"I was unable to verify any case in which an astronaut spaceflight crew member was impaired on launch day, or any case where a manager of a flight surgeon or co-crew member disregarded their recommendation that a crew member not fly," wrote Bryan O'Connor, NASA's chief of safety and mission assurance, in the report. "I am confident that there are reasonable safeguards in place to prevent an impaired crew member from boarding a spacecraft."
The allegations surfaced in a July report by the Astronaut Health Care Review Committee. The committee was established in February after the high-profile arrest of astronaut Lisa Nowak in an alleged attack on a romantic rival. The members were tasked with evaluating the medical and mental health services available to astronauts at the Johnson Space Center in Houston.
"Two specific incidents were described where astronauts had been so intoxicated prior to flight that flight surgeons and/or fellow astronauts raised concerns to local on-scene leadership regarding flight safety," the report noted. "However, the individuals were still permitted to fly."
NASA officials immediately questioned the allegations of astronaut drinking.
Astronaut Scott Kelly, who led a shuttle mission this month, wrote a letter to several newspapers saying any suggestion that "my crew or I would ever consider launching on our mission in anything but the best possible condition is utterly ridiculous."
The Wednesday report supported Kelly's general assessment, but issued five recommendations aimed at clarifying the role of flight surgeons in determining whether astronauts were impaired and reiterating the agency's alcohol policy. Those recommendations included stationing flight surgeons in the rooms where astronauts suit up before missions, adding "drinking to excess" to a list of high-risk behaviors and considering whether to make alcohol testing mandatory.
NASA Administrator Michael Griffin noted O'Connor's report surveyed 20 years of flight records, and said, "His review found no evidence that astronauts were ever impaired by alcohol."
But Griffin also emphasized that the agency is developing an astronaut code of conduct to codify long-standing expectations of behavior.
O'Connor said the investigation was unusually comprehensive, noting that since 1972, the only investigations for which he had spoken to more witnesses were the probes into the Columbia and Challenger disasters.
"We take these allegations very seriously," Griffin said, "but I've also said that the stories cited seem improbable."