Worried NASA safety experts asked the Defense Department to photograph damage to the space shuttle Columbia's heat-reflecting tiles during its doomed final flight, but other space shuttle officials canceled the request before it could be carried out, according to internal space agency e-mails disclosed last week.

The U.S. Strategic Command, which routinely monitors objects in space, had "spun up" to respond quickly to the request, but was told not to proceed because NASA had concluded the tile damage posed no "major problem," the NASA e-mails state.

The reversal came before NASA engineers had finished their analysis of how serious the tile damage problem might be, the documents show. And some engineers still worried -- up to the day before the shuttle's disastrous landing attempt Feb. 1 -- that the damage might allow a stream of hot plasma to penetrate the shuttle's left wing and destroy its landing gear and other vital mechanical systems.

"If the wing is off, or has a big hole in it, you're not going to make the runway," one engineer warned Jan. 31.

The e-mails revealed that the disaster followed considerable internal debate about Columbia's safety during reentry, which NASA has largely kept hidden. It also provides fresh evidence that flight managers were ill-informed about the scope and depth of the engineers' concerns.

The warnings detailed in the e-mails were not passed along to engineers or senior NASA officials outside the Johnson Space Center, agency officials have acknowledged. Nor were flight controllers informed that an analysis of the landing risks remained incomplete on the 12th day of the 16-day mission, when they formally dismissed the problem and elected not to consider any change in the flight or landing routine.

-- R. Jeffrey Smith

This image released by the Columbia Accident Investigation Board shows the left wing of the shuttle, struck by debris on launch, on the first day of its mission.