As Captain James
Lovell, commander of the ill-starred Apollo 13 mission described it:
"Fred [Haise] was still in the lunar module. Jack [Swigert] was
back in the command module [CM] in the left-hand seat, and I was
half-way in between, in the lower equipment bay, wrestling with TV
wires and a camera, watching Fred come on down, when all three of
us heard a rather large bang -- just one bang.
Now, before that ...
Fred had actuated a valve which normally gives us that same sound.
Since he didn't tell us about it, we all rather jumped up and were
sort of worried about it; but it was his joke and we all thought it
was a lot of fun at the time. So when this bang came, we really
didn't get concerned right away ... but then I looked up at Fred
... and Fred had that expression like it wasn't his fault. We
suddenly realized that something else had occurred ... but exactly
what we didn't know."
View of damaged command module
Haise said he felt a
vibration. Up in the CM Swigert reported,
"... about two
seconds elapsed when I had a master alarm and a main Bus 'B'
undervolt [loss of power] ... I transmitted to Houston that we had
a problem (sound clip,
"I guess it's kind of
interesting to know what the feelings of the crew are when
something like this happens. When you first hear this explosion or
bang ... you don't know what it is. We've had similar sounds in the
spacecraft before that were for nothing. ... and then I looked out
the window and saw this venting ... my concern was increasing all
the time. It went from 'I wonder what this is going to do to the
landing' to 'I wonder if we can get back home again' ... and when I
looked up and saw both oxygen pressures ... one actually at zero
and the other one going down ... it dawned on me that we were in
was, if anything, conservative. The bang was the explosion of liquid
oxygen tank #2 in the service module. This tank provided the vital
oxygen used by the fuel cells that were Apollo's primary power
source. There was a backup battery-powered electric supply in the
Command and Service Module (CSM) with a lifetime of up to ten hours,
but Apollo 13, at the time of the explosion, was 87 hours from home.
The serious nature
of the emergency was starkly evident to the crew and Mission
Control. Lovell and his crew mates were more than 200,000 nautical
miles out in space with a dead Service Module, including its main
propulsion engine. The explosion had wiped out the CSM's main supply
of life-sustaining oxygen and power. The CM's 10 hours of operating
life had to be reserved for the approach to the earth's atmosphere
because, of the three components, it alone had a heat shield which
would allow the crew to re-enter the atmosphere and splashdown
The crew's salvation
rested with the Lunar Module (LM), the oddly-shaped spacecraft
designed to separate from the CSM, land two astronauts gently on the
moon, sustain them while there and then carry them back to the
mother ship in lunar orbit. But that mother ship was a partial
wreck, drifting in space, and the LM became the lifeboat.
What followed was an
epic struggle of skilled and highly trained astronauts working in
close coordination with the ground-based team at Mission Control
against the hostile environment of space. For 86 hours and 57
minutes, more than three days, the struggle continued until the
final victory came: Odyssey's trio of orange-striped parachutes
dropped the spacecraft into the gently rolling Pacific Ocean 3.5
nautical miles from the prime recovery ship, the carrier Iwo Jima.
In retrospect, those
looking for omens of disaster could have found a few in the early
stages of the flight. Before launch, a helium tank showed a higher
pressure than expected, and was watched with some concern. A member
of the prime crew, Lt. Commander Thomas K. Mattingly, was exposed to
German measles a few days before launch. Swigert, the backup
crewman, replaced him. A liquid oxygen vent valve refused to close
on the first command, and had to be re-cycled several times before
it would shut.
In flight, the
center engine of the S-11 stage cut off more than two minutes early
and, to compensate, the remaining four engines were burned 34
seconds longer than planned. As a further remedy, the engine of the
Saturn V's third stage was fired for an extra 9 seconds in the
orbital insertion burn. The result was a trivial 1.2 feet per second
velocity greater than predicted.
though, were insignificant. They were typical of the minor anomalies
that launch and flight crews expect to encounter, and are trained to
The flight proceeded
with gratifying smoothness. After Apollo 13 entered the lunar
corridor, the CSM separated from the third stage and manoeuvred to
extract the LM from its housing atop the stage.
The initial trajectory
of Apollo 13 was what is called a "free return" course. If
undisturbed, it would carry the spacecraft behind the moon, out
again, and on a correct course for earth, a safety factor in the
event of a propulsion malfunction. However, the Fra Mauro area
landing site required changing this trajectory to a "hybrid" course
which was not a "free return" trajectory.
Earth as viewed from Apollo 13
The change was
routinely made on the mission's second day. No one knew this
manoeuvre would later complicate the problem of getting the crew
back safely because it would have to be reversed.
astronauts powered up the LM lifeboat, Mission Control set about
mobilizing all the talents available to deal with the crisis. In
addition to the contractor representatives normally assisting with
the flight, the manufacturers of the major systems and sub-systems
in the spacecraft made their top specialists immediately available.
A coast-to-coast network of simulators, computers and experts was
quickly hooked up. The operation was a tour de force of the breadth
and depth of American technological competence.
The problem had two
However, these two
concerns were sometimes in conflict. The guidance platform had to be
aligned. As Lovell later explained it, this was the
- Getting Odyssey
and Aquarius (call signs for the CM and the LM, respectively) on
the quickest course for home.
consumables (power, oxygen and water) onboard.
because without knowing exactly which attitude the spacecraft is
in, there's no way to tell how to burn or how to use the engines of
the spacecraft to get the proper trajectory to come home. "
But activating the
guidance platform drew heavily on the critically short supply of
Cutting back on the
use of consumables was the first order of business. The CM was shut
down completely after Lovell and Haise powered up the LM and made
sure it was functioning properly. Except for the final phase of the
flight, the CM was only used as a bedroom. Later all the LM's
systems except those relating to life support, communications, and
environmental control were turned off, drastically reducing
Aquarius' power consumption. The LM was designed to support two men
for 49.5 hours, but these actions stretched its resources to provide
life support for three men for 84 hours.
power, the first milestone, aligning the LM's guidance platform, was
A Shorter Course
The next step was an
engine burn to return the spacecraft to a free-return trajectory.
Normally, a course correction of this kind presents no difficulty.
For Apollo 13, there were complications. The LM's descent engine,
not the SPS, was doing the pushing this time, and it was pushing a
spacecraft that had a different mass and centre of gravity. After
running the manoeuvre through the computers and simulators on the
ground, Mission Control ordered a burn that added 38 feet per second
to the spacecraft's velocity.
"milestone" as Lovell put it, was cutting the time of the return
leg. As Lovell described the situation:
"The nominal flight
time ... was 153 hours (from launch) if we had done nothing else.
Because consumables were critical, Fred was doing the
back-of-the-envelope type of calculation and he figured, if we were
lucky, we had about one hour of consumables to spare."
To improve this
too-close-for-comfort margin, it was necessary to step up the
spacecraft's velocity. Several velocity changes were possible. The
one which would save the most time would bring the crew down in the
Indian Ocean; a possibility, but recovery would be awkward. A second
option would reduce the return time from 153 hours to 143 hours and
bring the spacecraft in to the Pacific as planned. However, this
option required a velocity increase of 860 fps. Mission Control
called the rocket specialists at TRW Systems to determine whether
the LM's descent engine could do it.
The descent engine
can operate for 17 minutes. Engineers at TRW Systems had test-fired
Aquarius' engine and were confident it was good. The tests had also
given them a useful reading on its performance. Nevertheless, they
went to the simulators and computers to make sure, and the findings
confirmed that the engine could do the job with plenty to spare.
Thus reassured, Mission Control worked out the procedures and
relayed them to the crew.
The engine was
fired, the manoeuvre successfully executed, and everyone breathed
The accident and its
effects kept Mission Control, its teams of experts, and the
simulators and computers busy for most of the return leg. Course
corrections and new detailed timelines had to be worked out.
Manoeuvres had to be recalculated to use a minimum of power and
water (for cooling equipment). How would the linked LM and CM behave
after the SM had been jettisoned? What would be the effect of
discarding the LM one hour before re-entry?
Questions of this
kind were put through the various simulator-computer complexes until
the ground team was certain that all possibilities had been checked
out, and the best answers were in hand. Astronauts Alan Shepard and
Ed Mitchell operated one of the LM simulators at the Manned
Spacecraft Centre in Houston and Gene Cernan and David Scott worked
in the other. At Cape Kennedy, Astronaut Dick Gordon simulated
emergency procedures in a third LM. One team of simulator
specialists worked around the clock without a break. No procedure,
no manoeuvre instruction, no checklist was relayed to the crew that
hadn't been thoroughly proved out.
A Cold Ride Home
The ride home was a
cold one. With the systems in the CM shut down, there was no
internal heat source to maintain cabin temperatures. The inert CM
settled to a level of 38 degrees F, so cold that the crew stopped
using the couches for their sleep periods. They made makeshift beds
in the LM, which was warmer than the CM but still uncomfortable.
Worse than the discomfort, the cold prevented them from resting
well, and Mission Control was concerned that fatigue might impair
their ability to function.
Ingenuity At Work
Many of the
difficulties that arose on the return were solved by "jury rigs"
that were marvels of ingenuity. The atmosphere in the spacecraft
cabins is "washed" of carbon dioxide (produced by the crew's
exhalations) by canisters of lithium hydroxide. The LM's canister
system overloaded and the carbon dioxide in the cabin atmosphere
began a potentially dangerous rise.
"Jury Rigged" Canisters to Clean Air of Carbon Dioxide
After studying the
problem, Mission Control instructed Lovell to make an adapter that
would attach a hose to the lithium hydroxide canisters in the CM so
they could help purify the air. Lovell went the ground one better by
splicing together two hoses so the rig would reach through the
docking tunnel into the CM. Within an hour carbon dioxide levels
The new re-entry
procedure called for two course corrections, the first to get the
spacecraft more toward the centre of the re-entry corridor and the
second to refine the angle of entry which had to be between 5.5
degrees and 7.5 degrees. Without the guidance platform powered up,
the normal method of determining the attitude of the spacecraft
would be by taking star sights. However, ever since the explosion in
the SM, the spacecraft had been shrouded in a cloud of debris that
glittered in the sun and made sighting on a star impossible. A
technique worked out during Apollo 8, using the earth's terminator
and the sun, was used. Lovell recounted his reaction at a
post-flight press conference:
The burn made the
desired refinement to a re-entry angle of 6.49 degrees.
"When the ground
read out the procedure to us, I just couldn't believe it. I thought
I'd never have to use something as way-out as this. And here I was
on Apollo 13, using this very same procedure. Because it was a
manual burn, we had a three-man operation. Jack would take care of
the time. He'd tell us when to light off the engine and when to
stop it. Fred handled the pitch manoeuvre and I handled the roll
manoeuvre and pushed the buttons to start and stop the engine."
Six and a half hours
before re-entry, ground-based studies showed that the three CM
batteries, two of which had been re-charged from the LM, did not
have enough power to maintain all the CM systems throughout
re-entry. After intensive simulation on the ground, Mission Control
relayed a phased power-up sequence to the crew in which all the
needed systems were up only 2.5 hours prior to re-entry, well within
the capacity of the storage batteries.
On the final phase
of the return leg, as Lovell later put it,
getting better all the time."
But the crew's troubles
were not at an end. Lovell summed up their situation after the
"We were in a
different situation now, because, normally when you come home you
have only the CSM ... now, though, we had a dead service module ...
a command module that had no power ... a lunar module ... a
wonderful vehicle ... but that didn't have a heat shield and
shortly we'd have to abandon it.
Discarding the SM
"Our procedure ... was
to make sure we had a good angle of entry and then at about 4.5
hours before re-entry to manoeuvre to a position to get rid of the
Swigert told the
newsmen of the jettisoning.
"... the ground had
read up a very nice timeline. The only nervous moment we had ...
normal procedures require arming the logic busses [the pyrotechnic
system that explodes the SM away] and letting Houston look at all
the relays. At this time, we didn't have any telemetry with Houston
and Fred came up and I said ... 'Fred, I'm all ready to jettison
the service module ... just getting ready to arm the pyros.'"
The crew's inspection
of the SM from a safe distance disclosed that a whole panel of the
SM housing, 12 feet high and 5.5 feet wide, near the high-gain
antenna, had been blown off by the explosion.
"Fred said, 'I'll
get a go from Houston.' I said, 'Fred, we don't have any telemetry
with Houston so you're just going to have to put your fingers in
your ears and stand by."
" ... so I armed
the 'A' system and I could hear the relays ... and nothing happened
[an encouraging sign] ... and I armed the 'B' systems and nothing
happened ... so I kind of felt we were home free."
"The procedure went
well -- we used a push-pull method ... Jim and Fred were in the LM
and using the translation controller to give us some velocity. ...
when Jim yelled 'Fire!', I jettisoned the service module and it
went off in the midst of a lot of debris, which is usual."
An hour and a half
before re-entry, the LM "lifeboat" that had been their salvation was
discarded. Mission Control radioed,
and we thank you."
Apollo 13 Lunar Module
"She was a good
Clear of the LM, in
Swigert's words, Odyssey "came on in" to the most accurate landing
in the history of manned space flight.
Recovery of Crew After Splashdown
By a matchless
display of tenacity, resourcefulness, ingenuity and courage, a
determined group of men at Mission Control working closely with a
cool, expert crew averted catastrophe and brought the astronauts
through a brush with death.
As an aborted
mission, Apollo 13 must officially be classed as a failure, the
first in 22 manned flights. But, in another sense, as a brilliant
demonstration of the human spirit triumphing under almost unbearable
stress, it is the most successful failure in the annals of space