Tonight's not our night

Steve Altemus Nasa test director

Endeavour is scheduled to carry seven astronauts to the International Space Station (ISS), including the new resident crew.

Two of the astronauts are last-minute replacements for crew members who had to be pulled off the mission on medical grounds - the first time Nasa has had to switch crews since the fateful Apollo 13 voyage.

The 16th shuttle mission to the ISS was to have lifted off at 0059 (0559 GMT) on Monday, but with three hours to go the launch was cancelled.

Oxygen leak

The problem was a leak in the system that provides oxygen to the crew's helmets.

"Tonight's not our night," said Nasa test director Steve Altemus.

"I think you guys'll want a healthy vehicle before we cut you loose," he told the crew.

The shuttle had already been loaded with more than 1.9 million litres (500,000 gallons) of rocket fuel.

The launch will now take place on 18 November at the earliest.

Crew replacements

Top of the mission agenda is the assembly of a huge beam on the ISS using the station's robotic arm, which will form part of the cooling system.

The beam will increase the length of the main section of the ISS by 14 metres.

Two of the original mission crew, Donald Thomas and Endeavour pilot Christopher "Gus" Loria, were replaced in the summer after both suffered medical problems.

Pilot Paul Lockhart is a last-minute replacement

Taking their seats are shuttle pilot Paul Lockhart and Donald Pettit, who along with Commander Ken Bowersox and Flight Engineer Nikolai Budarin will make up the sixth resident crew on the ISS.

The station's current crew will return to Earth on the shuttle after more than five months on board.

Nasa's experts had debated for months whether to ground Thomas for an undisclosed medical condition.

"It was one of those things that was right on the line," said expedition commander Kenneth Bowersox.

"I had trouble sleeping before it happened because I was so worried about which way we should go and what was right and what was wrong and the best way to handle it," he added.

Just a couple of weeks later the pilot Loria injured his back at home, forcing him out of the mission too.

The change sent shock waves through the crew - not since the ill-fated voyage of Apollo 13 has a career astronaut been removed from a mission.

There were also technical problems as Nasa had already delivered the food and clothes Thomas would use during his stay on the ISS, leaving Petit with wrong provisions and clothes that are too small.

To cope he has stashed some of his favourite food and some bigger shoes and trousers on the shuttle.

Superstition

The other problem is one of superstition as the flight number for the mission is STS 113 - uncomfortably close to the unlucky 13.

The Kazakh landing was reportedly difficult

"We were joking a lot about being Number 113," explained Bowersox, who said they had pondered changing the mission's number.

Playing it safe, the astronaut's mission patch reads in Roman numerals - CXIII.

On Sunday morning at 0604 (0004 GMT), two Russian cosmonauts and a Belgian astronaut landed in Kazakhstan after a 10-day stint on the ISS.

The landing was reported to have been a little difficult. "The landing was a little hard, maybe because it was dark," said flight commander Sergei Zalyotin.

But all of the crew were reported to be fine.