NASA has postponed Thursday's scheduled launch of space shuttle Atlantis after discovering a problem with a sensor in the shuttle's fuel tank.
Atlantis was set for an afternoon launch in Florida, carrying a crew of seven and Columbus -- a European science lab.
The cancellation came after two of the four sensors in the shuttle's liquid hydrogen tank showed the tank was empty, even though there was fuel inside.
NASA spokesman Paul Foerman said at least three sensors must be functioning properly before a launch could go ahead.
The sensors are necessary for ensuring that the shuttle's three main engines don't shut off too early or too late during liftoff.
According to shuttle managers, the next launch attempt would be no earlier than Saturday.
"We want to sleep on it," said LeRoy Cain, chairman of the mission management team. "We want to encourage the engineers and the rest of the team to sleep on it and think about what we might not be thinking about yet."
Columbus lab
Columbus would be the second scientific laboratory to be added to the International Space Station, following the Destiny lab brought up in 2001.
Before the announcement of the delay, Col. James M. Kelly, a NASA astronaut, said the primary purpose of the mission is to double the laboratory space on the international side of the space station.
"We are getting ready for a bigger crew of six people that will happen later on next year, this is going to give us a whole lot more space," Kelly told CTV's Canada AM on Thursday.
"There's going to be a lot more internal space for them to live and work in."
Columbus, at a cost of $2 billion, was built by about 750 Europeans over nearly a quarter-century.
Japan's huge lab, Kibo, will be sent up to the ISS in three sections starting in February.
Inside Columbus, scientific work will start almost immediately once it is attached to the ISS.
NASA is under presidential orders to complete the ISS and retire its three remaining shuttles by 2010.
"We're already working on its successor, the CEV (Crew Exploration Vehicle) project, which we hope to launch in the 2015 timeframe," said Kelly.
He said the goal then will be to "head ourselves back to the moon and onto Mars."
After the next Atlantic launch, NASA will have to complete 12 shuttle missions to the ISS to meet the 2010 deadline. One other mission is planned to the Hubble Space Telescope next summer.
In 2003, a damaged heat shield caused the Columbia disaster. Foam broke free of the shuttle's external tank during liftoff, cutting into a wing. When the shuttle returned to earth, superheated gasses passed through the opening, destroying Columbia and killing all seven astronauts.
With files from The Associated Press
