New simulation of the Apollo 13 explosion. Photo: Analytical Graphics, Inc.

Big trouble for Apollo 13 -- so serious that there's talk of having to use the Lunar Module as a lifeboat to help get the crew back to Earth.

Trouble struck with master alarms warning of power failures soon after 4 am British time [10 pm Houston time, 6 hours earlier]. Since then, there've been hectic exchanges between Mission Control here and the spacecraft, trying to get things right.

So far, no success. At the moment everyone is concentrating on how to get Lovell, Haise and Swigert back home.

Two of Apollo 13's fuel cells have had to be shut down. The spacecraft, over 200,000 miles from Earth, has been told to use as little power as possible.

The crisis came with startling suddenness. A relaxed Mission Control team was about to change shifts after watching a vivid colour TV transmission from inside the Lunar spacecraft. Lovell had been twitting Haise about the way he'd shaved for it; Haise had replied that since it had taken him an hour, that shave would probably he his last.

Lovell signed off from Aquarius, the Lunar spacecraft, and said the crew intended to have a pleasant evening back in Odyssey, the Command spacecraft. "Goodnight" he said. But Houston replied:

"13, we' ve got one more item for you. We'd like you to stir up your cryo tanks. In addition we have shaft and trunnion for looking at Comet Bennett if you need it".

"Okay" replied Lovell, "stand by". Then: "Hey, we've got a problem here!" "This is Houston, say again please" replied Mission Control; and Haise came in: "Houston, we've had a problem. We've had a Main B bus interval...and we had a pretty large bang associated with the caution and warning there. "

I'm told that three loud bags were heard. Lovell reported a red master alarm light had come up on the control panel, that something had gone wrong with the power supply, and that they could see the spacecraft venting.

There have been constant instructions from Houston, telling the astronauts to try various way of restoring the power supplies. So far they've been unsuccessful. They're so far from Earth that the only way they can get home now is to swing round behind the Moon; but at the moment they are not even in a "free return trajectory". To do so they must fire their main engine - but at the moment it doesn't look as if they have the power. As a last resort they can probably use the Lunar spacecraft's engines to get on a circumlunar trajectory which would bring them home.

Hence the talk of using the Lunar Module as a lifeboat. They may have to go into the Lunar Module, fire its engines to get on a course for home, then return to the Command Module for re-entry. The Lunar Module of course has no heat-shield, so it is only of use at the moment for the power its engines provide.