On Wed, 23 Jun 2004 18:28:37 -0400, Matt Whiting
wrote:

Richard Lamb wrote:


In the aftermath of the Apollo 1 fire, NASA took a year (and $75 mil)
to redesign the space craft, mature their mental attitudes, and yes,
did come back with a much safer vehicle.

Yes, but I still wonder how anyone in their right might would use a
nearly pure oxygen atmosphere in a vehicle full of humans and electrical
equipment...

Just got done reading _Angle of Attack_, the biography of North American VP
Harrison Storms, who led the NA Apollo program. Since he got fired
(actually, transferred to headquarters) as a result of the Apollo I fire,
it goes into the situation with considerable detail.

Early in the life of the program, the decision as to what to use for air in
the cabin fell to two basic issues: The known fire danger of a pure oxygen
atmosphere, and the fact that equipment did not then exist to sense and
maintain a nitrogen/oxygen atmosphere.

Other than the CO2 scrubbers (needed with either scheme) all that would be
necessary for the pure-oxygen system would be a simple valve allow oxygen
into the spacecraft when the pressure dropped. With 5 PSI pressurization,
occupants have the same partial pressure of oxygen as at sea level, and the
fire danger isn't too severe. There was the rather low danger of the 5 PSI
pure 02 system, vs the potential schedule risk of the control system and
the known weight penalties of the 14 PSI N/O2 mix. North American favored
the normal-air mix, but the ultimate decision was NASA's.

Also in their proposal, North American specified an outward-opening hatch
with an explosive device to get rid of it in a hurry.

Two things worked against this part of the design. First, NASA had gained
a considerable black eye with the loss of Gus Grissom's Liberty Bell 7.
Whether you believed that Grissom blew the hatch himself or a technical
fault caused the mechanism to fire, the basic fact was that the accident
would not have happened if an emergency eject mechanism had not been
installed.

And...according to _Angle of Attack_, the NASA manager in charge of the
Command Module program was ex-Navy. An ex-Navy submariner, in fact. And
anyone wearing dolphins will insist that pressure on a hatch should cause
it to close *tighter*. He was dead-set against an outward-opening hatch,
and his background also gave him a negative view of things like explosive
hatches.

After all, the main danger was a loss of pressurization on orbit. Either
way the hatch worked, the astronauts would be able to open it in the case
of a pad emergency. But if a hatch failed once the rocket was in orbit,
the astronauts would be dead. An inward-opening hatch was obviously less
risk, on-orbit.

So... Apollo was directed to make the hatch open inward, to not include an
emergency jettison function, and to use a pure-oxygen atmosphere (IIRC, the
pure-oxy atmosphere was NASA Change Order #1). Mercury and Gemini had used
100% oxygen systems, and no problems had occurred.

Then came the Plugs-Out test of Apollo 1.

The Plugs-Out test was basically a full test to see if all the spacecraft
systems would support launch. The crew was in place, the hatch would be
closed, the capsule would be pressurized, and all the umbilicals normally
used to connect the capsule to the pad would be disconnected.

Unfortunately, the test required the capsule to be pressurized to ensure
that everything sealed properly. Since it was on the ground, not in space,
they had to pressurize it to about two PSI over ambient. And, of course,
they used the only breathable gas aboard: 100% oxygen.

A pure-oxygen atmosphere at 5 PSI has its dangers, but a pure-oxygen
atmosphere at 16 PSI is pure horror.

No one really knows what started the fire. What I found interesting is
that the capsule wasn't completely ready for flight...some items were still
in work. For instance, one piece of cabin equipment had been removed for
repair. Its power connector was left in place, energized. It was located
in close to the area where they determined the first started: near one of
the astronaut's feet.

But whether the cause was a kicked connector, scraped insulation, or any of
the myriad other possibilities, a fire started. The crew started the
painful, awkward process of opening the inward-swinging hatch. But within
about ten seconds, the fire had built the internal pressure to the point
where the hatch could *not* have been budged...either by the crew, nor by
any of the pad support personnel with the equipment they had available.

After I read _Angle of Attack_, I re-watched the Apollo 1 fire episode of
HBO's series, "From the Earth to the Moon." The series shows Frank Borman
testifying to Congress about the fire. I don't know if the dialog used in
the series was directly from Borman's actual testimony, but one line really
rang true:

"The cause of this accident was a failure of imagination."

Everyone worried about what would happen during a failure in space, but
nobody thought about the mundane problems that might occur during a simple,
routine pad test...or how a chain of seemingly logical design decisions
could result in disaster.

Ron Wanttaja