The moon. Photo: NASA/JSC

Apollo 13 has achieved the first step necessary for a safe journey home. Jim Lovell, the Commander, successfully fired the Lunar Module's descent engine: a 30 second burn that added 43 mph to the spacecraft's speed of 3,500. Now they are in what's called a "free return trajectory". If no further rocket firings are possible, the craft will pass round the back of the moon and return to Earth, probably on Saturday.

It's planned to make a further burn behind the moon speed up the journey, so that splashdown may be either 9.13 am in the in the Atlantic on Friday morning, or 6.13 pm in the Pacific. The slower journey is preferable, because that's where the main recovery fleet of ships and aircraft is stationed.

The experts here are busy trying to work out what happened. Either a meteorite hit the Service Module, which contains the oxygen tanks and fuel cells, or some other violent event took place in it. Had the accident occurred when the Command and Lunar spacecraft were separated, it would have been impossible for the astronauts to survive.

It's being said here that their chances of returning are excellent, so long as nothing happens to affect the Lunar Module systems. Lovell Haise and Swigert are so dependent on those systems that they will need the oxygen, water and battery power from the LM until perhaps as late as 15 minutes before re-entering the earth's atmosphere.

They will jettison the LM, now their life-raft, at the last possible moment before shutting themselves inside the dead Command Module with its protective heatshield for the final re-entry.

Deke Slayton, the astronauts' boss, has telephoned the wives of Lovell and Haise to explain to them what has gone wrong. Swigert is unmarried.

Mission Control has now advised the crew on all the possible steps they can take to economise in the use of power. One of them is to control the spacecraft's attitutude manually while the other two try to get six hours' sleep. I gather they've sufficient oxygen for six days, but only enough power for four.