HOUSTON (AP) – Endeavour’s astronauts woke up Saturday to the soulful tunes of “Gravity” by John Mayer and started to prepare for the mission’s first spacewalk to install a cube-shaped addition onto the international space station’s frame.

“Seems kind of appropriate,” said crewmember Charles Hobaugh, whose family dedicated the song to him. “We’re excited to get out to a great day with the (spacewalking) team.”

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 won’t know for sure until they get more information.

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,” Mr. 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 the spacewalk Saturday, 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. Messrs. Mastracchio and Williams will then work on removing launch restraints and bolting the segment into place.

The addition will act both as a spacer between a pair of the station’s power-generating solar arrays and as a channel through which lines of electricity, data and cooling liquid will run.

The midday jaunt outside the orbiting outpost is set to last for about 6½ 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, Ms. Morgan’s crewmates and the station residents photographed her floating through, like paparazzi around a movie star.

Ms. 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. Morgan 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.

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AP Aerospace Writer Marcia Dunn contributed to this report from Cape Canaveral, Fla.

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