The space shuttle Endeavour landed safely in Florida on Tuesday after completing a 13-day mission marred by damage to the spacecraft’s heat shield that led to a lengthy debate about whether to risk returning to Earth without fixing it.
The dinged-up spacecraft touched down at Cape Canaveral at 12:32 p.m. EDT after completing a 5.3-million-mile mission to the International Space Station.
NASA Administrator Michael Griffin said the damaged tiles “did very well on reentry.”
After examining the gouged thermal tiles on the tarmac at Kennedy Space Center in Florida, shuttle Commander Scott Kelly said he was “a little bit underwhelmed by the size of the gouge. It looked rather small.”
Two heat-resistant tiles on the underside of the shuttle were damaged on launch by insulating foam that fell off the external fuel tank. The cavity concerned experts because it cut through almost to the aluminum surface of the shuttle’s skin.
NASA engineers spent several days analyzing the damage before deciding not to send a repair team to squirt a caulk-like substance into the divot. Officials feared the repair could make the situation worse by changing the shape of the cavity, which could concentrate heat in the damage area instead of limiting it.
Although a detailed analysis of the damaged tiles will be done in the coming days, they fared better than expected in the 2,300-degree frictional heat of reentry into Earth’s atmosphere, NASA said. There was some additional erosion around the tiles but no indication the shuttle body was damaged.
Kelly said that dings and divots are just “part of the process of flying the space shuttle.” He said he agreed with the decision not to fix the damage and did not worry during reentry.
Endeavour’s crew installed a truss section to the station’s backbone, along with a storage bin and a gyroscope to replace one that failed. Four gyroscopes keep the station properly aligned.
With the addition of the truss section, the space station is 60 percent complete. “Little bit by little bit, we get the station built,” Griffin said. “It’s an awesome accomplishment.”
The mission was planned for 14 days, but the approach of Hurricane Dean toward NASA’s ground-control center in Houston caused mission managers to bring the crew home a day early.
Endeavour’s crew included Barbara Morgan, the backup on the Challenger mission to teacher Christa McAuliffe, who was killed along with her crew when the shuttle exploded during launch in 1986.
After landing, Morgan did not join the other crew members on the traditional walk-around to inspect the shuttle. She felt “a little under the weather,” Griffin said. Five hours later, Morgan had recovered enough to attend the crew news conference, wearing a red cap but still feeling rocky.
The next mission to the space station is scheduled for Oct. 23, but that could change as engineers examine the data from the damage to Endeavour’s heat shield. Newly installed cameras following the loss of the shuttle Columbia in 2003 have shown that on several recent missions, the insulating foam has come off the same spot near a bracket that holds the fuel feed line in place.
The chunk of foam that damaged the underside of Endeavour first hit a strut, then ricocheted into the underside of the shuttle. Over the coming weeks, NASA will be conducting tests to see if that ricochet was an unlucky bounce or something more problematic.
The foam shedding is believed to be caused by a buildup of ice under the foam layer that insulates the tank. Ice forms because the liquid fuel that carries the shuttle to orbit is cooled to minus 420 degrees.
One potential cause of the ice buildup is the extra hour shuttles sit on the ground after fueling but before launch. That hour was added after the Columbia accident to give ground personnel time to find any late problems.