The riskiest-ever walk in space

Russian officials yesterday decided that the ailing commander of the damaged Mir space station will not take part in a perilous repairs mission, and made further moves to press Nasa to allow the British astronaut Michael Foale to replace him.

They claimed that Nasa had agreed to allow Foale to train for the operation, which some are billing the most dangerous space-walk ever. But no final decision will be taken until next week.

The trip to reconnect solar panels in the dark, freezing and airless Spektr module has been rescheduled to next Thursday because the commander, Vasily Tsibliyev, has developed heart problems. The module was punctured in a collision with a cargo ship three weeks ago.

The sortie may yet be carried out by a relief crew who are due to dock with Mir on 7 August, but the Russians have made clear that they want to go ahead as soon as they safely can. Mir has been on just over half power since the collision.

However, the Russians appear to be more enthusiastic about using Foale for the mission than their counterparts in Houston. Last night, Nasa said it had not yet agreed to allow him to go on the sortie, or to take part in extensive pre-walk training. "He can do some basic things, but no official simulations or the actual spacewalk - none of that's been approved by Nasa yet," said a spokesman.

The two-man repairs mission had been planned for this week, but was postponed when Tsibliyev, 43, developed an irregular heartbeat, a condition which doctors attributed to tension in the aftermath of the crash. He also complained of tiredness and overwork. Russian press reports say that officials blame him for the accident, the worst in the station's 11-year-history.

A practice run is planned on Monday. Reports here said that afterwards officials in Russia's Mission Control outside Moscow and Nasa's Johnson Centre in Houston will hold a video conference to decide whether Foale should participate. If he does, it will be a first for Britain. Although he is now a US citizen, he was born in Lincolnshire, educated at Cambridge, and is the son of an RAF air commodore.

The chief of Russia's Mission Control, Vladimir Solovyov, said yesterday that Foale was "clearly delighted" by the possibility of taking part in the sortie. Under the initial plans, he was not expected to venture into space during his stint on Mir flight, although he has walked in space before, in 1995.

Under the original plan, Foale was to have spent the operation in the Soyuz escape capsule, ready to launch an emergency getaway if necessary.

If he replaces the commander, then it is likely he will find himself assisting the flight engineer, Alexander Lazutkin, who will enter the module and try to locate wires from three solar panels. These cables, which were unhooked in the scramble to seal off the module after it was holed, will be reconnected to a hatch linking it with Mir.

The crew's task is further complicated by uncertainty over what may be floating around inside Spektr. There is concern that laboratory chemicals may have escaped from their containers and could damage the cosmonauts' equipment.