HOUSTON - A senior structural engineer at the Johnson Space Center here wrote in an e-mail message to his managers during the flight of the shuttle Columbia that he and other engineers saw "big uncertainties" about the extent of damage when debris hit it.
The engineer said NASA should "beg" other agencies for help in photographing the spacecraft.
In his message Jan. 21, the engineer, Alan R. Rocha, offered specific suggestions on revising the re-entry plans, depending on the damage found. Rocha said that without the pictures, it would be impossible to know how to adjust the re-entry.
The message, sent five days after the shuttle was launched Jan. 16, is the first internal NASA communication to show that engineers foresaw a possible need for different options for re-entry and suggested discussing those alternatives. It indicates that some NASA engineers thought they would have to devise a plan to rescue the spacecraft with an improvised repair, as they did for the Apollo 13 mission in 1970.
Senior NASA officials have said that they did not shift plans because they concluded that there was no threat of serious damage and that the standard re-entry pattern was the best available.
A central question in the investigation of the break-up on Feb. 1 is if NASA and its contractors were aggressive enough in obtaining information about the damage from debris. Engineers suspect that debris that hit the shuttle 81 seconds after liftoff and struck protective tiles on its underside or the reinforced carbon-carbon composite on the front edge of the wing.
In a report dated Jan. 23, five engineers of Boeing, a NASA contractor, said the debris had not caused life-threatening damage. Senior NASA officials have said the Boeing report dispelled any major doubts that they had about the risks posed by the damage.