One giant leap, three astronauts and two days to turn a page in space history

Some time tomorrow, Bill Shepherd, Yuri Gidzenko and Sergei Krikalev will swing open a hatch 240 miles above the Earth and begin a race against time. As the first people to live on the International Space Station, a work-in-progress whirling around the Earth, they have the responsibility of getting it operational before the air they have taken with them runs out - in about two days.

Some time tomorrow, Bill Shepherd, Yuri Gidzenko and Sergei Krikalev will swing open a hatch 240 miles above the Earth and begin a race against time. As the first people to live on the International Space Station, a work-in-progress whirling around the Earth, they have the responsibility of getting it operational before the air they have taken with them runs out - in about two days.

It is a genuine drama, the first that has actually mattered on the space station in an already long history (although the first components were only launched two years ago).

For the trio of astronauts - an American and two Russians - the deadlines will be very real. Although virtually everything they need is already on board the structure, having beendelivered by supply flights since the living quarters were added in July, it will need Shepherd's expertise to create a habitable space. The first tasks will be just like arriving in any home: turn on the lights, the heating and air controls, take a look at the toilet and bedrooms (actually just bunks), start a meal, make a phone call - or more precisely, get in touch with Mission Control (a responsibility shared between the Baikonur Cosmodrome in central Asia, and the Johnson Space Centre in Houston).

If it goes wrong though, and the station refuses to start up, they will have to scramble for the lifeboats, and return to Earth - which will put yet another delay into a project which has suffered repeated setbacks since it was first suggested by Ronald Reagan in 1984.

Assuming the astronauts are successful in starting the station, their four-month mission will herald a new era in space travel: there will be someone continuously on board on the space station for at least 20 more years. "If all goes well on this and future missions," said the US space agency Nasa, even more optimistically, "then October 30, 2000, will go down as the last day on which there were no human beings in space."

The Mir space station, launched in 1986, was occupied for most of its life - though it was left empty for brief periods during its operational life, and was empty from August 1999 until April this year, when a relief crew went up to investigate what needed to be repaired.

Mir's longevity grew out of Russia's inability to conceive of giving up its place in space, especially once the Americans brought down their own Skylab space station when it reached the end of its life.

When Shepherd swings open the hatch 90 minutes after arrival tomorrow, it will begin a new era in which humans will assert their occupation of space. Shepherd, known for his expertise in getting systems working, had been training for the flight for five years. He blew kisses to his wife before he left and kept flashing a thumbs-up to his colleagues, and shouted "Let's go do it!" before he climbed into the Soyuz rocket, only the second American to launch in a Russian rocket.

There was no Nasa-style countdown at the cosmodrome, only occasional and curt reports blaring from loudspeakers. Several seconds before liftoff, the command, "Zazhiganiye" (Ignition) was given and the 20 engines burst into flames. Clouds of dark smoke rolled across the desert. The huge rocket whizzed into the air - departing from the same place that had seen other milestones in the human exploration of space, including the launch of Sputnik in 1957 and Yuri Gagarin, the first person in space, in 1961.

The Nasa administrator, Dan Goldin, waited until Shepherd and his crew were safely in orbit before hugging top Russian officials and giving a high-five to Joe Rothenberg, his deputy. The deputy director general of the Russian Space Agency, Valery Alaverdov, pressed a goblet into Goldin's hands and poured scotch from a bottle. "Success," Alaverdov toasted. "Here's to a great space programme," Goldin replied.

A great one, or a late one? The International Space Station (ISS) has been delayed and delayed. When the first parts of the ISS blasted into space, they were already two years late. Russia has delayed providing its parts because of budget cuts and through the stubborn streak among some of its planners, who even now want to keep Mir in operation.

Every time you look, the ISS schedule has slipped again, and its budget has ballooned. In November 1998, the expected completion date was 2003, and the budget around $50bn. Now it is 2006, and nobody is talking about the costs.

Once built, the ISS will be the size of a three-bedroom house, with solar cells covering the area of two football fields. Indeed, one of the first supply missions will bring up more solar cells to provide power for the growing needs of the astronauts.

Goldin has seen Nasa's existence threatened by cutbacks, but fought back through instituting a credo of "better, faster, cheaper". Even as the rocket with Shepherd and his Russian colleagues sped upwards, he was defending the ISS: "There are so many people who felt maybe we couldn't do it. But it's happening," he said. "We're going to be in space forever with people who are circling this globe and then we're going on to Mars, back to the Moon and with bases on asteroids."

One of the first questions people ask about the ISS is what are they going to do there? Michael Foale, the British-born astronaut who was on board Mir when it was holed by a cargo ship, and is now in charge for Nasa of the space station crews, said: "This flight is the keystone for all future explorations from this planet."

Initially, however, it will be a laboratory for microgravity experiments which would be hard (though not impossible) to carry out on Earth. Critics say it would be just as cost-effective to do the latter and it would not entail living in an environment where a stray piece of space junk could destroy everything.

But that is just the worst that could happen. In all likelihood, the ISS will continue whizzing overhead, visible at night as a bright, moving light, which children will be able to recognise as our colony in space.