Columbia's last mission ended in disaster

A senior official, Bill Readdy, said any decision would depend on the results of the investigation into the break-up of the shuttle Columbia as it re-entered the Earth's atmosphere on 1 February.

Engineers have been put on standby to fix problems already raised by the investigating board, and devise a way of checking the exterior of the shuttle for defects while it is in orbit.

Mr Readdy also explained why he turned down an offer from the Defense Department to take satellite pictures of the damaged Columbia while it was in space.

He said the shuttle was not believed to be in any danger at that point and it was expected to be able to land safely.

Stand-by

In an internal memo, Mr Readdy, Nasa's deputy administrator, wrote: "The team will prepare for a safe return to flight as soon as practicable.

"As a goal, the SSP [Space Shuttle Programme] shall plan for corrective actions and reviews which support a launch opportunity as early as the fall of 2003."

Such actions include modifications surrounding the insulating foam, part of which broke off and struck Columbia on lift-off.

It is suspected of having damaged the shuttle's protective tiles, causing the craft to overheat on re-entry.

Mr Readdy also asked his team to devise a system of checks to be able to identify problems with a shuttle while it is still in orbit.

"That's the elephant in the room. We don't want to ignore those [issues]," he said.

Phased out?

Mr Readdy said Nasa would be guided by the findings of the Columbia Accident Investigation Board, which is exploring what caused the disaster.

The agency would not "prejudge" the outcome of the investigation, he said.

Nasa's chief administrator Sean O'Keefe said it was possible but unlikely the remaining three shuttles will not return to space.