I feel great joy that our Russian module is in orbit

Vladimir Lobachev, Moscow mission control

The Zvezda module - the "brain" and living quarters of the ISS - lifted off on a Proton-K rocket at 0456 GMT.

The rocket could be seen soaring into a clear blue sky, trailing a cone of flame.

The Proton's three stages fell away, one at a time, as planned, and within nine minutes of blast-off, the rocket had entered orbit.

American William Shepherd will lead the first crew in October

Zvezda's solar panels and several antennae were reported to have unfolded shortly after deployment.

Russian and US space agency officials, who had been monitoring the launch on a giant screen at mission control in Moscow, gave loud applause when they knew everything had gone well.

"I feel great joy that our Russian module is in orbit but we still have some worries," said Vladimir Lobachev, director of mission control. "If the docking goes successfully, then we'll celebrate."

Robert Castle Jr, Nasa's flight director for shuttle and station mission operations, described the mood among Russian and US officials as "ecstatic". "It's a major step in both countries' space programs," he said.

Pizza sponsorship

The Russian-built module will orbit the Earth for two weeks before linking up with the embryonic ISS 400 km (250 miles) above the planet's surface.

If Zvezda fails to dock successfully then it is understood a three-man team, known as the "zero crew", currently on standby at Baikonur, will race into space and make the connection manually.

Zvezda has gone up nearly two years behind schedule - a delay that is thought to have cost the multinational space station project as much as $3bn.

Zvezda (left) will link with Zarya and Unity on 26 July

Zvezda module

Length (end-to-end) - 13 metres Gross launching weight - 19 tonnes Launch vehicle - 3-stage Proton rocket Launch site - Baikonur cosmodrome, Kazakhstan Inclination of orbit - 51.6 degrees Orbit at rendezvous - 386 km Wingspan - 30 metres Pressurised compartments - three Windows - 13 Rendezvous - 0110 GMT on 26 July

The first long-stay ISS crew should arrive at the end of October.

The new module will make their lives as comfortable as is possible in the micro-gravity of Earth's orbit.

Zvezda, which means "star" in Russian, will provide air, water, cooling and food for the astronauts, additional electricity for experiments, and a docking port for vehicles coming to and from the station.

Zvezda's main compartment consists of a laboratory, three sleeping areas, a bathroom, galley and exercise facilities. Its 13 windows will provide one of the best views in history.

The ISS currently comprises two modules: the US-built Unity and the Russian module Zarya.

The ISS, a joint venture involving the United States, Russia, Europe, Japan and Canada, is expected to cost $60bn when completed, perhaps by 2005. The first ISS crew is expected to take up station in October under the command of US astronaut William Shepherd.