The crew of the doomed shuttle Columbia was violently spun around in the cabin as the spacecraft desintegrated on reentry, 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 current fleet of three shuttles due to be retired in 2010.

After a highly detailed description of what happened to the seven astronauts when Columbia disintegrated as it reentered the atmosphere, NASA concluded that their safety belts, space suits and helmets failed to work as expected.

NASA deputy associate administrator Wayne Hale said the document was "the final report on Columbia."

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 of reentry and broke into pieces.

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, and "alternatives should be explored to strengthen the weak areas."

"The new suits that are going to be in Orion spacecraft under design right now would not have that problem, so the crew can be completely encapsulated at all the critical times," Hale said when the report was presented to the press.

It was not a problem with the Columbia crew, Hale 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 desintegrated.

The report also recommended that the parachutes shuttle crews wear during takeoff and descent should deploy automatically. Currently the parachutes deploy manually.

A chunk of insulation that broke off from the shuttle's external fuel tank during takeoff gouged Columbia's left wing heat shield, which led to the craft disintegrating as it re-entered the Earth's atmosphere on February 1, 2003.

NASA's fleet of three remaining shuttles was grounded for two years after the accident, while 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. The Challenger shuttle blew up 73 seconds after liftoff, killing seven astronauts on board on January 28, 1986.

The three 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.