Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Apollo 6
Date: Tue, 5 Aug 1997 15:32:50 GMT

In article <cbingmanEEFL6n.67r@netcom.com>,
Craig Bingman <cbingman@netcom.com> wrote:
>>...It *was* pretty much a failure -- the reentry test got
>>done, more or less, but the Saturn V had a lot of trouble...
>
>This is the "pogo" effect mission, right?

Pogo effect in the first stage, double engine failure in the second stage,
engine-restart failure in the third stage, and a structural failure in the
LM adapter panels during ascent.  The CSM was just about the only thing
that *didn't* break in some way.

>Why is it that we (humans) tend to say that any mission that didn't go
>exactly as planned is a failure.  I personally think that unmanned
>mission was a great success, because it gave valuable data that kept
>astronauts alive and assured the success of later manned missions.

You can learn a lot from a failure, but it remains a failure.  About the
best thing anyone could say about Apollo 6 was "had it been manned, the
crew would have survived".  This was in early April; in mid-September,
with Apollo 8 launch preparations well underway, NASA was still debating
whether it should be flown as another unmanned test.  That, and not the
question of Earth orbit vs. lunar orbit, was the major mission-planning
decision for Apollo 8, and it was a difficult call.

>We qualified the S-V in a very small number of missions.  Each of them
>was extremely expensive, a small number of hundred million $, I believe.

Nobody was particularly worried about the price tag at the time.  Apollo 8
probably would have flown unmanned if it hadn't been for schedule pressure,
both from the Kennedy deadline and from intelligence indications that the
Russians were almost ready for a manned lunar flyby.

>We learned enough from them to not have a failed mission with humans on the
>end of the launch vehicle due to the Saturn launch vehicle.

Apollo 13 actually came within a hairsbreadth of being a catastrophic
launch failure.  Although you really have to dig to find out about it,
that unexpected engine shutdown in the second stage saved the second stage
from massive structural failure.  The affected engine had the worst case
of pogo oscillation anyone had ever seen, and the second-stage structure
couldn't have taken it much longer; by sheer luck, the engine's average
chamber pressure had deteriorated to the point where the Saturn's computer
became suspicious and shut it down.  You'd have heard a lot more about
this if (a) later events on Apollo 13 hadn't overshadowed it, and (b) a
fix for the oscillations hadn't been in the pipeline already.

>High five to them, pogo effect and all.  Manned missions got added
>baffles to prevent propellant sloshing.

Uh, sorry, no, propellant sloshing wasn't involved.  Pogo fixes did get
made, ditto changes to the J-2 plumbing, ditto modifications to the LM
adapter structure.  And things more or less worked until Apollo 13, and
thereafter.  But the Saturn V was never really completely debugged; for
example, the second stage was never completely pogo-free, and there was
some pogo in the *third* stage of Apollo 10 that was never explained.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu

Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Apollo brush with potential disaster ?(was merits of STS)
Date: Sun, 18 Jan 1998 03:53:06 GMT

In article <01bd2386$dd7a1fc0$LocalHost@default>,
Gordon Davie <G.Davie@btinternet.com> wrote:
>> >...Also Apollo 6 lost a SLA adapter panel...
>> There was some suspicion that the adapter-panel failure might have been
>> due to the first-stage Pogo, but investigation showed that it was in fact
>> an independent failure.
>
>I didn't know that! If it wasn't the pogoing that caused the panel to
>fall off, what was it?

There was considerable suspicion about that because the panel failed --
I think only its outer skin came off, not the whole panel, although it's
hard to find a clear description -- at around the time of the Pogo.  But
it turned out to be unrelated.

The problem was that the adapter was a beautifully made metal honeycomb
structure, and apparently it hadn't occurred to anyone that the gas in the
honeycomb cells would get hot and expand during ascent.  That particular
panel may have been a bit on the weak side or even had a manufacturing
defect, which would explain why it was the only such failure seen, but the
problem was more fundamental than that.  The fix was a layer of insulation
(cork) on the outside of the adapter panels, plus vent holes to prevent
pressure buildup in the honeycomb cells.

Incidentally, this is a good example of why you can't read just one book
on the subject of Apollo and know it all. :-)  The above is my synthesis
of brief accounts -- all slightly different -- in three or four books,
discounting another half-dozen which had nothing useful on the matter.

(Better still to go to the original documents, but that's both physically
difficult and extremely tedious.)
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu

Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Apollo brush with potential disaster ?(was merits of STS)
Date: Wed, 14 Jan 1998 16:00:07 GMT

In article <34BC402F.7B13@tassie.net.au>,
Justin Wigg  <jjwigg@tassie.net.au> wrote:
>...Also Apollo 6 lost a SLA adapter panel, failed it's J-2 restart
>test, entered the wrong orbit and suffered from wild engine gimballing
>in *trying* to get to the right orbit...

Well, it wasn't quite *that* bad. :-)  The J-2 restart failure was due to
the same problem that caused the engine shutdown during ascent.  The wrong
orbit and the interesting steering history (not really "wild gimballing")
were simply the result of the guidance system trying to make the best of
a bad situation after losing two engines; they weren't really failures.

There was some suspicion that the adapter-panel failure might have been
due to the first-stage Pogo, but investigation showed that it was in fact
an independent failure.
--
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         | henry@zoo.toronto.edu