Space shuttles still pose a risk

Earlier this month John Muratore, author of one of the documents acknowledged that even marshmallow-size pieces of insulating foam from the fuel tank could doom the space shuttle under the worst circumstances. He told reporters it is a risk NASA and the United States must accept for flights to resume anytime soon, and that it would take a total re-design of the tank to completely eliminate foam loss.

To achieve a profound safety improvement, he said, NASA would need to replace the shuttle fleet, which was designed in the 1970s, with an entirely new vehicle.

NASA officials said that the Discovery shuttle, due for lift-off on 22 May is safer than it has ever been because of changes made after the Columbia disaster, and they have long acknowledged that not all debris risk can be eliminated.

Emma Browne