However, hours before the launch, mission control announced that the oxygen generators on board the ageing space station had failed - although they emphasised that there was no danger of the three men aboard dying of suffocation.
The two men who were last night en route to Mir, Commander Anatoly Solovyov, 49, and flight engineer Pavel Vinogradov, 43, will have to carry out repairs which are crucial to the entire future of the Russian space programme. Starting on 20 August, one of them will have to undertake a difficult spacewalk inside the cramped, but de-pressurised Spektr module, holed on 25 June by a miscalculation during docking practice with an unmanned supply ship. The intention is to reconnect power cables cut on 25 June when the module was sealed off, and find and patch the leak.
In external spacewalks, the bulky spacesuit is unencumbered by peripheral clutter. By contrast, this will be one of the most complex ever undertaken: even the main part of Mir is only four metres in diameter, and the hole in Spektr is reckoned to lie towards the far end of the module. If floating debris or a wall projection punctures the spacesuit, the cosmonaut inside will die.
The repairs are expected to require six spacewalks, both internal and external.
The importance to Moscow of this mission was underlined by the presence at the launch of government ministers: Baikonur (which Russia is now obliged to rent from its satellite republic) has rarely been the focus of so much official attention since Yuri Gagarin blasted off from there in 1961 to become the first man in space.
There have been some misgivings that financial problems and the repeated technical troubles aboard Mir - which has now racked up a worrying 1,500 malfunctions in its 65,000 45-minute orbits - could mean that these will be the last Russian men in space. Hence the importance of making these repairs to the 11-year-old station - even though Russian authorities have acknowledged that its core will have to be replaced sometime in the next two years.
Since the accident in June, the present crew, Vasily Tsibliyev, Alexander Lazutkin and British-born Michael Foale, have had to manage with reduced power supplies. Those problems multiplied when the Elecktron oxygen generation system broke down again, as it has been prone to do of late.
It sounded dramatic but officials at Mission Control explained there was no cause for alarm as Mir itself was large enough for the existing supply of oxygen to last several days. After that, the astronauts had access to canisters of oxygen which could keep them breathing for a further two months. But the generator should be fixed long before canisters became necessary, they said. The arriving crew will also have canisters available.
The changeover of crew will be a difficult space ballet. First, a Progress supply ship must be undocked from the main capsule, while Tsibliyev and Lazutkin get into the Soyuz TM25 lifeboat. Then the arriving crew on TM26 will dock where the Progress was. The new crew will take over from the old one. Once the two departing Russians embark for Earth in the TM25, the TM26 will be brought around to the docking spot they have vacated. Then the work can begin.
Mission Control decided some weeks ago that the present crew was too exhausted by the constant problems - failing oxygen generators, lack of sleep, variations in temperature caused by failing power generators - to carry out the delicate work. One American astronaut has described doing repairs while wearing a spacesuit as "like doing surgery while wearing boxing gloves".
On one previous occasion, Michael Foale had to abandon a spacewalk when he found he was losing sensation in his fingers, which were freezing. During these spacewalks, he will wait in the TM26 in case an evacuation becomes necessary. Foale's American replacement, David Wolf, is not due to arrive by Atlantis Shuttle until the end of September.
Space professionals are becoming used to crises on Mir, which to the layman sound horrific. On one occasion, the waste disposal system failed, turning the station into an orbiting lavatory, and fire has also broken out on Mir which, when it was launched 11 years ago, was supposed to have a service life of only five years.
Post-Communist Russia, which has not been able to pay its pensioners and state sector workers on time, is desperately short of funds for its once prestigious space programme, which many people now see as a luxury. The outcome of the repair mission will determine whether Moscow's hope of using Mir for two more years is realistic.
Calendar of disaster
February - A fire breaks out on board.
15 May - British born astronaut Michael Foale blasts off on Earth on the the Atlantis shuttle to undertake vital repairs on Mir.
25 June - Mir's airless Spektr module is damaged during a practice docking with the cargo ship. The ensuing collision results in a disconnected cable which ruptures the space module.
Mir is forced to run on reduced power and some areas of the ship are shut down to conserve energy.
28 June - Mir drifts out of control for hours after a computer problem disables the steering.
It is believed that a power surge or other electrical problem knocked out a computer as the crew slept. Meanwhile, Russian space chiefs plan to send Foale on a perilous spacewalk to execute repairs. But the plan is abandoned as problems mount on the ailing craft.
19 July - A rescue relief craft prepares to go to Mir to repair the ship. Mission control had previously entrusted repairs to the existing crew but decided a new team should undertake the work after the commander, Vasily Tsibliyev developed heart troubles.
5 August - Anatoly Solovyov and flight engineer Panel Vinogradov blast off in a Soyuz-U booster rocket to relieve Mir's beleaguered crew, who are facing new problems as their oxygen generators have broken down. The crew must now manage on their existing oxygen supplies and oxygen canisters.
Russian space officials play down the seriousness of the problem and stress that there is no immediate danger. It is only now revealed that the oxygen generators have been periodically breaking down throughout the past week.Reuse content