Nasa officials have again delayed the launch of space shuttle Atlantis after a sensor on a fuel tank appeared not to be working.
The US space agency Nasa has delayed launch of the Atlantis shuttle until 2008 because of a persistent problem with a sensor on a fuel tank.
Lift-off had been scheduled for 1521 local time (2021 GMT) on Sunday, three days later than originally planned.
Two attempts to launch the shuttle have been cancelled since Thursday, and only a few days remained for launch in the current window.
But a Nasa spokesman said the latest launch attempt had been cancelled, and no new time has been announced.
The 11-day mission was due to deliver Europe's first permanent space lab to the International Space Station (ISS).
The 11-day mission is due to deliver Europe's first permanent space lab to the International Space Station (ISS).
A preliminary launch date has now been set for 2 January.
The fuel sensors are part of a critical system which cuts off the shuttle's main engines if the fuel tank runs dry, for example because of a leak or technical problem.
Failure to do so could cause a fire or explosion.
End in sight
The current launch window for the shuttle lasts until Thursday, after which conditions will not be right for the mission until January.
The main task of the mission is the delivery and installation of the European Space Agency's (Esa) Columbus space laboratory to the ISS.
The 21-tonne, 880m euro ($1.3bn) module is designed to carry out experiments that would be impossible in the gravity experienced at the Earth's surface.
The eventual arrival of the European space lab at the ISS will mark the end of a 12-year effort for Europe to establish its first permanent base in space.
The project has already been hit by several hold-ups in space station construction, which resulted in its costs rising.
The first occurred between 1996 and 2000, as a result of Russian delays launching the ISS's main control and habitation module, Zvezda.
Further delay resulted from the destruction of space shuttle Columbia in 2003, which claimed the lives of seven astronauts.
The US space agency spent three-and-a-half years and more than $1bn fixing the shuttle for a return to flight in 2005.
However, the shuttle fleet was swiftly grounded again after the same problem responsible for dooming Columbia - foam shedding from the external fuel tank - re-emerged on the 2005 mission.
Columbus will be the second laboratory to be added to the space station. It will join Nasa's Destiny module, which became operational in 2001.
The third and final lab, Japan's Kibo, will be taken up to the ISS next year. However, because of its size, it will require three shuttle missions to deliver all of the Japanese components.
The 11-day mission will involve at least three spacewalks, deliver a new crew member to the ISS, and bring back an astronaut who has completed a two-month stay on the space station.
