The first concerned the carbon-carbon reinforced thermal insulation tiles which protect the vessel, including the leading edges of its wings, from ferocious heat during re-entry to Earth's atmosphere.

The Columbia Accident Investigation Board (CAIB) found that the current inspection regime was inadequate and recommended a more comprehensive plan to check the structural integrity of the insulation be put in place before the resumption of any shuttle flights.

The Board also called on NASA to reach agreement with the US military's National Imagery and Mapping Agency (NIMA) to make in-orbit imaging for each shuttle flight standard requirement.

"This recommendation was issued because of the board's finding that the full capabilities of the United States government to image the shuttle on orbit were not utilised," the CAIB said in a statement.

Two and a half months after Columbia disintigrated on re-entry to Earth's atmosphere, killing all seven astronauts on board just 16 minutes prior to scheduled touchdown, investigators are still looking for a definitive conclusion as to the cause of the tragedy.

They are focussing on apparent excessive heating of the left wing during re-entry, which may have come about after the heat-resistant tiles were damaged by pieces of insulating foam flying off the external fuel tank just 81 seconds after lift-off.

SPACE.WIRE