Re: Dyna-Soar question

In article <IE4HLG.2Lp@xxxxxxxxxxxxx>, henry@xxxxxxxxxxxxx says...
> In article <4d66d02a.0503290806.7c51a7ba@xxxxxxxxxxxxxxxxxx>,
> carmine9 <maximusDlll@xxxxxxxxxxxx> wrote:
>
> <snip>
>
> > How close was Apollo 12 to reverting manual control following the
> >lightning strike (I understand the spacecraft and launcher each was
> >independently capable of controlling the ascent, but how much
> >degradation, if any, was there?)
>
> The spacecraft electronics were pretty much completely scrambled, and had
> to be reset and (after reaching orbit) realigned, but the launcher
> computer was unaffected and continued the ascent as if nothing had
> happened.

In fact, Apollo 12 was probably the *only* flight after the "manual"
Saturn V steering option was added that could *not* have reverted to
such a mode had the Instrument Unit of the Saturn gone belly-up. Conrad
had no platform and no balls (8-balls, that is) that would have been
needed to guide the stack.

But the possibilities are interesting, here... As a quick recap of what
actually happened, Apollo 12 was struck *twice* by lightning. The first
strike knocked the fuel cells offline, resulting in the Christmas=tree
display of every single EPS caution/warning light flashing on at once.
The second strike interrupted power to the IMU, causing it to lose its
inertial lock and indeed causing it to tumble aimlessly for a time.
Both strikes caused minor transients in the IU, which were ignored by
the Saturn's flight controls (as the system was designed to do when such
transients occurred).

Now, during Apollo 12's launch, had the first lightning strike caused a
more significant glitch in the Saturn's IU, Conrad *might* have taken
manual control of the stack, even though his EPS was on the fritz. And
26 seconds later, his own platform would have tumbled and he would have
had *zero* attitude reference by which to fly. At which point the only
tihng left to do would have been to punch off and dump a quarter-of-a-
billion-dollar moon mission into the ocean.

Now, I'm aware that there was a "worst case scenario" manual control
option that assumed loss of the CMC and/or the platform as well as loss
of the IU, but that mode was not available until, IIRC, late in the S-II
burn or early in the first S-IVB burn. In that mode, the CDR used the
horizon and certain scribe marks on his window to maintain proper
attitude. Gene Cernan even convinced mission planners to retain the
option on Apollo 17, insisting that, if he had to, he would be able to
maintain attitude by eyeballing the starfield (since, of course, Apollo
17 didn't have the luxury of a lighted horizon during boost phase). The
kicker there is that, in the post-flight debriefing, Cernan admitted
that, even with the cabin lights turned as low as possible, he couldn't
see any stars out the window during boost...

--

"The problem isn't that there are so | Doug Van Dorn
many fools; it's that lightning isn't | dvandorn1@xxxxxxxxxxxxxxxx
distributed right." -Mark Twain
.

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