In the aftermath of a damaging report on drinking by NASA astronauts, the space agency is implementing a 12-hour no-drinking policy before launch.

An independent panel revealed Friday that according to interviews, two occasions NASA astronauts were allowed to fly despite the fact they had been drinking heavily and even though space agency doctors had warned safety could be at risk.

One astronaut flew on a Russian spacecraft after drinking heavily and another was cleared to launch on a shuttle, Col Richard Bachmann, head of the panel that investigated astronaut health, said Friday.

"In none of these can we say factually they did or did not occur," he told a news conference in Washington by telephone.

NASA said it isn't aware of any astronauts who were drunk before a flight but that it is investigating.

During Friday's news conference, NASA deputy administrator Shana Dale said the agency will act immediately on the more troubling aspects of the report as it pertains to alcohol abuse.

Dale said NASA's policy that prohibits drinking within 12 hours of an astronaut flying a training jet will now be applied to all spaceflights as an interim measure until a more permanent policy can be worked out.

Dale also said NASA has "had discussions with the crew commander of next shuttle mission and its flight surgeon," and communicated the agency's concern about alcohol use by astronauts.

The shuttle Endeavour is set for launch on Aug. 7.

NASA will also conduct an internal safety review and "recommend corrective actions," Dale said, noting that the space agency also gives great weight to the panel's recommendation of an astronaut code of conduct.

Short on details

The panel's report offered few details, giving no information about when the drinking took place, how many were involved, or whether the incidents involved NASA training jets, the space shuttle or the Russian Soyuz spaceship.

It found NASA officials let astronauts fly despite the fact flight surgeons and other astronauts raised concerns that safety could be jeopardized by their condition.

The panel's report also contained anecdotal reports from other astronauts and flight surgeons that crew members often engaged in heavy drinking just prior to flights and said alcohol is consumed in crew quarters where astronauts are quarantined for three days before launch.

"Two specific instances 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 panel reported.

"However, the individuals were still permitted to fly."

At the Friday news conference, Dale said the panel has failed to provide details of the allegations. Bachmann said it wasn't the panel's job to investigate allegations and that NASA would have to follow up.

Dale suggested the reports of alcohol use are the exception to the rule, and the entire organization shouldn't be judged by the actions of a few.

"For almost the entire history of the astronaut core, our experience has been that NASA's astronauts conduct themselves with integrity, professionalism and a desire to bring honour to America and America's space program," she said.

Bachmann, an air force aerospace medical specialist, said the panel deliberately didn't seek out details. His main concern is that flight surgeons were ignored.

"There's certainly no intent to impugn the entire astronaut corps," Bachmann said. "We don't have enough data to call it alcohol abuse. We have no way of knowing if these are the only two incidents that have ever occurred in the history of the astronaut corps or if they're the tip of a very large iceberg."

Only four of the report's 12 pages dealt with alcohol use by astronauts.

The report also found that NASA is simply not structured in a way that allows officials to deal with alcohol use by astronauts.

"The medical certification of astronauts for flight duty is not structured to detect such episodes, nor is any medical surveillance program by itself likely to detect them or change the pattern of alcohol use," the panel wrote.

They recommended a higher standard of accountability for alcohol use and said policies must be introduced to deal with the problem.

The report was ordered after astronaut Lisa Nowak was arrested on charges of attempting to kidnap one of her colleagues in a bizarre love triangle.

With files from The Associated Press