Cape Canaveral - For the first time in decades, Nasa plans to fly a spaceship during Christmas, giving up the holiday in order to revive the Hubble Space Telescope.
With Hubble out of action until astronauts deliver replacement parts, scientists and Nasa managers are rooting for a launch this week of space shuttle Discovery - even if it means working over Christmas.
Nasa has three chances to launch Discovery - Thursday, Friday or Saturday - before giving up for the year to avoid any potential Y2K problems.
Liftoff is set for 9:18 pm on Thursday (0218 GMT Friday). Good weather is forecast.
"My team and the shuttle team are willing to give up their holidays to do this," Hubble program manager John Campbell said on Wednesday.
Discovery's pilot, Scott Kelly, said: "I told my 5-year-old daughter that we're going to point the telescope at the North Pole and take a picture of Santa Claus, so she's really excited about that prospect."
In 38 years of human spaceflight, Nasa has flown only two missions over Christmas: Apollo 8 in 1968 and Skylab in 1973.
Men flew to the moon for the first time on Apollo 8, and Skylab was a space station with a permanent crew.
On Wednesday, as the countdown proceeded, engineers looked over documents and X-rays to make sure Discovery's external fuel tank is sound.
Nasa just learned that the wrong material was used to weld pressurization lines for a tank being built, and officials wanted to make sure the material was not used for Discovery's tank.
Late on Wednesday, after hours of analysis, Nasa declared Discovery's fuel tank safe to fly.
Besides the seven astronauts aboard Discovery, as many as 300 people will have to work over Christmas to support the flight, said shuttle program manager Ron Dittemore.
Dittemore said he has no idea how much that will cost in overtime pay.
"That's another one of those things that I haven't even worried about, because we're going to do it, and the cost is the cost and that's the way it is," he said.
As it is, Nasa is spending about R150 million a month to operate Hubble, whether it is working or not.
The telescope stopped working in mid-November when its system for pointing at stars failed.
Nasa never would have found itself in this predicament if Discovery had flown in October as planned.
The mission was put on hold, and the entire shuttle fleet grounded, after an exposed wire caused a short circuit during Columbia's launch in July.
A dented fuel pipe aboard Discovery further delayed the flight.
Dittemore said some managers have told him they have the sense that workers are disgruntled by the push to launch by year's end. But he said they are bothered by having their holiday plans spoiled, not because they feel rushed.
Dittemore said he expects more Christmas missions, what with the international space station under construction in orbit.
"It's not going to be uncommon in the future," he warned, "and so we better get used to that." - Sapa-AP