The Russian Soyuz TMA-2 rocket, carrying Russian flight commander Yury Malenchenko and US flight engineer Edward Lu, lifted off at 0354 GMT and is due to dock with the orbiting platform early Monday.

All US space missions have been grounded since the Columbia shuttle disintegrated and burnt up on entry on February 1, killing all seven crew members and making Russia the only link with the 16-nation orbital station.

The Soyuz rocket tore up into the sky in a burst of orange giving off clouds of smoke.

Clapping erupted but Lu's brother Rick and fiancee Christine waited tensely as they watched the US cosmonaut on a TV screen as a countdown began toward orbit.

They looked anxiously on as the screen went fuzzy at one point and the image went off.

But nearly nine minutes into the flight, there were smiles of relief and loud clapping as it was announced that the craft had successfully reached orbit. "Oh, boy!" exclaimed Rick.

"It's ecstatic," said Christine. "I'm so relieved after that last stage. I was holding my breath. It's my first launch. The relief is overwhelming."

"We're so happy for him. He was so excited about the launch," said Rick. Lu's mother watched the lift-off from mission control in Moscow.

Some three hours into the flight, the crew prepared for the first engine-firing to correct their orbit and reported that all was fine onboard, NASA officials in Baikonur said after contact with Russian ground control.

Fred Gregory, deputy NASA administrator, who was present along with other top US and Russian space officials, including Russian Space Agency chief Yuri Koptev, paid tribute to the Russians.

"I was very impressed with the people, the professionalism and the successful launch. It's my first time on Baiknour," he said.

"It has been quite an achievement with the Russians and Americans, they have done a magnificent job," he said.

The United States and Russia are the biggest partners in the 16-nation ISS venture.

Since NASA grounded its remaining three space shuttles after the Columbia accident, Russia's Soyuz manned craft and Progress cargo vessels have been the only means to transport crew and supplies up to the ISS.

Russia has said it cannot raise the money to construct the additional manned Soyuz craft that are needed to service the platform and has appealed for international help, including the European Space Agency (ESA).

The United States says it cannot provide funding as the Iran Nonproliferation Act prohibits US funding for the Russian space program because of Moscow's nuclear and other military cooperation with Tehran.

Koptev, quoted by the ITAR-TASS news agency, said Saturday that he was to meet senior NASA officials in Moscow on May 5 to discuss possible further cooperation.

Because of the problem of getting supplies to the space station, which were mainly delivered by shuttles, future missions will comprise two, instead of three, astronauts.

Lu, 39, and Malenchenko, 41, will be eagerly awaited by the current ISS crew, US astronauts Kenneth Bowersox, Donald Pettit and Russian cosmonaut Nikolai Budarin, who were to return in March but had to extend their mission after the Columbia tragedy.

After a week to hand over control of the space station, the outgoing crew will make the journey back to Earth on May 4 in a Soyuz docked at the ISS. Lu and Malenchenko will be replaced by another two-man crew in October.

At the launch-pad in the barren Central Asian steppe, the two astronauts had climbed aboard the Soyuz craft some two-and-a-half hours before lift-off, hoisted to the hatch at the top on a hydraulic elevator.

The astronauts, wearing white space suits, underwent last-minute tests as Russian space technicians pressurized their suits to test them for leaks.

President Vladimir Putin telephoned a message to wish them well, officials said.

SPACE.WIRE