The investigative team's final report included 30 recommendations to improve spacecraft design and crew safety, NASA said in a release. The recommendations cover a number of subjects from crew training, restraints and individual safety equipment to spacecraft design methods to future accident investigations.
The report found the astronauts knew for about 40 seconds that they did not have control of the shuttle before they likely were knocked unconscious as Columbia broke apart, CNN reported.
"(The) breakup of the crew module ... was not survivable by any currently existing capability," the report said.
Also, the report found that while crew members were wearing their pressurized suits, one astronaut did not have on a helmet, three were not wearing gloves and none lowered the visors before the module lost cabin pressure. One astronaut also was not seated.
NASA said it already implemented some of the recommendations and is evaluating others.
The investigation was conducted by a multidisciplinary NASA team based at NASA's Johnson Space Center in Houston. The study team also consulted experts outside of NASA for portions of its work.
"The members of this team have done an outstanding job under difficult and personal circumstances," Johnson Space Center Director Michael Coats said. "Their work will ensure that the legacy of Columbia and her heroic crew continues to be the improved safety of future human spaceflights worldwide."