Washington ? One day before the Columbia disaster, senior NASA engineers worried the space shuttle’s left wing might burn off and cause the deaths of the crew, describing a scenario remarkably like the one investigators believe ultimately happened. They never sent their warnings to NASA’s brass.

The space agency released e-mails Wednesday also showing it was sufficiently concerned about possible damage to Columbia’s insulating tiles that it asked the Defense Department — then abruptly changed its mind — to take pictures of the shuttle in orbit more than one week before its breakup.

The dozens of pages of e-mails described a far broader, internal debate about the seriousness of potential damage to Columbia from a liftoff collision with foam debris than previously acknowledged. They even considered instructing the crew to bail out.

Engineers in Texas and Virginia fretted about the shuttle’s safety during its final three days in orbit, with one wondering whether officials were “just relegated to crossing their fingers” and another questioning why such dire issues had been raised so late.

“Why are we talking about this on the day before landing and not the day after launch?” wrote William C. Anderson, an employee for the United Space Alliance LLC, a NASA contractor, less than 24 hours before the shuttle broke apart.

Concerns about Columbia prompted a request six days into the mission, on Jan. 22, for the U.S. Strategic Command to take satellite images of suspected damage to the shuttle’s left wing. For weeks, NASA has denied it ever made such a request.

The space agency withdrew its informal request one day later amid fears it might have “cried wolf” and endangered future such requests, according to one e-mail.

Deciding against the satellite request, a NASA official wrote reassuringly to the Defense Department that Columbia was “in excellent shape” and that insulating foam that struck the shuttle on its mid-January liftoff was “not considered to be a major problem.”

Not everyone agreed.

Three days before the end of the doomed mission, one frustrated engineer, Robert Daugherty, asked, “Any more activity today on the tile damage, or are people just relegated to crossing their fingers and hoping for the best?” The response: “I have not heard anything new.”

Still surprised

After intense debate — occurring by phone and e-mails — the engineers, some supervisors and the head of the space agency’s Langley research facility in Hampton, Va., decided against taking the matter to top NASA managers, including William Readdy, NASA’s associate administrator for space flight.

“It was a surprise to us when the ‘what-if’ scenario played out,” said Robert Doremus, head of the mechanical systems group in Mission Control, who met Wednesday with reporters in Houston. “We were not expecting that.”

The space agency has previously said mission controllers were unaware of these midlevel talks, but it was unclear how high these concerns were expressed. NASA has maintained that senior officials had confidence in an analysis by the Boeing Co., a contractor, that the shuttle would return safely.

Yet Jeffrey Kling, a flight controller at Johnson Space Center’s mission control, foresaw with haunting accuracy what might happen to Columbia during its fiery descent if superheated air penetrated the wheel compartment.

Kling wrote just 23 hours before the disaster that his engineering team’s recommendation in such an event “is going to be to set up for a bailout (assuming the wing doesn’t burn off before we can get the crew out).” The following day, Kling was among the first in mission control to report a sudden, unexplained loss of data from the shuttle’s sensors in the left wing.

Crew not alerted

Kling said Wednesday the debate about risks to the shuttle among engineers was never passed to Columbia’s crew.

“This was just a mental exercise that we went through to ‘what-if’ the whole thing,” Kling said. “But there was no concern for the crew, and there was not any reason to ever tell him to look for gear tires going out.”

The e-mails showed the debate was triggered by a telephone call Jan. 27 to Daugherty from Carlisle Campbell, a NASA engineer at Johnson Space Center, about how re-entry heat could damage the shuttle’s tires.

Another e-mail, from R.K. “Kevin” McCluney, a shuttle mechanical engineer at the Johnson center, described the risks that could lead to “LOCV” — NASA shorthand for the loss of the crew and vehicle.

But McCluney ultimately recommended to do nothing unless there was a “wholesale loss of data” from sensors in the left wing, in which case controllers would need to decide between a risky landing and bailout attempt.

“Beats me what the breakpoint would be between the two decisions,” McCluney wrote.

Investigators reported such a wholesale loss of sensor readings in Columbia’s left wing, but it occurred too late to do anything — after the shuttle was already racing through Earth’s upper atmosphere moments before its breakup.

NASA has considered a bailout by a shuttle crew feasible only during level, slow flight at about 20,000 feet or lower. Columbia broke up at 207,000 feet while flying roughly 12,500 miles per hour.

Many of the e-mails NASA released were gathered at the direction of Ronald Dittemore, the shuttle’s program manager. With news media inquiring, Dittemore asked for copies of the e-mails “so that I can see the traffic and get a feel for the conversations.”