It was not until the final moments of the space shuttle Columbia's doomed flight that its crew realized something had gone badly wrong. But even at the outset of the 16-day mission, the astronauts were told of the possibility that foam debris had damaged the orbiter's heat-resistant tiles shortly after liftoff, NASA officials say.

"The crew knew there was a potential impact damage about the same time the engineers [on the ground] did," said Michael C. Kostelnik, NASA's deputy associate administrator in the Office of Human Space Flight. "Nothing is kept from the crew."

If that is the case, Columbia's crew would also have been told the engineers' analysis of the foam debris incident: that although it may have damaged one or more tiles, even gouged them down to their "densified" layers, the flight itself and the lives of the crew were not imperiled. NASA officials continue to believe it is unlikely that the foam, a large chunk of which may have weighed just over 21/2 pounds, did enough damage to pose a significant risk.

NASA officials have repeatedly characterized the crew as confident in the course of the mission, even elated. And many of the e-mails sent by the astronauts to friends, family and the public support that portrayal.

Nonetheless, Sen. George Allen (R-Va.) said one of the Columbia's astronauts, David M. Brown, had expressed concern about the potential for debris damage to the left wing in an e-mail to his brother, Douglas, who lives in Arlington. Reached by telephone, Douglas Brown would not comment on his conversation with the senator, and NASA said it is up to the families to release private e-mails. Allen's office said the senator had not seen the e-mail to Douglas Brown.

NASA has not said if Columbia commander Rick D. Husband or any of the other astronauts expressed concern about the incident or questioned Mission Control about it.

In separate news conferences last week, Ron Dittemore, NASA's shuttle program manager, was asked twice about how much specific information the crew had received, or requested, about the debris incident.

Dittemore said he did not have those details, but was confident the crew had been fully briefed. "Our policy is that we tell the crew everything," Dittemore said Wednesday. "We don't hold anything back from the commander on the scene. He gets everything that we know. And we also provide the commander and the crew the rationale, so they have a good understanding of why we believe things are okay."

Asked again Friday, Dittemore was still unable to provide details. But he did say that mission controllers in all likelihood would have informed the crew about the incident by voice, then followed up with an e-mail message, probably with "a little bit more detail so that they can read it."

In the course of the flight, NASA officials said, the crew's main concerns were overwhelmingly related to the science experiments on board and a few annoying technical mishaps.

One such annoyance was the malfunctioning air-conditioning system in the Spacehab -- the pressurized module attached to the cargo bay -- where most of the experiments are done. At one point in mid-mission, the temperature of the Spacehab exceeded 80 degrees Fahrenheit; the rest of the time it was only slightly above normal.

"That was the only thing we were really working during the mission as a problem," said Allard Beutel, a NASA spokesman at the Johnson Space Center in Houston. "It was a very, very clean mission. They were getting an amazing amount of science data. We launched on time, and it looked like we were going to come down as scheduled."

It was only at the very end that anything seemed amiss. Eliezer Wolferman, father of the Israeli astronaut Ilan Ramon, said NASA officials told his family that the Columbia crew probably had 60 to 90 seconds of realizing something was wrong before the shuttle disintegrated.

"These seconds are always spinning around in my head," Wolferman told the London Evening Standard. "It's very difficult, as if I'm with them, and I try to imagine what they went through. One second is like 20 years. I can't explain it; it's hell, hell in the sky."

There is nothing to indicate the crew was aware of a serious problem until Husband acknowledged seeing a computer message noting a cutoff of tire pressure data on the left side.

"We see your tire pressure messages, and we did not copy your last," Mission Control told Husband.

"Roger," Husband replied. Then communications were lost.