In very frank terms, Daugherty's e-mail explained a variety of scenarios that could face flight controllers Feb. 1 if the analysts were wrong and the landing gear door heat shield was breached during the fiery descent to Earth.

Daugherty was clear to point out two different times in his message that he was looking at worst possible outcomes and "I don't really believe things are as bad as I'm getting ready to make them out."

"Admittedly this is over the top in many ways but this is a pretty bad time to get surprised and have to make decisions in the last 20 minutes (of re-entry)," Daugherty wrote, noting mission controllers should study some options ahead of time because the warnings might come at the last minute.

Then his analysis explained what could happen with rising heat in the left wheel well.

"The reason might be that as temps increase, the wheel (aluminum) will lose material properties as it heats up and the tire pressure will increase. At some point, the wheel could fail and send debris everywhere," Daugherty wrote.

"It seems to me with that much carnage in the wheel well, something could get screwed up enough to prevent deployment and then you are in a world of hurt," he continued.

Daugherty and others who actually wrote the electronic messages could not be reached for comment Wednesday. The space agency instead provided interviews with Cain and the chief flight controller, Milt Heflin, who both said they were not aware of the e-mail conversations prior to Feb. 1.

Telephone messages left with the employees involved were not returned. One of the employees' voice mail greetings indicated he is on leave.

"We do this all the time," Cain said in dismissing the e-mails as a major concern. "We train for the worst case. You go down a logic path that says, 'If we're totally wrong, that leads to some consequence' so I have some opportunity to put some shelf life on my thought process so that, in the control room, I've thought through that point."

In this case, Cain said he did not know Daugherty's specific concerns and, asked if he would like to have known, he said, "No."

In the six to seven minutes before mission controllers lost contact with Columbia on Feb. 1, NASA has said temperatures were rising and instrumentation was failing in and near that left landing gear well. Other instrumentation further back in the left wing failed too, but shuttle program manager Ron Dittemore has noted the cables leading to those sensors run adjacent to the left wheel well, too.

He said investigators would be tracing the cabling to common points to try to determine where any heating problems might have originated.

One of Daugherty's concerns was that rising heat inside that wheel well could eventually explode the tires, setting off a chain reaction. "The resulting loads on the gear door (a quarter million pounds) would almost certainly blow the door off the hinges or at least send it out into the slip stream - catastrophic. Even if you could survive the heating, would the gear now deploy?"

Daugherty questioned whether Columbia, in that condition, could even reach the Florida runways.

Trying to prepare the Houston controllers for decisions they might have to make in those worst-case scenarios, Daugherty posed several questions. One was whether Houston was considering a wheels-up, belly landing for the orbiter if the landing gear did not deploy. He asked if that happened whether they still planned to land at Kennedy Space Center in the event of problems.

"If a belly landing is unacceptable, ditching/bailout might be next on the list," Daugherty wrote. "Not a good day."

The bailout procedures discussed there would not have applied at 200,000-plus feet where Columbia broke up but much lower and only had the orbiter somehow survived the high-altitude, superhot part of re-entry.

Had it gotten lower, there are some emergency procedures in place. The astronauts use a pole in the crew compartment to slide away from the flying ship and then parachute away from it -- leaving the orbiter to crashland empty.

NASA has never had to use the contingency system, but crews practice it. Cain said that would have been among his options if presented with the precise scenario laid out by Daugherty in his e-mail, but quickly noted the scenarios were highly unlikely as was getting the ship down to a safe level where the crew could ditch her anyway.

As he wrote the e-mail that day, Daugherty said engineers at Ames Research Center were conducting a variety of simulations at a landing simulator at the California center. He said it would be easy for them to work on specific simulations for Columbia, but NASA could not say Wednesday if the simulations were done or not.

In response to the Daugherty e-mail, Houston controller David Lechner, of shuttle contractor United Space Alliance, wrote: "Like everyone else, we hope that the debris impact analysis is correct and all this discussion is mute (sic)."

Another Langley official replied to his colleagues, including Daugherty, "looks like they believe all has been addressed."

Cain and his boss, Milt Heflin, said that is exactly right. They said the e-mails never reached them and Cain said that is normal. Controllers will often continue discussing what-if scenarios even after higher-up engineers have made a final decision that something is no longer a safety issue. They are taught to be devil's advocates and to be thinking ahead of the vehicle so they can be prepared for a wide range of potential surprises.

Heflin said he could not characterize the Houston controller's response that the team would "hope" the debris analysis was correct. He said that did not necessarily mean that they disagreed with that analysis, but noted he could not read the controllers' minds. Heflin and Cain did say, however, that they knew that all members of the flight control team agreed with the earlier decision that the debris during launch did not threaten safety.

NASA also issued a written statement along with the e-mails: "The interchange is typical of what takes place during a mission. Often, the broader NASA community is involved in evaluating potential issues. The Langley engineer identified no new concerns or failure conditions that had not previously been examined by Johnson engineers and flight controllers. For this reason, there was no reason to elevate the points raised in the discussion to the Mission Management Team."

NASA also clarified its earlier statement that the Johnson controllers first contacted Langley on Jan. 27. Now the agency says the initial inquiry from the controllers to Langley was on Jan. 28. Cain said there were other discussions but NASA is yet to release any other e-mails about the situation, if any exist. Cain and Heflin said that the people in the mission control room were united in their belief the debris analysis was correct and the landing gear doors and other parts of the heat shield were not harmed enough by debris to threaten Columbia or her crew.

In two reports during the 1990s, university researchers warned NASA that tiles in the area of the landing gear wells were among those most succeptible to failing and, if they did fail, posed the greatest risk of losing an orbiter. The report said foam falling from the tank and weakening adhesive bonds were the prime reasons that tiles could come off and threaten the orbiter during re-entry.

Florida Today writers Chris Kridler at Kennedy Space Center and Kelly Young at Johnson Space Center contributed to this report.

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