"Bruce Palmer" wrote in message
et...
Derek Lyons wrote:
rk wrote:

Kevin Willoughby wrote:

Does any of that explain why the S-V guidance computer worked just fine
when the Apollo computer had been knocked sideways by lighting on
Apollo
12?

I don't know, have no data, but I always thought about just that issue.

The explanation I heard was that the Apollo computer being in a
smaller volume and nearer the strike was exposed to higher EMF effects
than the S-V computer.

Were the Saturn V guidance computers in the IU with the stable reference
platform?

Apollo 12 was struck twice by lightning ISTR. Were the actual locations
of the lightning strikes on the vehicle documented?

--
bp
Proud Member of the Human O-Ring Society Since 2003

digs up trusty copy of Murray and Cox ...

The way it's explained there, Apollo 12 created its own lightning ... (pp.
376-7)

" ... What they had done, they realized later, was to launch a 363-foot
lightning rod, with the equivalent of a copper wire in the form of a trail
of ionized gases running all the way to the ground. Even though there was no
lightning in the vicinity before launch, Apollo 12 could create its own. And
that is exactly what it did, discharging the cloud into which it had entered
....

"Actually, Don Arabian's anomalies team later determined that Yankee Clipper
was hit twice by lightning, once 36.5 seconds after launch at an altitude of
6,000 feet, when it discharged the cloud it was flying through, and again 16
seconds later, when it triggered a cloud-to-cloud bolt."

So it sounds like both bolts hit near the top of the stack (possibly the
LES) first. Apparently, the only physical damage that reuslted from that
60,000-plus-ampere jolt flowing through the skin of the stack was to some
external instrumentation for measuring temperatures and R.C.S. reserves. It
was the induced electromagnetic fields that knocked the fuel cells off line
and tumbled the CM's guidance platform.

And, in a footnote ...

"Part of the reason the spacecraft was so affected by the lightning while
the Saturn was not involved the spacecraft's greater exposure-it was
positioned like the tip of a lightning rod-and part of it was luck, as
Arabian emphatically pointed out ... In the case of the I.U., induced
currents reached the guidance system's circuits but the computer software
kept the platform from tumbling."

I'm guessing that, in addition to being better protected, the differences in
construction and the built-in redundancy of the guidance computers in the
I.U. (thanks, rk, for enlightening me on that with your earlier post) were
why that platform didn't tumble ... thank goodness.

Sorry for the overlong post ... now resuming normal lurking mode ...

James (who still has much to learn)