No damage found during heat shield inspections
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 6, 2006
Preliminary assessment of the shuttle Discovery's heat shield after a dramatic end-over-end flip today while approaching the international space station shows no signs of appreciable damage to the ship's fragile heat shield tiles from debris impacts during launch, officials said.
John Shannon, chairman of NASA's Mission Management Team, said a full assessment of the 352 photographs taken by station commander Pavel Vinogradov and flight engineer Jeff Williams would take another day to complete.
But the initial assessment of laser surveys of the wing leading edges and nose cap carried out Wednesday, and a quick-look at the heat-shield tiles today showed no signs of any significant problems.
"The early look at the tile from the rotational pitch maneuver ... showed there were no tile areas that exceeded our criteria to go look at with a focused inspection."
He said the heat shield appeared in such good shape it was "somewhat of a surprise, but a very pleasant surprise."
Engineers planned to work through the night, analyzing the imagery in detail, to identify possible areas to examine Friday morning during so-called focused inspections. A four-hour block of time is built into the crew's flight plan to use a long boom equipped with a high-resolution camera to inspect anything out of the ordinary.
At least two gap fillers have been seen protruding from surrounding tiles. Gap fillers are heat resistant spacers used to prevent adjacent tiles from rubbing against each other when the shuttle's aluminum skin flexes during launch. One of those is toward the outboard edge of the left wing while the other is just in front of a propellant feedline access door near the back of the orbiter.
During Discovery's flight last year, a spacewalking astronaut was asked to pluck out two protruding gap fillers to ensure smooth aerodynamic flow over the shuttle's belly during entry. Material protruding above the tiles can trigger turbulent airflow, which generates more heat.
Shannon said engineers have not yet decided what, if anything, might need to be done about the two gap fillers seen so far in the current mission, or what to do about a very small bit of unidentified material just behind the nose cap of the shuttle.
But overall, he said, Discovery is "a really clean vehicle, we're extremely happy with the performance of all the systems that we've looked at so far."
Shannon down played any concern about a large piece of foam insulation that peeled away from an area just in front of an ice-frost ramp on Discovery's external tank. During a briefing Wednesday, Shannon said the piece measured roughly eight by 10 inches. Today, he said additional analysis showed the missing foam measured 12.3 inches by 14.2 inches.
Engineers say the foam broke apart into a half-dozen pieces as it peeled away. And it came off after Discovery was out of the thicker regions of the atmosphere. For foam to pose a threat to the shuttle, it most separate in the lower atmosphere, which causes the lightweight material to rapidly decelerate. The shuttle can then ram into it at a high relative velocity.
Shannon said even if the foam in question came off earlier in Discovery's climb to space it would not have caused any problems.
"They're still working on the mass," he said. "The prediction was between a half inch and an inch thick, which makes it very light, very small. The initial report from the external tank project was we did not violate any limits we had set pre flight."
He said engineers expected to calculate actual mass estimates over the next two days.
"My initial thought, and what the ET project was thinking, was even if it had come off in the time of aerodynamic concern before 135 seconds, it still would not have been an issue," Shannon said. "It was absolutely not a surprise at all to see that. That is consistent with the behavior we've seen from the ice-frost ramp area in the past."