A NASA safety review released Wednesday found no evidence to support claims that astronauts were impaired by alcohol when they flew in space, NASA administrator Michael Griffin announced here at a news conference.

An independent external panel released a report late July including allegations that NASA astronauts drunk heavily before space flights.

Right after the report, NASA authorized chief of Safety and Mission Assurance Bryan O'Connor to conduct the monthlong review to evaluate the allegations. However, NASA said it found no evidence of improper use of alcohol by its astronauts.

O'Connor's review covered the past 20 years of NASA's space flight. He pored through records of shuttle, Russian Soyuz and other flights involving U.S. astronauts dating back to 1984. He interviewed astronauts, flight controllers, medical personnel and scores of other people who take part in training and evaluating crews and getting them ready to fly.

NASA's flight surgeons also said that they had no evidence of alcohol impairment by astronauts on flight day, nor any instance of their concerns to management being disregarded, according to O'Connor's 45-page report.

However, media reporters questioned the different conclusions from two investigations. O'Connor told the news conference that "the (external) committee chairman reminded me, as they had said when they first presented their report, that, admittedly, the alcohol allegation in their report was non-verified."

"They did not verify it. They heard this. They gave it to us to go verify, and so that's the ground rules we played by," added O'Connor.

NASA administrator said they take the July report very seriously. And in response to the report, NASA are moving forward on a number of actions and modifications of its policies, procedures and organizational structures that they believe will improve the astronaut health care systems.