WWW.ASTRONOMY.COM 31planned altitude of 100 nautical miles
(185 km) above Earth in a circular park-
ing orbit. Then, some two hours later, the
crew fired engines that set the spacecraft
off toward the trans-lunar injection. As
this was occurring, the onboard crew
and members of the f light crew on the
ground, led by Flight Director Gene
Kranz, analyzed the engine anomaly and
found that it was caused by significant
so-called pogo oscillations. These vibra-
tions caused the engine to shut down and
alarmed the ground crew; they had been
observed previously during the Apollo 6
test mission. The lessons from this f light
led to modifications to avoid these oscil-
lations on later f lights, by adding a
helium gas reservoir to dampen vibra-
tions, an automatic cutoff valve, and sim-
plified propellant valves that the
engineers believed would lessen the
potential problem.
After the typical separation and dock-
ing of the command module and the LM,
the crew had the craft in the proper con-
figuration and cast the spent third stage
engine aside into a lunar orbit. They
cruised moonward, anticipating a
smooth, three-day trip that would carry
them to the geologically interesting area
of Fra Mauro.
Then, a bang
During the cruise phase, some 56 hours
after launch, the crew conducted a live
TV broadcast from the capsule and then,
some six and a half minutes later, began
a variety of tasks. Lovell stowed away
the TV camera; Haise secured the LM;
Swigert was asked to perform a routine
task by the ground controllers. In the
service module, he switched on the tank
stirring fans in holding containers of
hydrogen and oxygen. This periodic
exercise mixed the gases, which were at
very low temperatures, and allowed the
gauges to read the tank contents more
accurately. But some two minutes after
Swigert did so, the astronauts suddenly
heard what they described as a “pretty
loud bang.” On gauges, they then
observed fluctuations in the craft’s
electrical power and the computer-
automated firing of attitude control
thrusters. At first, for a brief two sec-
onds, the spacecraft lost communica-
tions and telemetry with the ground,
but the computer reset the antenna,
restoring communications.
Lovell, Swigert, and Haise were per-
plexed, and momentarily believed the
LM had been struck by a meteoroid.
Scrambling to understand the situation,Lovell uttered the line, “Houston, we’ve
had a problem,” which Swigert also
stated. Lovell believed the problem was
related to an electrical bus, with loss of
electrical power on one of the electrical
circuits. Then, the crew noticed further
alarming troubles. The gauge in oxygen
tank No. 2 read “zero.” Soon thereafter,
two fuel cells failed. Lovell turned
around and looked out the spacecraft
window, seeing “some kind of a gas”
leaking from the capsule out into deep
space. And then, troubling transformed
into deeply alarming: Over the next two
hours, another oxygen tank, No. 1, slowly
depleted its supply of the precious gas, its
gauge lagging downward to zero as well.
The service module suddenly had no life-
giving oxygen gas left.
And if that wasn’t bad enough, the
situation turned grave. The command/
service module functioned by creating
electrical energy from the combination
of hydrogen and oxygen into water, but
when the first oxygen tank depleted, the
only fuel cell still operating also shut
down. This now meant that the craft had
only a very limited supply of reserve bat-
tery power and a small amount of water
left. Scrambling, consulting with the
ground controllers, the team decided toThe farside crater Chaplygin was photographed by the Apollo 13 crew, as their craft came around the Moon, heading straight back toward Earth. Chaplygin is a
76.4-mile-wide (123 km) crater with terraced walls, a smooth floor, and a central peak.