August 11, 2007—NASA is evaluating what appears to be a three inch by three inch gouge to a critical black heat protection tile on Endeavour’s belly. That portion of the Shuttle endures heat of up to three thousand degrees during re-entry into the atmosphere at mission’s end. You have to squint to see the damage in this photo from NASA, it’s in the lower left hand corner, right above the word "into" in "into the atmosphere" in this paragraph.

The fact that the apparent damage is near the main landing gear wheel well under the right hand wing is disquieting for those close to the Columbia disaster. When that Shuttle suffered a broken heat shield on the leading edge of its left hand wing in 2003, NASA engineers say superhot gases poured through the breech during re-entry, through the innards of the wing, and out the main landing gear wheel well door. During the perilous trip through the atmosphere, Columbia’s computers ordered the Shuttle to bank back and forth to reduce its speed. Engineers say, during these maneuvers, additional aerodynamic drag on the wing put the Shuttle into a slow roll onto its back. The top of the Shuttle isn’t designed to take that kind of heat and the spacecraft broke up.

What NASA wants to establish with Endeavour’s damage is how bad it is. The Shuttle is an aluminum aircraft with tiles glued on. Aluminum melts at three hundred degrees, so as long as re-entry heat at the damage spot doesn’t exceed that level, NASA may be comfortable bringing the Shuttle back as is. Otherwise, spacewalkers may be asked to apply a heat resistant paint on the divot, screw a protective plate on the break, or squirt a pink compound called "goop" into the cavity.

More to come.

Photo courtesy of NASA