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From: (Henry Spencer)
Subject: Re: Apollo 13 Consequences
Date: Wed, 13 Dec 1995 04:58:26 GMT

>What design changes were made to the Saturn V after the Apollo 13 mission? 
>Did e.g. later missions have adapters for the CO2 filters? Did the life  
>boat scenario become an option for other flights or was it considered a  
>once ever event?

Nothing much on the Saturn V, but the Apollo spacecraft had some changes!

First and foremost, they redesigned the interior of the oxygen tank to
prevent a recurrence, putting the wiring inside stainless steel rather
than Teflon.

Second, they added a backup oxygen tank and a backup battery, on the other
side of the SM where another tank explosion wouldn't take them out.  This
made it possible for the SM to limp home without fuel cells or the main
oxygen supply.

Third, they revised a lot of procedures, and adopted a rule that nobody
was allowed to say "that's ridiculous, it can't happen" to the people
designing training simulations.

And yes, I believe they did include some sort of official adapter for
the lithium-hydroxide CO2-removal canisters.
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |

From: Henry Spencer <>
Subject: Re: Apollo 13 re-entry.
Date: Thu, 14 Mar 1996 04:20:09 GMT

> My research into Apollo 13 has not yet answered this question,
> Why did the re-entry take longer than expected?  This is puzzling considering
> that the Apollo 13 splashdown was one of the most accurate in the program.

Don't take the movie too literally.  The length of the blackout period
wasn't that predictable; there was considerable variation.  Apollo 13's
was unusually long but not remarkably so.
Space will not be opened by always                 |       Henry Spencer
leaving it to another generation.   --Bill Gaubatz |

Subject: Re: Duct Tape is Magic (WasRe: Apollo 12 dust)
From: Henry Spencer <>
Date: Jan 25 1997

In article <5c816p$>,
Michael Swartzbeck <sinkers@radix.nut> wrote:
>...If not for duct tape, Apollo 13 would sure have been 
>lost. How else could they have made that CO2 scrubber filter bypass box?
>Yer pal, Mike, who, in retrospect, wonders why the hell
>               they didn't think to make the CM and LEM
>               scrubber filters compatible...

Organizations, like algorithms and structures, have characteristic failure
modes.  The characteristic failure mode of organizations which try very
hard to anticipate all possible failures is that they come to believe that
they *have* anticipated all possible failures.  As a result, they put a
low priority on making their systems versatile and robust, which is what's
needed for coping with *unanticipated* failures.  And there are always
unanticipated failures...

The story of Apollo 13, from beginning to end, is a steady stream of hasty
improvisations to cope with unanticipated problems and to work around the
limitations and lack of robustness of the hardware and procedures.  The
CO2 scrubber cartridge problem was just the most obvious one; there were
plenty more.

Mind you, not quite everyone made this mistake.  Doc Draper at MIT
insisted, flatly and unconditionally, that the CSM and LM navigation
systems and computers would be identical.  He absolutely refused to
customize the two for their specific jobs, even though this meant extra
hassles for him (negotiating with two sets of spacecraft designers
simultaneously).  Understand, we're not just talking about *similar*
systems -- the navigation systems were literally identical, fully
interchangeable, practically the only parts that *were* interchangeable
between CSM and LM.  Which is why the LM navigation system could guide
Apollo 13 home from the Moon...
"We don't care.  We don't have to.  You'll buy     |       Henry Spencer
whatever we ship, so why bother?  We're Microsoft."|

From: Henry Spencer <>
Subject: Re: Apollo 13 movie
Date: Thu, 23 Oct 1997 12:14:01 GMT

In article <62mf3s$2b8$>, Markus Mehring <> wrote:
>>although in several places they fudged a bit for dramatic effect or
>>to compress complex subplots (for example, many of the events on the
>>ground involved more people than the movie suggested), and they
>>inevitably got details wrong here and there.
>And those were?

There's actually a list of them around somewhere.  The one I happen to
remember is that the Saturn V ascent is rather too fast -- somebody had
watched too many shuttle liftoffs and not enough real Saturn V ones.
Pity, given that they made a considerable effort with other details of
that sequence.
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        |

From: Henry Spencer <>
Subject: Re: Apollo 13 movie
Date: Thu, 23 Oct 1997 15:49:29 GMT

In article <62m8eb$>,
Bob Provencher <> wrote:
>Yes, that bothered me also.  It seems that Hollywood always needs a villian
>or _someone_ to potray a little negatively, as they did with the Grumman guy
>and the relationship between the 2 original crew members and the replacement

Also, despite the movie, when Jack Swigert was hastily run through a fairly
elaborate set of readiness-test simulations, he passed with flying colors.
Unlike some other members of backup crews, he'd worked hard.

>...In the beginning when the one guy suggested
>shutting down the two fuel cells.  Was that a mistake and is that what
>caused them to have to move to the other module or was it inevitable no
>matter what they did?

It was inevitable.  The vague hope was that the leak might be in the fuel
cells, and that by shutting them down it might be possible to limp home on
the third cell.  But the leak was upstream of there, as folks were already
guessing, and shutting down the two cells made no difference.  Those cells
were already dead, in fact; deliberately shutting them down just made it
official and irrevocable (thereby officially aborting the mission).

>One part I liked was the part where Lovell had to do some calculations to
>move into the other module.  He does it on paper and the guys on the ground
>all check it with thier slide-rules <g>...

This was actually a minor goof, since he was supposedly doing addition,
and conventional slide rules can't add.  If memory serves, there was at
least one occasion when the folks on the ground were checking the crew's
arithmetic, but they were doing it manually just like the crew.

>...It also gives you a feeling
>of the era and the type of equipment they where dealing with.  I wonder how
>much memory the computers onboard Apollo 13 had???

Numbers aren't ready to hand, but it was trivial by modern standards.
Some of the last Apollos carried Hewlett-Packard pocket calculators as
backup computers.  (They couldn't do everything the main computers could,
but that was more a matter of no peripherals and limited software effort
than limited computing capability.)
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        |

From: Henry Spencer <>
Subject: Re: How did the U.S. beat Russia to the moon?
Date: Fri, 21 Nov 1997 17:49:33 GMT

In article <651ubq$4ka$>,
Sherwood Harrington  <> wrote:
>: both Apollo 6 and Apollo 13
>: came within a hairsbreadth of spectacular launch failure
>Can you expand on this, Henry, or cite some references?  Fascinating.

Apollo 6 is well documented:  two adjacent engines out on the second stage
was then considered unsurvivable, certain to send the stage violently out
of control and require its destruction.  Even after Apollo 6, the Saturn V
manual continued to list such a situation as "possible loss of control".
It was a close shave.  See Murray&Cox, for example.

Apollo 13 is a lot harder to find information on, because the Saturn V
problem was overshadowed by later events.  The second-stage center engine
did not shut down early on a random whim.  It shut down early because it
had gone berserk, with the most violent Pogo oscillation ever seen, and
quite by accident the violent pressure oscillations in its chamber tripped
a "low chamber pressure" sensor and the computer shut it down.  In the
second or so before the shutdown, two tons of engine, solidly bolted to a
massive thrust frame, was bouncing up and down at 68G, flexing the frame
three inches at 16Hz.  Had this continued, it surely would have either
torn itself off its mounts or broken the thrust frame, and either event
would have wrecked the second stage.

Center-engine Pogo had been seen before, in a much milder form, on Apollos
11 and 12, and a fix was already in the pipeline.  Retrofitting it to
Apollo 13's already-stacked booster had been deemed too difficult and not
very important.  Later Saturn Vs had the fix and the problem did not recur.
(This was another reason why the problem didn't attract more attention --
it was considered solved by the time it occurred!)

Documentation on this is scarce.  The only good account I've found is in a
survey article on Pogo in the Spring 1992 issue of Threshold, which is/was
a Rocketdyne internal publication.
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        |

From: Henry Spencer <>
Subject: Re: Apollo 13 second stage shutdown (Was: Re: How did the U.S. beat 
	Russia to the moon?)
Date: Sun, 23 Nov 1997 19:44:57 GMT

In article <6551o1$>,
George Herbert <> wrote:
>>[Apollo 13 engine shutdown]
>Eouch.  I'm suprised that this isn't better documented,
>as it sounds like it was as close a call or closer than Apollo 6 had...

Indeed so.  I've been quite surprised, now that I know what to look for,
at how little mention it gets.  Mind you, nobody has ever done a good
*technical* history of Apollo/Saturn...

>>Center-engine Pogo had been seen before, in a much milder form, on Apollos
>>11 and 12, and a fix was already in the pipeline...

To elaborate on this...  The pre-13 center-engine Pogo was considered a
worrisome nuisance but not an urgent threat.  What was not understood at
the time was that a cavitating turbopump can be a tremendously powerful
amplifier for pressure disturbances.  The earlier center-engine Pogo was
not quite strong enough to drive the engine's LOX pump into cavitation, so
the chamber pressure oscillation stayed small, about 10psi peak-to-peak in
a 780psi chamber.  On 13, the pump cavitated... and the oscillation reached
500psi in about 3s.

>>Documentation on this is scarce.  The only good account I've found is in a
>>survey article on Pogo in the Spring 1992 issue of Threshold, which is/was
>>a Rocketdyne internal publication.
>I don't suppose you would be willing to copy the article? 8-)

I'd be willing to copy it for serious historians who can't get a copy
otherwise, but I don't run a copy shop. :-)  Folks who are seriously
interested would be well-advised to see if they can find a copy of that
issue of Threshold -- it has other Saturn-related stuff in it too.
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        |

From: Henry Spencer <>
Subject: Re: Apollo 13 film.
Date: Mon, 16 Feb 1998 06:18:10 GMT

In article <6bg4nk$79u$>,
Richard Glueck <> wrote:
>In an interview on PBS, Lovell said that they never objected to Swigert in
>the crew, and though they were disappointed in the crew switch, Jack was a
>fully qualified and competant astronaut, and they had complete faith in
>all aspects of his participation.

As I've mentioned before, the movie really does Swigert a serious
injustice -- in particular, the results of his simulation testing after
the crew switch was proposed are 180 degrees wrong, as in fact he passed a
fairly gruelling series of tests with flying colors.  (Some of the other
backup-crew astronauts slacked off, but he worked hard.)

The one problem, which Lovell probably didn't go into to keep his answer
short, would have been crew coordination.  A good bit of the training,
especially the big simulations, is not directed at getting the individual
astronauts competent, but at getting them to work together smoothly and
automatically, so that when a crisis comes, they react as a *team*, with
no fumbling or confusion about who does what.  This degree of coordination
isn't something that can be fully re-established in a few days after a
last-minute crew switch.

One of the later Apollo flights ran into a similar problem with illness
among the crew, and dealt with it more sensibly, by just postponing the
flight a month to the next launch window.  As I recall, Slayton said that
in retrospect, they should have done that on 13 as well.
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         |

From: Henry Spencer <>
Subject: Apollo safety (was Re: Aerospike engine...)
Date: Fri, 27 Feb 1998 16:15:06 GMT

In article <6d6cqe$>,
Cathy James <cjames@fngdev8fngdev8:0.0> wrote:
>	Do you believe that the redesigned post-13 Apollo CSM
>would have survived a 13-style failure/explosion after jettisoning
>the LM?

It seems likely; that's precisely what the redundant oxygen supply and
batteries were for.  Apollo 13 had a lot of problems, but most of them
(with the exception of oxygen supply) boiled down to not having power in
the CSM.
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         |

From: Henry Spencer <>
Subject: Re: Translunar abort
Date: Sun, 29 Mar 1998 23:16:32 GMT

In article <6fgbca$qsb$>,
 <Frank_O'> wrote:
>> Approximately where during translunar coast was the
>> "point-of-no-return", that is, that you could no longer make an abort
>> and go back "in front of" the moon ?
>There were two opportunities for aborts soon after TLI. The first was at
>TLI+90 minutes...  The second opportunity was at 8 hours after liftoff...
>Presumably, any problems occurring after that (say, for example, your oxygen
>tank exploded.....) you would go around the moon...

No, direct "in front of the Moon" abort was still an option until quite
late.  There was some early debate about using a direct abort for Apollo
13, in fact.  The tank failure happened just after Kranz got a routine
notification that the spacecraft was approaching the point where direct
abort was no longer possible, but on paper it was still feasible and it
would have been quicker.  However, it was getting pretty difficult, and it
meant a big burn on the SM engine *after* jettisoning the LM to lighten
ship.  Nobody was sure the SM engine was still available, and nobody but
nobody wanted to cut the LM loose when they might need it badly soon.
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         |

From: (Henry Spencer)
Subject: Re: Apollo 13 Service Module ...
Date: Sat, 19 Jun 1999 23:09:18 GMT

In article <>,
Matt Garrett  <> wrote:
>Something that's always plagued me is why the Service Module
>was kept attached to the CM after the accident.  The CM was
>shut down completely during the free return, so the hi-gain
>antennae wasn't used (was it?), nor was the oxygen since it
>vented and they were unwilling to use the SPS engine.  So
>why keep it?  It seems that the SM was simply dead weight.

It was dead weight, and there was discussion of jettisoning it, which
would have permitted a faster return.  However, the Apollo heatshield did
not cope terribly well with temperature extremes -- the "rotisserie mode"
thermal spin was for the benefit of the exposed parts of it -- and getting
rid of the SM would have meant exposing areas that were never meant to be
exposed until reentry time, and hence did not have the silvery outer
coating which helped protect it.  Since it seemed possible that the
explosion might have damaged the heatshield already, protecting it was
deemed very important.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Apollo 13 Service Module ...
Date: Sun, 20 Jun 1999 18:59:17 GMT

In article <>,
Karl D. Dodenhoff <> wrote:
>I always thought that the idea of keeping the SM attached to protect the
>heat shield seemed odd.  If the heat shield really WAS cracked, I doubt
>the crew would have survived reentry - I figured they'd probably have a
>burn-thru and get fricassed...

A crack wouldn't necessarily be fatal, since the ablation process can seal
small cracks before they can leak.  (The Apollo heatshield was not a
homogeneous slab -- it was ablator filling the holes of a fiberglass
honeycomb -- so a large crack would be difficult to arrange.)

They were more concerned about the possibility that temperature cycling in
space might worsen localized damage in some way.  There wasn't any urgent
reason to risk it.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Apollo 10 / 13 SM
Date: Sat, 21 Aug 1999 23:22:33 GMT

In article <nFmv3.4043$1a1.200525@elnws01>,
Gregory Beat <> wrote:
>Apollo 13 was said to have flown the oxygen tank # 2 that was originally
>assigned for Apollo 10.   If this did occur (damage?), did they just swap
>out oxygen tank # 2 or did they switch the entire SM ??

Neither. :-)  They swapped the oxygen shelf -- a subassembly comprising
both tanks, associated bits of plumbing and hardware, and the structural
shelf that carried them.

(The shelf was installed in Apollo 10's SM, but had to be removed for
minor modifications, and a procedural error caused it to be dropped two
inches during removal.  So it was grounded pending testing, and a fresh
one was used on Apollo 10.  Testing indicated that the dropped shelf had
not been damaged, so it was reinstalled on Apollo 13's SM.  But in fact it
was slightly damaged -- the fill tube in that oxygen tank had been jarred
out of position -- and that plus some other errors led to the accident.)
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Silent death on moon
Date: Thu, 2 Sep 1999 03:38:15 GMT

In article <>,
Graham Nelson  <> wrote:
>> > Also since the CSM had
>> > to be capable of leaving moon orbit with the empty LM ascent stage
>> > attached...
>> This one's a new one on me. Exactly why...
>Its life-support systems (oxygen and power generation, CO2
>removal) or its guidance computer might be needed if the
>corresponding CSM systems failed, as indeed they did on Apollo 13.

Except that Apollo-13-type emergencies WERE NOT CONSIDERED in the design
of the system.  This is established historical fact; it's why there was so
much frantic improvisation during Apollo 13.  (Talk of the "LM lifeboat"
referred almost entirely to using the LM's *engines*, not its life
support.  The Apollo 13 type of accident was deemed both implausible and

Incidentally, most of the LM's oxygen, power, and cooling water were in
the descent stage.  The ascent stage had to exist on its own for only a
few hours, and had only a bare minimum of consumables.

The backup for the CSM guidance computer was a combination of Earth
navigation support and manual piloting.  (Well, more precisely, for the
navigation function, the CSM computer was only a backup.  Piloting
during maneuvers was more important, but could be done manually if it
was really necessary.)

Apollo's fuel margins were generally pretty minimal, to the point where
the mission-planning software gave the planning people an elaborate set of
options for violating official mission constraints slightly to make it
possible to fly the mission within the available fuel.  (Reference on

I'm afraid I'm not going to believe this one without a reference.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: voices (was Re: Did we land on the moon ????)
Date: Thu, 22 Feb 2001 15:41:16 GMT

In article <>,
JF Mezei  <> wrote:
>I also listened to the Apollo 13 "houston we have a problem" audio clip. While
>much of the dialogue is the same as in the movie, I was surprised that in
>reality, they seemed much less excited than in the movie. The voices seemed
>quite calm.

Hollywood overdoes these things.  Most people, especially trained and
experienced people, cope with adversity much more calmly than the movies
would have it.
When failure is not an option, success  |  Henry Spencer
can get expensive.   -- Peter Stibrany  |      (aka

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