One of the two spacewalking astronauts who was to help install the $2 billion European science lab, Columbus, was pulled from the job because of a non-life-threatening condition. The installation won't take place until Monday.
NASA officials would not say why German astronaut Hans Schlegel was being replaced, but Atlantis' commander, Stephen Frick, requested a private medical conference with flight surgeons shortly after reaching the space station.
"I will just say it's not going to impact any of the objectives of this mission," said John Shannon, chairman of the mission management team. "It will cause us to rearrange a few activities."
Shannon refused to elaborate, citing medical privacy, but noted that it was not a life-threatening condition. When asked by another reporter if it was contagious, he said: "You guys can fish all day, but I won't bite."
Schlegel, 56, a two-time space flier, did not appear to be sick when he floated inside the space station and took part in a safety briefing, but he seemed quiet. He was seen on camera for only a few minutes.
At one point, space station astronaut Daniel Tani is heard asking someone, "What did you do to your voice?"
NASA's public affairs office refused to speculate whether the question was directed to Schlegel. But it would be a safety issue if a spacewalker could not speak.
Schlegel was supposed to venture outside with American Rex Walheim on the first two spacewalks. His status on the second spacewalk, on Wednesday, was still uncertain.
The Columbus lab should have been unloaded from Atlantis and attached to the space station on Sunday, with two spacewalkers outside to help. Mission Control informed the astronauts about the delay just a few hours after the space shuttle and the station joined up.
NASA said Schlegel's crewmate, American Stanley Love, would take his place. Love trained for the work as a backup, just in case, and already was assigned to the mission's third spacewalk, along with Walheim.
It was a rare and unsettling change in plans for NASA, which typically prepares for every aspect of a shuttle mission - particularly spacewalks - for months and even years.
The delay in installing Columbus and carrying out the first spacewalk prompted NASA to add a 12th day to the mission. Yet another day could be added; NASA had hoped to spend an extra day at the space station to help set up Columbus.
The two spacecraft linked up as they passed more than 200 miles above Australia. Just over an hour later, the 10 space travelers - seven shuttle astronauts and three station residents - threw open the hatches, laughing and shouting.
Just before docking, Atlantis did a 360-degree backflip so station commander Peggy Whitson and her crew could photograph the shuttle's thermal shielding. Nearly 300 photos were beamed back to Earth so engineers could look for any signs of launch damage.
Mission Control requested extra pictures of a torn thermal blanket on Atlantis' right orbital maneuvering system pod, back near the tail. The small tear was along a seam, and occurred during the launch, said flight director Mike Sarafin.
Engineers were analyzing the tear and whether it posed a hazard for re-entry at flight's end. The exact size of the peeled-up section was unknown, but it appeared to be smaller and less worrisome than one that required spacewalking repairs last June. Coincidentally, that tear was in a blanket on Atlantis' left orbital maneuvering system pod.
"It's probably not that big of an issue, but we're off looking at it," Sarafin said.
The photos of the shuttle's thermal shielding tiles are standard procedure, ever since the destruction of Columbia in 2003. Columbia's wing was gashed at liftoff by a chunk of fuel-tank insulating foam. Only a small amount of foam is believed to have come off Atlantis' tank, and none of it appeared to seriously damage the shuttle.
Saturday was Whitson's 48th birthday, and the shuttle astronauts wished her all the best. She said Columbus' arrival was a great way to celebrate.
Europeans have waited an agonizingly long time to see Columbus in orbit.
The original plan called for Columbus to be launched in 1992 to mark the 500th anniversary of Christopher Columbus' voyage to the New World. But years passed as NASA redesigned the space station. Then station construction ended up being stalled, and then the shuttle fleet was grounded for 2½ years following the Columbia tragedy.
Atlantis will remain at the space station until at least next weekend.
For more information on the STS-122 mission visit the NASA Web site: spaceflight.nasa.gov