Europe's orbital outpost

Two attempts to launch the shuttle have been cancelled since Thursday, and only a few days remained for launch in the current window.

The 11-day mission was 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.

Three of the sensors failed during a launch attempt on Thursday, while at an attempt on Sunday only one malfunctioned.

"This could all be good news because it may give us some data points that we did not have as to what may be behind this problem," said Nasa spokesman George Diller, quoted by the Associated Press news agency.

Permanent base

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 12.8-tonne, 1.3bn euro ($1.8bn; �0.9bn) 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.

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.