Avatar Posted by bear 512 days ago (http://www.spaceflightnow.com)
Category: Science Discovery Environment | Tags: shannon tile damage threat astronauts
The foam-damaged heat-shield tiles on the belly of the shuttle Endeavour do not represent a Columbia-class threat of catastrophic failure during re-entry, the chairman of NASA's Mission Management Team told reporters today. John Shannon said the issue is more a matter of whether post-landing repairs might be needed that could delay Endeavour's next flight or whether it might make more sense to stage a relatively simple spacewalk repair job to give the shuttle additional margin during re-entry.

"We're not talking about catastrophic damage," Shannon said. "But if I have to pull off five or six tiles (after landing) and put a doubler on some structure, replace a rib or anything like that, that's going to increase my turnaround time between (flights) and I'd like to avoid that if possible, if I have an EVA that I think is easy to execute. Now all of that assumes we come back and show that we would have localized heating that could cause some damage underneath and we haven't done that yet."

Asked a second time about the threat represented by the tile damage, Shannon said "this is not a catastrophic loss-of-orbiter case at all. This is a case where you want to do the prudent thing for the vehicle."

The damage was caused by a softball-size piece of insulation, possibly mixed with ice, that broke away from a propellant feedline bracket on the side of Endeavour's external tank 58 seconds after blastoff Wednesday. The debris hit an aft strut at a relative velocity of 205 mph. Surprisingly, the debris bounced off the strut and a large piece hit the belly of the orbiter at a relative velocity of about 150 mph. Shannon said engineers were surprised by the ricochet, believing a chunk of foam or ice would break up into numerous small pieces rather than bounce off a strut as the debris in question actually did.
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