Edward Lu and Russian cosmonaut Yury Malenchenko will head Saturday from the Baikonur Cosmodrome in Kazakhstan for a six-month mission on the International Space Station (ISS).

Two days ahead of the launch, the 57-metre (188-foot)-long Soyuz vessel slowly rolled out of its hangar, a locomotive pushing it along a railway track 1.2 kilometres (0.7 miles) to the launch site.

The orange and grey craft, which has a white capsule at its tip for the crew, will be hoisted upright and then undergo final safety checks as the countdown begins to the historic mission.

Lu, a 39-year-old Chinese-American who has been on two previous space flights, spent two months training at the Star City astronaut centre outside Moscow before arriving at the isolated semi-desert region of Kazakhstan last Sunday.

The rocket -- the 415th manned one from the Soviet-era launchpad -- will blast off at 0354 GMT Saturday and the crew will dock at the ISS 48 hours later.

Lu's younger brother, Rick, 33, who will witness the launch together with Edward's fiancee and several top NASA officials, said the US astronaut was looking forward to the spaceflight.

"There's not much of any fear. My brother is excited to be part of this mission. There is of course risk, but Ed accepts that risk is part of the job," he told AFP.

The current ISS crew, US astronauts Kenneth Bowersox, Donald Pettit and Russian cosmonaut Nikolai Budarin, who heard in horror about the fiery death of their colleagues on the shuttle, are themselves soon to make the journey back to Earth.

After a week to hand over control of the space station, the outgoing crew will re-enter the atmosphere on May 4 in a Soyuz craft currently docked to the ISS, landing in Kazakhstan to complete their five-month-plus mission.

NASA grounded the remaining three space shuttles after the February 1 accident and has had had to turn to cash-strapped Russia to transport crew and supplies to and from the orbiting space station.

Although Russian Soyuz technology is more than 35 years old, the craft has an excellent safety record, with only two crashes involving Soyuz manned space missions.

"It's the most reliable spacecraft in the world in terms of its safety record. They've been flying Soyuz vehicles for 36 years but they've only had two accidents," NASA spokesman Rob Navias said.

Denied financial assistance from Washington for its space program under US law because of Russian military cooperation with Iran, Moscow has budgeted an additional 1.2 billion rubles (38 million dollars, 35 million euros) over the next six months.

But thinly-stretched resources mean that to cut down on spending, future missions to the ISS will comprise two, instead of three, astronauts.

This will largely limit the next crew's activities to maintenance of the space station, meaning that no more spacewalks are likely to take place this year.

After the Columbia disaster, Moscow took on an obligation to fly two manned Soyuz flights and five unmanned Progress cargo craft to the ISS this year. Water and food supplies were mainly delivered by US shuttles.

Forty astronauts were to have visited the ISS in 2003 onboard two Russian Soyuz rockets and five US shuttles while three Russian Progress cargo craft were to deliver supplies and nudge the station into a higher orbit.

SPACE.WIRE