However, Russian mission control denied media suggestions that the astronauts might have to blast off at 11am BST today if they cannot get power. They insisted that there is enough bottled oxygen for five more days, and that the temperature will remain high enough to be tolerable for another two.
If Mir is abandoned, and falls out of orbit, the results could be catastrophic. One expert predicted that large chunks of the station could survive the re-entry into the atmosphere, and come crashing to the ground.
Mir's crew, including British-born Michael Foale, were forced yesterday morning to retreat by flashlight into the Soyuz escape capsule after one of them - Russian mission control would not say which - accidentally pulled out a data cable to one of the main computers.
That led to almost complete power loss, leaving the crew in darkness, without oxygen generators and unable to stop the 70-tonne spacecraft spinning chaotically so that its solar panels could not gather power from the Sun.
The crew is already increasingly exhausted, the result of three weeks living in a spacecraft which has lost more than a third of its power, ever since a mistake while practising docking maneouvres caused a crash on 25 June that holed one of the six modules.
As the crisis broke, the tension among Russian ground controllers, who have been battling with a new problem every other day, was visible. One was heard barking instructions to the commander into a microphone: "Shut it down! Shut it Down!"
The cosmonauts did so, plunging Mir into darkness for half of its 90- minute orbits - the period when it is out of view of the Sun. "This is a kindergarten," fumed Vladimir Solovyov, the Russian Mission Control director, after ending one radio conversation with Mir's crew. Earlier he was heard demanding: "Have you switched everything off? Switch everything off on the left side!"
By yesterday evening, officials were calmer and more confident. Mr Solovyov said Mir's orientation towards the Sun would be restored this morning and the gyrodines system, which keeps the station in the best position to accumulate energy, would be restored tomorrow. "We are not planning to return the crew, we are planning to continue the flight." he said.
But the crisis, the latest in a catalogue of blunders and break-downs, had made its impact. New question marks now hang over the future of Mir, a station that was designed to last for five years but has now operated for 11 - not least because Russia is desperate for the US dollars that it receives for working alongside Nasa.
The American astronaut, Jerry Linenger, who recently returned from a tour on Mir, once told an interviewer there are two words that a cosmonaut dreads: fire and decompression. In the last few months, Mir has had both.
In February, there was a serious fire on board in which one of the escape routes was blocked by molten metal. And on 25 June, the Spektr scientific module - where Mr Foale had his living quarters and laboratory - had to be hastily sealed off after a cargo drone bumped into it, punching a hole in a wall and causing the air to rush out. In the ensuing scramble, power cables running from solar arrays in the module were disconnected, causing Mir to lose almost half its power.
Matters grew still worse this week. As plans were being drawn up for a sortie into the dark, cramped Spektr to find and reconnect the cables, Mir's commander, Vasily Tsibliyev, began to complain of an irregular heart beat. This was not the first sign that tension was beginning to take its toll; officials at his Mission Control revealed he had been repeatedly complaining about overwork and tiredness.
A committee of specialists in Moscow ruled that he had arrhythmia and could not participate in the space walk. While he was prescribed sedatives and rest, attention switched to whether Mr Foale, a 40-year-old astrophysicist born in Lincolnshire, would take his place. Nasa yesterday said he could train for the mission, although it has yet to give him clearance. It is planned for 24-25 July.
While both Nasa and Moscow wonder what to do next, their critics are mustering. Professor Andre Balogh, an expert in space technology at Imperial College, London, yesterday declared that the Mir astronauts should abandon ship. "I think they are in serious danger ... If I was the mission controller I would give the order to evacuate.
"What is happening now is the culmination of two or three weeks' of problems. The impression I get is that it is very serious. It is like a disaster movie, but in real life ... it will almost certainly go out of control if it is abandoned"
"It's big enough, there are pieces that will survive re-entry, the equivalent of two or three Skylabs [The US space station which crashed into Australia in 1980]".
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