Atlantis' docking with the space station was done by executing a "back flip" maneuver that leaves the shuttle's underbelly facing the space station, where crew members can investigate its condition, NASA said.  After checking for leaks, the crew opened the hatches between the two vehicles shortly after 12 p.m. ET.  "It was really moving to see the final docking of the shuttle to the space station," Cain said, adding that it was the 12th such time Atlantis has done so.  The crews of Atlantis and the space station also will research the potential for a space refueling system.  Meanwhile, NASA is monitoring a piece of space debris that could be headed toward the space station, Cain said Sunday afternoon.  Data indicates that the point of closest approach would occur on Tuesday, the same day as a scheduled space walk by shuttle crew members, according to Cain.  "However, we don't really have a good (probability of collision) on it yet," said Cain, who cautioned that the size of the object is still not known.  More information is expected to be released later Sunday or Monday, he said.  A space-debris incident nearly two weeks ago prompted the crew of the International Space Station to take shelter inside two Soyuz capsules when it came within 1,100 feet of the station.  NASA Administrator Charles Bolden, speaking to CNN's Candy Crowley on Sunday, said the conclusion of the American space shuttle program doesn't mean the United States is ceding the space race to Russia.  "American leadership will persist for the foreseeable future, I can guarantee you that," Bolden said. In addition to taking cargo to orbit next year, NASA is working to partner with commercial interests in developing a crew vehicle, he said.  "We are hopeful in starting to ask for proposals from industry (in the) early part of next year," he said.  A recent call from President Barack Obama re-emphasized aggressive goals for NASA, including exploration beyond lower orbit and into deep space, Bolden said.
Atlantis docked with the International Space Station on Sunday for a week-long rendezvous, two days after blasting off on a historic flight marking the final liftoff of the U.S. shuttle