Wife Mary Haise and NASA astronaut Jerry Carr monitor the mission. Photo: NASA/JSC

The human problems are as big as the technical ones. For instance, the vital mid-course correction: Without it, Apollo 13 would have missed the earth by 10 miles. And was done manually. Jim Lovell and Fred Haise had to be most rested to tackle the split-second button-punching involved.

That's why you've been hearing Mission Control chaffing the crew, saying: "Why don't you guys stop worrying and get some sleep?"

Then the re-entry itself. The immediate future of America's manned space programme depends on the astronauts photographing the damaged Service Module as it is jettisoned. How far should Mission Control hazard their safety - for they'll be pretty hard-pressed at that stage - by asking for photographic activities as well?

I saw Dr Tom Paine, head of NASA, in the canteen just now, wearing dark glasses. He's the man they are all going to for final decisions. He's had the job, too, of comforting the wives during their long ordeal.

Marilyn Lovell and Mary Haise, with their six children, live five miles down the road from here. Dr Paine's been to see them because they are not sleeping much, but listening continuously to their private feed from Mission Control. The astronauts' wives have developed a way, at times like this, of drawing together in a tight group. Neil Armstrong, the first man on the moon and a neighbour of Mary Haise, who is expecting her third child in June, keeps popping in with reassurances as well.

Watching it all going on, I'm finding it hard to believe: all this brave and incredible improvisation -- and of course the enormous courage of the astronauts.

It's sad that the one big success of the mission has gone almost unnoticed: the extraordinary four-hour seismometer readings that followed when the 15-ton, third stage Saturn rocket crashed into the face of the moon.