The crew of the doomed shuttle Columbia was violently spun around in the cabin as the spacecraft disintegrated on re-entry, NASA says in its final report on the 2003 tragedy that includes safety recommendations.
The 400-page report took four years to complete and its conclusions will be used in configuring the future Orion spacecraft that will eventually replace the US space agency's current fleet of three shuttles due to be retired in 2010.
In a highly detailed description of Columbia's final moments, the report on Tuesday said the seven astronauts were unaware their re-entry was compromised. The pilot tried to take control of the shuttle ignoring that his efforts would be in vain, as Columbia exploded over Texas on February 1, 2003.
Things happened so fast that none of the crew, including an Israeli astronaut, were able to close the visor of their helmets - one astronaut was not even wearing one, the report said.
"Pilot in seat 2 takes action in apparent attempt to restart auxiliary power unit (APU) 2 and 3. With the loss of hydraulic pressure ... These actions took place ... after GMT 14:00:05 ... and prior to loss of consciousness," it added.
"There were a number of alarms going off simultaneously. The crew was trying very hard to regain control. We're talking about a brief time in a crisis situation," NASA deputy associate administrator Wayne Hale said on a media conference call.
Columbia blew apart some 20,000 metres above the Earth as it was returning from a 16-day space mission to land in Florida.
A chunk of insulation that broke off from the shuttle's external fuel tank during takeoff gouged Columbia's left wing heat shield, allowing superheated gases to melt the shuttle's internal structure, leading to its explosion.
In the report, investigators admitted they could not clearly determine whether the astronauts were dead or unconscious due to the sudden decompression of the cabin just before the shuttle lost control upon re-entry.
The report said "the seat inertial reel mechanisms on the crews' shoulder harnesses did not lock.... As a result, the unconscious or deceased crew was exposed to cyclical rotational motion while restrained only at the lower body.
"Crew helmets do not conform to the head. Consequently, lethal trauma occurred to the unconscious or deceased crew due to the lack of upper body support and restraint."
"Crew survival suits should be evaluated as an integrated system to determine the various weak points - thermal, pressure, windblast, chemical exposure," the report recommended.
"Alternatives should be explored to strengthen the weak areas."
Hale said the new suits that will be used in Orion spacecraft "would not have that problem, so the crew can be completely encapsulated at all the critical times."
It was not a problem with the Columbia crew, he said, adding: "it is a basic problem of suit design ... and that we intend to fix in the future."
The Orion is a component of Constellation, a National Aeronautics and Space Administration program that includes new launch vehicles for future missions to the moon and Mars. It is scheduled to replace the shuttle fleet in 2014.
Hale said the integrated system recommended in the report would not have saved the Columbia crew from its fate, since the entire shuttle disintegrated.
The report also recommended that the parachutes shuttle crews wear during takeoff and descent should deploy automatically. Currently the parachutes deploy manually.
NASA's fleet of three remaining shuttles was grounded for two years after the Columbia disaster. The shuttle's safety features were improved and rigorous inspection procedures of the thermal shield when the shuttle is airborne were adopted.
The Columbia tragedy was the second shuttle accident since the program was launched in 1981. On January 28, 1986 the Challenger shuttle blew up 73 seconds after liftoff, killing seven astronauts on board.
The remaining shuttles - Discovery, Atlantis and Endeavour - are due to make eight more flights to the orbiting International Space Station to finish construction and carry out the last maintenance mission on the Hubble Space Telescope.
The fleet is due to be decommissioned in 2010, after 30 years of service.