A bright-rayed crater on the lunar farside photographed by the astronauts during their pass around the Moon. Photo: NASA/JSC

Apollo 13, safely around the moon, and steadily speeding up as it approaches earth, still faces many problems before it can be regarded as out of trouble.

One is that no one knows, and there's no way of finding out, whether the Command Module's hetshield was damaged when the impact, or explosion, occurred in the Service Module, which is immediately behind the heatshield. But Deke Slayton, obviously very tired but at the same time quietly optimistic, has just been telling me that there's no reason to think it is damaged.

He estimated that a total of 50,000 to 100,000 technicians spread around the United States are at present working flat out developing techniques never tried before to bring Jim Lovell, Fred Haise and Jack Swigert home. All the simulators here are fully occupied, practising the re-entry now due in little more than 24 hours.

The Service Module will be jettisoned first. Then the question is: How long can the Lunar Module, with its power and oxygen supplies, be safely retained? It's planned to use the pressurisation in the docking tunnel to push its 30-ton bulk gently away as late as possible, so that the Command Module's re-entry path won't be affected.

Ken Mattingly, the displaced CM pilot, who never did develop measles, is one of those in the simulator here working out how to get his fellow astronauts back. Deke Slayton, in his own jargon, put it like this: "We're in good shape right now; but you can't count that something else won't crap out on us before they get home"!