The crews of Atlantis and the international space station greeted each other with hugs and handshakes Sunday after the space shuttle arrived at the orbiting outpost.
But amid the smiles and salutations, engineers in Houston 220 miles (350 kilometers) below started evaluating whether a peeled-back thermal blanket should be fixed by astronauts.
A decision likely will be made in the next day or two, and if the answer is to fix it, another decision will be made on whether it would be done during one of three scheduled spacewalks or during an extra, unplanned one.
Astronauts James Reilly and Danny Olivas planned to make the mission's first spacewalk on Monday to help attach a new 35,000-pound (16,000-kilogram) segment to the space station.
Engineers who had studied past damage to the blanket area, located on a pod of engines near the shuttle's tail, on other shuttle missions were uncomfortable with the safety margins of a piece of the blanket sticking out during re-entry into Earth's atmosphere, when temperatures on the shuttle's heat shield can reach as high as 2,900 degrees Fahrenheit (1,600 degrees Celsius).
Temperatures at the blanket's location typically reach only to 700 degrees to 1,000 degrees F (370 to 540 degrees C).
"The concern is that if it sticks up, you get additional heating," said John Shannon, chairman of the mission management team.
Engineers were confident the loosened blanket was caused by aerodynamic forces during launch, not by being hit by a piece of debris during lift off. "Since this wasn't an impact blow, we have high confidence that the structure beneath it is pristine," Shannon said.
The rest of the vehicle appeared to be in fine shape, NASA said. Sensors reported six hits on the wing during launch, but engineers were not concerned about them.
Hatches between the two spacecraft opened about one and a half hours after the shuttle docked with the space station, following leak checks.
"Atlantis arriving," U.S. space station resident Sunita Williams said after the traditional ringing of a bell.
Atlantis' astronauts floated into the space station's Destiny laboratory and hugged each of the station's residents, which besides Williams includes commander Fyodor Yurchikhin and cosmonaut Oleg Kotov. After exchanging greetings and receiving a safety briefing from Yurchikhin, both crews resumed working.
Before reaching the space station, Atlantis commander Rick Sturckow told Yurchikhin that shuttle astronaut Clayton Anderson was ready to relieve Williams on the station.
"Are you sure Clay is onboard?" Yurchikhin said.
"Yes we checked before we launched from Florida," Sturckow said amid laughter.
Sturckow eased the shuttle into the space station's docking port. Latches fastened the shuttle and orbiting space lab together at 3:36 p.m. ET. The shuttle's two-day chase of the space station ended above southeastern Australia.
It was the first visit this year by a shuttle to the space station. The shuttle was delivering Anderson, the newest member of the space station's crew, as well as a new segment to the orbiting outpost.
Prior to Atlantis' arrival, astronaut Danny Olivas took additional photographs from inside the shuttle of the area where the thermal blanket had peeled back. The images were sent to Mission Control for analysis.
Astronauts inside the space station also took photographs of the shuttle's belly when Atlantis was 600 feet below the orbiting outpost.
The pictures were taken when Sturckow maneuvered the shuttle into a 360-degree back-flip — part of an inspection technique instituted after the 2003 Columbia tragedy. Engineers want to make sure there is no damage from launch like the kind that doomed Columbia.
After the hatches were opened Williams and Anderson were to trade out seat liners on the Russian emergency vehicle attached to the station. The seat liner exchange marks the official replacement of Williams by Anderson as a space station resident.
The shuttle astronauts' wake-up song Sunday, "Riding the Sky," written by two Johnson Space Center employees, was dedicated to Anderson in honor of his move to the space station.
Williams will return to Earth aboard Atlantis after more than six months in space.
NASA engineers want to study more photos of the torn blanket, including images taken by cameras attached to the solid rocket boosters that separated from Atlantis after launch. On Saturday, astronauts took photographs of the thermal blanket and heat shield using a camera attached to the end of a robotic arm and boom.
Engineers can build models from the images and perform tests to determine whether the peeled-back blanket would be problematic when Atlantis returns to Earth.
Thermal blankets came unstitched during flights of Discovery in 2005 and 2006 with no problems, and thermal tiles were lost in the same area where the blanket is on Atlantis on two of the earliest shuttle flights.
If the blanket needs to be fixed, Atlantis' astronauts could trim it off, tuck it back into protective tiles or cover it with a plate held in place by adhesive goo during three planned spacewalks or an extra one that could be added.
After the Columbia disaster, a shuttle repair kit was included in all shuttle missions.
During the 11-day mission, Atlantis will also deliver to the station a new segment, which includes a third pair of solar arrays. The new addition was expected to be attached to the station Monday during the first spacewalk.
AP's Mike Schneider in Houston contributed to this report.