By Irene Klotz
Cape Canaveral, Florida
When astronaut Thomas Reiter climbed aboard shuttle Discovery on Thursday for a practice launch countdown, it was as close as he has ever come to flying on a US spaceship.
Thomas Reiter is no stranger to long-duration spaceflight
But unlike half the US space agency (Nasa) astronauts assigned to Discovery's upcoming mission, Reiter is no rookie flier.
The German-born astronaut spent six months in orbit on Russia's Mir space station.
Now, after nearly a decade, Reiter, 48, is preparing for a second long-term stay in space, this time aboard the International Space Station (ISS).
The European Space Agency (Esa), which paid Russia for a crew slot, is counting on Reiter's flight to jump-start its stalled microgravity and life sciences programmes.
"We have been waiting for quite some time," Reiter said in an interview.
Europe's primary contribution to the space station, the Columbus laboratory module, arrived at the Florida launch site two weeks ago, joining a long queue of space station components awaiting shuttle rides to orbit.
Space station assembly has been on hold since the 2003 Columbia accident.
Nasa grounded the shuttle fleet for safety upgrades and flew an initial test-flight last July.
Problems with the shuttle's fuel tank, which triggered Columbia's demise, reappeared during Discovery's lift-off last year.
With flights on hold, costs to maintain the Columbus engineering team and research community spiralled.
The Esa had spent between $6bn and $7bn designing and building the module, and another $500m a year for operations, said Alan Thirkettle, Esa's International Space Station Programme Manager.
"The delays have imposed some difficulties," Reiter explained.
"The main goal was to keep these people together. That was quite a challenge - we are all desperately waiting for the moment when Columbus will be docked to the station. "
Back to three
Nasa hopes to launch Columbus next year, but the shuttle's flight schedule hinges on Discovery's upcoming mission.
Managers plan to set a launch date for Discovery on Saturday following a two-day flight review. The target date is 1 July.
"It's still not clear when assembly will resume. We're trying to use this time to foster the public consciousness," said Reiter, who will become the first live-aboard station crewmember who is not from the United States or Russia.
The Discovery orbiter is aiming for a July launch window
Reiter will join cosmonaut Pavel Vinogradov and astronaut Jeffrey Williams, who have been living aboard the station since April.
With Reiter's arrival, the station returns to a three-member crew for the first time since the Columbia accident.
The crew was cut to two to save on supplies while the shuttle fleet was grounded.
"All of the agencies that are involved in the programme are looking forward to the moment when we really can utilise the station for its originally designed purpose: to act as a multi-functional research laboratory," Reiter said.