"I think the flight does have extra meaning because of that, because of the fact that our close friends did perish just two months ago," Lu told reporters at a space training center outside Moscow.

"We of course will be thinking about them when we are up there, but that doesn't mean that we should stop what we are doing," he said. "If you stop at the first setback, you won't get anywhere."

Lu, 39, and Russian cosmonaut Yury Malenchenko, 41, are due to blast off for a six month mission on the International Space Station (ISS) on April 26 aboard a Russian-made Soyuz rocket.

They will fly on Sunday to the Baikonur cosmodrome in Kazakhstan, where the launch will take place.

After the US Columbia space shuttle disintegrated on February 1, killing all seven crew, NASA halted planned flights to the ISS and grounded the remaining three space shuttles.

Russia's spacecraft are now the only means of transporting crew and supplying the ISS, and Lu paid tribute to the Soviet-era program.

"The only reason we can continue this program right now is because the Russians have the capability to launch Soyuz and Progress spacecraft right now," he said. "That's very, very important.

"I do think that the international aspect of this is a very important part of the program, especially in the light of the situation in the world today," he said in reference to the war in Iraq.

"I think it's very important that we show the world what we can do together with our friends -- the Russians and the Europeans, the Canadians and the Japanese, and so on."

Kenneth Bowersox, Donald Pettit and Nikolai Budarin were due to return to earth in March, but their mission was extended following the uncertainty triggered by the Columbia disaster in which the seven astronauts aboard the US shuttle died as it disintegrated upon re-entry.

Moscow admitted for the first time this month that it would have to fund extra flights to the ISS following the US decision to ground its shuttle program.

The Russian government decided to earmark an additional 1.2 billion rubles (38 million dollars, 35 million euros) in budgetary funds to the space program over the next six months.

As long as Russia provides the transport, missions to the ISS will comprise two, instead of three, astronauts.

Jim Newman, NASAs chief representative in Russia, told reporters it would take at least a year before the United States could resume the shuttle flight programme.

"The question about when shuttle flights will be resumed is still unresolved. The investigation (into the Columbia disaster) is continuing.

"The optimists would say perhaps within a year, maybe a little less. It may be longer depending on the final conclusions," he said, adding that these should be ready by June.

The deputy director of the Star City astronaut training center, Andrei Maibarodi, said that despite the extra Russian government funding, Russia did not have the capacity to send more astronauts to the ISS.

"We are unlikely to increase production of transport craft, we can only expect more cargo craft to be produced," he said.

Russian cosmonaut Alexander Kaleri, who has trained along with US astronaut Michael Foale as a standby crew, said the space program would be affected by having just two cosmonauts on the orbiting space station.

"The need to cut the crew numbers means not all the tasks on the ISS can be carried out. Most of the work will be directed towards maintenance of the ISS, there is a big difference between two and three astronauts," he said.

SPACE.WIRE