The shuttle orbiter Columbia's left wing was increasingly compromised by the penetration of 2000F reentry plasma starting over the Pacific Ocean 400 mi. off the coast of California, early in the hottest phase of its disastrous reentry Feb. 1, according to new data released by NASA.

This information provides more detail on sensor readings and when they occurred relative to the orbiter's ground track during the reentry, which ended in the loss of Columbia and her seven crewmembers over north central Texas.

One critical finding is that a breach in the left wing-along its leading edge, its landing gear door or seals-would had to have occurred for temperatures in the left wheel well to rise as they did in the final seconds before breakup began, according to data developed by a NASA thermal analysis team. The data were provided to the independent Columbia Accident Investigation Board headed by Adm. (ret.) Harold Gehman.

The analysis is extremely important because it indicates that missing thermal tiles alone on the wheel well door would not cause a temperature rise like that detected before breakup, officials in Houston said.

Sources outside the board noted that it it is increasingly likely the breach in the wing structure was not specifically in the wheel well area, although sensors in the wheel well and on the trailing edge of the wing provided some of the first signs of trouble.

They said the nexus of data from the accident continue to implicate the impact of insulation from the Lockheed Martin-built external tank on the left wing as part of a chain of events that could have resulted in a breach of wing structure.

The Boeing debris impact analysis highlighted both the leading edge of the wing and an area on the gear door as significant impact areas.

How the breach occurred and its location remain key questions for the board. But "additional analysis is underway looking at various scenarios in which a breach of some type, allowing plasma into the wheel well or elsewhere in the wing could occur," according to a statement from the board.

It specifically noted that there are no data to support a premature deployment of the left landing gear, contrary to widespread media reports late last week.

If debris had damaged the wing's leading edge reinforced carbon-carbon structures or deeply gouged tiles, allowing hot plasma to penetrate and erode the underlying aluminum, an increasingly larger path for the plasma to enter the wing could have been created (AW&ST Feb. 10, p. 22).