The April 22 internal report from the team led by NASA flight director LeRoy Cain examined three options to reduce the shuttle's weight by as much as 16 tonnes, and concluded none would have reduced the extreme heat of re-entry enough to save the doomed spacecraft.

The report also noted the extreme risk of shedding unnecessary equipment, such as scientific experiments, and said it would only be justified by "significant and convincing data" proving the shuttle would not survive re-entry.

Columbia broke up February 1, killing all seven astronauts on board, just 16 minutes prior to its scheduled touchdown.

Investigators believe heat-resistant tiles on the shuttle's left wing were damaged at liftoff by pieces of insulating foam flying off the shuttle's external fuel tank, allowing superheated gases to enter and burn up the spacecraft.

Two weeks ago, an independent board investigating the loss of the Columbia recommended a comprehensive prelaunch inspection of each shuttle's heat shield.

The board also called on the US space agency to enlist the US military's satellites to photograph each shuttle flight in orbit.

SPACE.WIRE