By Alan Quartly BBC, Moscow

Malenchenko and Lu are due to blast off next week

A joint Russian-US space crew has begun final preparations for the first flight to the International Space station (ISS) since the Columbia space shuttle disaster.

US space agency (Nasa) astronaut Ed Lu and Russian cosmonaut Yury Malenchenko are completing training at Star City, Russia's cosmonaut training centre, in a mock-up of a Russian Soyuz spacecraft - now the only way for people to fly to the ISS.

The two men - an experienced crew who carried out a gruelling spacewalk outside the ISS together in 2000 - are due to blast off from Russia's launch site in Kazakhstan on Saturday.

Obviously the first few weeks were difficult - after the loss of our friends we had many other things to think about Ed Lu

After Columbia disintegrated upon re-entry on 1 February, killing all seven crew on board, Malenchenko and Lu were forced to modify their training programme.

For the past two months, they have undergone intensive training in the use of the Soyuz craft, which Russia has operated since the mid 1980s to carry its cosmonauts into space.

'All business'

Officials at Star City admit the Columbia disaster forced them to cram the Soyuz training into a much shorter period of time than normally allocated.

Another Soyuz craft is permanently docked to the space station. In the absence of Nasa shuttle flights, it is the only way down for the current ISS crew of two Americans and one Russian.

The current crew will return in the Soyuz

Lu and Malenchenko have been spending up to 12 hours per day in the Soyuz simulator at Star City.

Lu, 39, a physics PhD, admitted things hadn't been easy: "Obviously the first few weeks were difficult. After the loss of our friends we had many other things to think about. But once you get down to work, it's all business because we have a job to do. I think we're ready."

Reduced scope

With the resumption of space shuttle flights on hold until Nasa investigators find out what caused the Columbia crash, crew numbers will be reduced from the usual three to two to save station resources.

The Soyuz is the only way of reaching the ISS

"I think there will be more work than we normally have," said Lu. "I think it will make it more of a challenge."

Malenchenko, 41, a Russian air force colonel, has flown on American shuttles and the Russian Mir space station.

The absence of shuttle flights, he said, meant the crew had had to reduce the scope of the scientific programme planned for the mission.

Income loss

But with the world's attention now focused on the Russian side of the ISS programme, it has become apparent that Moscow desperately needs more funding to deal with the increased burden it now bears.

Although the Russian Government has pledged an extra $38m, officials privately concede this may not be enough to finance the construction of the extra Soyuz and Progress cargo ships now required.

The Russians are also deprived of much needed income derived from the "space tourist" programme; the Columbia disaster has forced its suspension.

So far two businessmen have paid up to $20m for spaceflights.