The impact of falling foam during the space shuttle Columbia's launch was confirmed as the physical cause of the disaster by the final report of the Columbia Accident Investigation Board. Also confirmed were the specific technical changes that NASA must implement before the shuttle fleet can fly again.
The new aspects of the CAIB report, released in Washington DC on Monday, were sharp criticisms of the way NASA manages its operations. "NASA's organizational culture had as much to do with this accident as foam did," the report says.
But the publication of the report brings to an end a seven-month investigation that examined 30,000 documents and emails and conducted 200 formal interviews. On the physical cause of the accident, the report sets out the following chain of events.
During the launch of Columbia, a piece of foam fell from an external fuel tank and crashed into heat-resistant tiles on the leading edge of its left wing. Tests conducted by CAIB in which pieces of foam were fired at a spare wing demonstrated that such impacts could cause fatal damage.
The resulting hole allowed superheated gas to get inside the wing during re-entry 16 days later on 1 February. The gas melted the aluminium frame, quickly leading to complete disintegration and the loss of all seven crew.
A sudden increase in temperature inside the left wing was reported in telemetry transmitted from Columbia in its final moments and data retrieved from an in-flight recorder recovered from debris. Some NASA engineers concluded the damage sustained during take off did not pose a risk to Columbia because similar foam damage had been seen on previous launches.
Before shuttles flights can resume, NASA will have to comply with CAIB's recommendations. These include preventing the loss of foam from the shuttle's external fuel tank, improving the high-resolution imaging of shuttles during launch and in orbit to check for problems, and implementing the ability to make repairs to the shuttle's heat shield in orbit.
These are the "before return to flight" recommendations. But the changes required to resolve the management failings so heavily criticised by the CAIB report are described as "continuing to fly" recommendations. These could include an independent safety assurance organization.
One point made by the CAIB report that NASA will agree with is that space shuttles should "return to flight at the earliest date consistent with the overriding objective of safety". NASA has a "planning target" of March or April 2004.
The shuttle fleet is crucial to the continued construction and operation of the International Space Station. It is currently only possible to reach the outpost using much smaller Russian Soyuz spacecraft. This has meant suspending construction work and limiting the station's crew to just two.
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