High crosswinds and low cloud in both Florida and California could keep the space shuttle Endeavour in orbit for another day.

Bad weather at both the Kennedy Space centre and Edwards Airforce Base are threatening to prevent the craft landing at the end of its week-long mission to map the Earth's surface using radar.

If Endeavour cannot land on any of its three tries later today, Nasa will attempt to land the shuttle at White Sands Missile Range, in New Mexico, on Wednesday. White Sands has been used for a shuttle landing only once before, 18 years ago.

The crew of six completed their mission on Monday. In just nine days and six hours they had surveyed three-quarters of the Earth's terrain, leaving out only the poles.

Finest portrait

When they come home, the astronauts will bring 300 digital tapes which will be used to paint the finest portrait of the Earth's face ever made.

All told, the radar aboard Endeavour mapped 112 million square kilometres (43.5 million square miles) at least twice. Scientists say that double imaging is needed to create precise 3-D maps of the Earth's topography as far north as Alaska and as far south as the tip of South America.

The United States Defence Department has said it will use the maps to improve its missile aiming and deployment of troops. Civilian users will have to settle for less precise data because of national security issues, but scientists say the information will still be far superior to what is currently available.

"There's every reason to be excited," said mission scientist Dr Thomas Hennig.

Fuel conservation

The astronauts would have mapped 6.5 million square kilometres (2.5 million square miles) more if a thruster had not malfunctioned on the end of the radar mast, the longest rigid structure ever flown in space.

A weeklong effort to conserve fuel aboard Endeavour allowed the astronauts to continue mapping on Sunday and bought an additional nine hours and 10 minutes for the mission.

When they land, the astronauts will have collected enough data to fill 20,600 compact discs. It will take scientists one to two years to go through it all.