Apollo Expeditions to the Moon|
A TRAGIC FIRE TAKES THREE LIVES
Apollo in January 1967 was adjudged almost ready for its first manned flight in
Earth orbit. And then disaster. A routine test of Apollo on the launching pad at Cape
Kennedy. Three astronauts - Grissom, White, and Chaffee - in their spacesuits in a
100-percent oxygen environment. A tiny spark, perhaps a short circuit in the wiring.
It was all over in a matter of seconds. Yet it would be 21 months before Apollo would
again be ready to fly.
By April 1967, when I was given the Apollo spacecraft job, an investigation board
had completed most of its work. The board was not able to pinpoint the exact cause
of the fire, but this only made matters worse bccause it meant that there were probably
flaws in several areas of the spacecraft. These included the cabin environment on the
launch pad, the amount of combustible material in the spacecraft, and perhaps most
important, the control (or lack of control) of changes.
Apollo would fly in space with a pure oxygen atmosphere at 5 psi (pounds per
square inch), about one-third the pressure of the air we breathe. But on the launching
pad, Apollo used pure oxygen at 16 psi, slightly above the pressure of the outside air.
Now it happens that in oxygen at 5 psi things will generally burn pretty much as they
do in air at normal pressures. But in 16 psi oxygen most nonmetallic materials will
burn explosively; even steel can be set on fire. Mistake number one: Incredible as it
may sound in hindsight, we had all been blind to this problem. In spite of all the care,
all the checks and balances, all the "what happens if's", we had overlooked the hazard
on the launching pad.
The pedigree of just one Apollo
spacecraft took this many books.
A mind-numbing degree of documentation contributed to reliability,
safety, and success. lf one batch of
one alloy in one part was found to
be faulty, for example, a search
could show if the bad material had
found its way into other spacecraft,
to lie in wait there.
Inspecting the new hatch, Wally Schirra makes
sure his crew cannot be trapped as was the
crew that died in the terrible Apollo spacecraft
fire. Opening outward (to swing freely if pressure
built up inside), the new hatch had to be much
sturdier than the old inward-opening one.
The complicated latch sealed against tiny
leaks but allowed very rapid release.
Most nonmetallic things will burn - even in air or 5 psi oxygen - unless they are
specially formulated or treated. Somehow, over the years of development and test, too
many nonmetals had crept into Apollo. The cabin was full of velcro cloth, a sort of
space-age baling wire, to help astronauts store and attach their gear and checklists.
There were paper books and checklists, a special kind of plastic netting to provide more
storage space, and the spacesuits themselves, made of rubber and fabric and plastic.
Behind the panels there were wires with nonmetallic insulation, and switches and circuit
breakers in plastic cases. There were also gobs of insulating material called RTV.
(In Gordon Cooper's Mercury flight, some important electronic gear had malfunctioned
because moisture condensed on its uninsulated terminals. The solution for
Apollo had been to coat all electronic connections with RTV, which performed admirably
as an insulator, but, as we found out later, burned in an oxygen environment.)
Mistake number two: Far too much nonmetallic material had been incorporated in
the construction of the spacecraft.
After the fire, flammability and
self-extinguishment were key concerns.
In the test setup at right
a wiring bundle is purposely ignited,
using the white flammable
material within the coil near the
bottom to simulate a short circuit (left).
Picture at right shows the
aftermath: a fire that initially
propagated but soon extinguished
itself. It took great effort and
ingenuity to devise materials that
would not burn violently in the
pure-oxygen atmosphere. lf a
test was not satisfactory and a
fire did not put itself out, the
material or wire routing was redesigned
and then retested.
Seared at temperatures hotter than the surface
of the Sun, a sample of heat-shield material
survives the blast from a space-age furnace.
Machines used to check out Apollo components
were as demanding as those in the mission itself,
because a mistake or miscalibration during
preflight trials could easily lay the groundwork
for disaster out in unforgiving space.
There is an old saying that airplanes and spacecraft won't fly until the paper
equals their weight. There was a time when two men named Orville and Wilbur Wright
could, unaided, design and build an entire airplane, and even make its engine. But
those days are long gone. When machinery gets as complex as the Apollo spacecraft,
no single person can keep all of its details in his head. Paper, therefore, becomes of
paramount importance: paper to record the exact confiugration; paper to list every
nut and bolt and tube and wire, paper to record the precise size, shape, constitution.
history, and pedigree of every piece and every part. The paper tells where it was made,
who made it, which batch of raw materials was used, how it was tested, and how it
performed. Paper becomes particularly important when a change is made, and changes
must be made whenever design, engineering, and development proceed simultaneously
as they did in Apollo. There are changes to make things work, and changes to replace a
component that failed in a test, and changes to ease an astronaut's workload or to make
it difficult to flip the wrong switch.
Meant to fly in a vacuum, and to survive fiery reentry,
the command module had also to serve as a
boat. Although its parachutes appeared to lower it
gently, its final impact velocity was still a jarring
20 mph. Tests like this one established its resistance
to the mechanical and thermal shocks of impact, and its ability to float afterward.
Hitting land was possible, even though water was the
expected landing surface. For this, a shock-absorbing
honeycomb between the heat shield and the inner shell
was one protection, along with shock absorbers on the
couch supports. A third defense against impact was
the way each couch was molded to its astronaut's size
and shape, to provide him with the maximum support.
Mistake number three: In the rush to prepare Apollo for flight, the control of
changes had not been as rigorous as it should have been, and the investigation board
was unable to determine the precise detailed configuration of the spacecraft, how it was
made, and what was in it at the time of the accident. Three mistakes, and perhaps more,
added up to a spark, fuel for a fire, and an environment to make the fire explosive in its
nature. And three fine men died.
Through the portal of a huge test chamber,
the command and service modules can be seen in preparation for
a critical test: a simulated run in the entire space
environment except for weightlessness. In this vacuum chamber
one side of the craft can be cooled to the temperature of black
night in space while the opposite side is broiled
by an artificial Sun. Will coolant lines freeze or boil?
Will the cabin stay habitable?