4.3.2 Apollo 13
The third manned mission that was intended to land on the Moon was Apollo 13, launched on 11 April 1970. While still on their way to the Moon, about 300 000 km from Earth and almost 56 hours into their mission, the crew heard an explosion coming from one of the oxygen tanks inside the service module. This prompted one of the most famous Apollo quotations, uttered by astronaut Jack Swigert: ‘Houston, we’ve had a problem here’.
The fuel cells which powered the spacecraft needed oxygen to combine with hydrogen to generate electricity and water; with the ruptured oxygen tank losing its contents to the vacuum of space, the main power supply to the command module soon ran out, leaving only the limited-supply back-up batteries to provide power. The crew were forced to shut down the main command module and instead rely on the lunar module, which was able to act like a lifeboat.
With the planned Moon landing now out of the question and the spacecraft rapidly approaching lunar orbit, the crew and mission controllers back on Earth faced a stark choice: either opt for a direct return to Earth, which would mean jettisoning the crew’s only source of life-supporting resources – the lunar module; or try to use the Moon’s gravity to ‘fling’ the damaged spacecraft back towards Earth. Although it would mean travelling further away from Earth first, passing behind the Moon, the latter option was chosen.
With dwindling oxygen supplies and reduced power, which left the inside of the spacecraft at a chilly 4 °C for the duration of the return flight, Apollo 13 limped back to Earth, safely splashing down in the Pacific Ocean on 17 April 1970.
As the crew had proved, returning to Earth could be a perilous experience.