After two successful missions the American public was starting to take the Moon for granted But when an explosion struck Apollo 13 in April 1970 the world was gripped by the drama

Shortly after launch, the crew of Apollo 13 settled in for a long translunar flight. For this mission, veteran astronaut Jim Lovell was joined by first-timers Fred Haise and Jack Swigert (a late substitute for Ken Mattingly, who had been exposed to German measles). Everything was going well until, some 56 hours into the flight and with the spacecraft already closer to the Moon than the Earth, the crew triggered a routine stir of the CSM's oxygen tanks. There was the sudden thump of an explosion in a vacuum, and the astronauts were alarmed to see pressure in one of the main oxygen tanks dropping and electrical power to the CSM rapidly failing (see over). With masterful restraint, Swigert famously reported "Okay, Houston, we've had a problem here."

In fact, the astronauts and their controllers knew very well that the "problem" was life-threatening. The Service Module was clearly crippled, unable to provide power or oxygen to the Command Module.

PROBLEMS FROM THE OUTSET

Pogo oscillations (see p. 119) caused one of the second-stage engines to cut out during launch, forcing the others to burn longer.

All thought of landing on the Moon was abandoned, but the crew could not simply turn the spacecraft around - the CSM did not carry enough fuel for such a manoeuvre, even if it could still fire its engines. The way back to safety lay in flying onwards and looping around the Moon (see panel, opposite).

The immediate question was how to survive that long. The Command Module had limited batteries and oxygen supplies built into it, but only enough for a few hours of independent existence during and after re-entry - clearly these would have to be preserved.

Fortunately, NASA had a contingency plan to use the LM, attached but dormant at the front of the CSM, as a lifeboat in this kind of emergency. Racing against time, the crew powered up the LM Aquarius, moved supplies into it, and sealed themselves in, switching off nearly all systems on the CSM Odyssey to conserve what little power remained.

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