(CNN) -- There's been only one incident of a NASA crew member being impaired by drugs or alcohol close to a launch, but never on a launch day, according to a new survey of active-duty astronauts and flight surgeons.
NASA has called reports of astronauts who were drinking or hung over on launch day an "urban myth."
The person was seen to be impaired in the time leading up to the launch because of an apparent interaction between prescription medication and alcohol.
"Medical personnel in performing their routine preflight monitoring assessed the situation and determined there was no impact to flight readiness, or risk to safe operations," said astronaut Ellen Ochoa, who is also deputy director of the Johnson Space Center.
"We really can't say too much else due to medical privacy."
The few details available seem to suggest a simple mistake rather than a binge drinking episode.
The incident didn't occur on a launch day, and survey respondents were unanimous in indicating that none of them had ever observed an intoxicated crew member on a launch day.
Nonspecific reports of astronauts who were drinking or hung over on launch day first surfaced last summer in a report by a panel of outside experts looking into NASA's astronaut health care policies.
That report was commissioned after astronaut Lisa Nowak's arrest last year after allegations that she assaulted a romantic rival.
NASA officials wanted to find out if managers, co-workers or doctors could have done anything differently to detect any behavioral or mental health problems that she may have shown.
In a full investigation concluded in August, Bryan O'Connor -- NASA's chief of safety and mission assurance -- asked astronauts from every flight crew going back to the early 1990s to go on the record in identifying any crew mates who might have been impaired by alcohol on launch day.
He failed to turn up any additional details regarding the drinking allegations, and NASA Administrator Michael Griffin wrote them off at the time as an "urban myth."
However, agency managers commissioned the survey to try to further identify problems that might need fixing related to astronaut health care and safety, and to ask astronauts again about the drinking issues -- this time with the protection of anonymity.
"We've asked every which way that we can think of, and and we still really haven't uncovered anything that led us to believe that is an issue," Ochoa said.
Overall, the survey paints a sunny picture of life in the astronaut corps. Respondents widely agreed that astronauts generally have a candid and trusting relationship with the flight surgeons who care for them. Astronauts voiced ongoing reservations that medical information be kept private.
Both groups say they feel comfortable raising concerns about astronauts and potential flight safety issues to management without fear of retribution or ostracism.
Some astronauts indicated they were troubled by the subjective nature of the crew assignment process, voicing some concern that raising safety issues could affect future flight assignments.
Managers say they are working on developing new procedures to clarify how flight assignments are made and give astronauts more individual feedback as to why they do or do not receive a flight assignment.
But the upbeat nature of the survey stands in contrast to the review authored by the panel of independent experts and released last July.
At a press conference in Washington on the day of the release, lead author Dr. Richard Bachmann Jr., a colonel in the Air Force, outlined a more complicated state of affairs.
"Members of the medical and astronaut communities raised significant concerns regarding barriers to communication," he said.
"They described instances where medical personnel or fellow astronauts raised concerns about an astronaut's fitness for flight due to astronaut use in the immediate preflight period, and these concerns appeared to them to be disregarded or overridden."
He recommended NASA conduct exactly the sort of anonymous survey released Wednesday.
Rep. Mark Udall of Colorado, who chairs the Space and Aeronautics Subcommittee, released a statement suggesting NASA still has work to do.
"While the anonymous survey released today provides some useful data, NASA's action plan for addressing the problems identified last year is still unavailable," he said.
"NASA needs to provide that plan expeditiously if Congress is to be confident that NASA is serious about dealing with concerns raised by Col. Bachmann and others." E-mail to a friend