1st entry: "How much of a factor was Pres. Nixon's attendance …", second entry: "None. I have spoken to Paul Donnelly a couple of times about this. Paul was the Launch Operations Manager at KSC during the Apollo launches." – DarkDust Dec 08 '16 at 11:21