The international space station will be one piece closer to completion Saturday, after two spacewalking astronauts install a cube-shaped spacer onto the orbiting lab's frame.
Meanwhile, back on Earth, NASA continued to review data on a worrisome gouge on the belly of the docked shuttle Endeavour. The damage, about 3 inches square, appears to have been caused by ice that broke off the fuel tank a minute after liftoff, though managers will not know for sure until they get more information.
NASA is especially eager to see the zoom-in digital pictures and video collected during this backflip, because of concern over three pieces of foam insulation from the external fuel tank that may have struck Endeavour during Wednesday's launch. Two are believed to have hit the shuttle's right wing.
Mission managers do not suspect any critical damage, noting the three foam fragments were probably too small and one came off too late in the launch to pose any threat. But they do not want to dismiss the possibility of damage, especially to the vulnerable wings, which is precisely what happened during Columbia's doomed mission four years ago.
Wednesday's launch blasted teacher-turned-astronaut Barbara Morgan and her six crewmates into space for a two-week mission.
The shuttle astronauts will inspect the gouged area more closely on Sunday using the shuttle's robotic arm and laser-tipped extension boom. If the damage is deep enough, they may need to patch it during a spacewalk, said John Shannon, chairman of the mission management team.
"What does this mean? I don't know at this point," Shannon said Friday.
Damage to the shuttle's skin, which protects it from the intense heat of re-entry into the Earth's atmosphere, has become a focus of the space agency since the Columbia disaster in 2003.
During Saturday's spacewalk, the first of the mission, spacewalkers Rick Mastracchio and Dave Williams will provide on-the-scene guidance while astronauts inside the space station use a crane-like robotic arm to maneuver the 2-ton, $11 million segment into place. Mastracchio and Williams will then work on removing launch restraints and bolting the segment into place.
The midday jaunt outside the orbiting outpost is set to last for about 6 1/2 hours.
On two spacewalks planned for later in the mission, astronauts will install a giant storage platform for spare parts and a new gyroscope that controls the station's orientation, replacing one that is broken.
The space shuttle reached the space station Friday afternoon and docked after doing a 210-mile-high backflip so the space station residents could photograph the often-nicked shuttle belly.
After the hatch between the two spacecraft opened, Morgan's crewmates and the station residents photographed her floating through, like paparazzi around a movie star.
Morgan has waited two decades for this trip into space.
The former Idaho elementary schoolteacher was Christa McAuliffe's backup for Challenger's tragic mission in 1986. She was invited by NASA into the astronaut corps 12 years later. The Columbia disaster further delayed her going on a mission to space.
NASA is testing a new system that draws power from the space station to the docked shuttle, giving them the ability to prolong the length of missions. It seems to be working so far and mission managers will decide Sunday whether they feel comfortable stretching the flight from 11 days to 14 days, during which the shuttle would be docked for a record 10 days. A fourth spacewalk will be added, if the flight is extended.
Endeavour is delivering several new space station parts, most notably a 2-ton square-shaped beam that will be hooked up to the orbiting outpost on Saturday. The astronauts also will install a giant storage platform for spare parts and a new gyroscope that will replace one that is broken.
Of the 10 people aboard the joined spacecraft, Morgan is clearly the attention-getter. The former Idaho elementary schoolteacher was Christa McAuliffe's backup for Challenger's short-lived mission in 1986 and was invited by NASA into the astronaut corps 12 years later. Columbia's catastrophic re-entry in 2003 further delayed her trip into space.