Using their ship's robotic arm, astronauts aboard the space shuttle Atlantis handed over the first big addition to the international space station in more than 3.5 years and now will conduct three spacewalks to install the giant new section. Atlantis' heat shield is so trouble-free that NASA engineers decided late Monday that they did not need to spend key hours Wednesday to examine the ship's skin very closely. Instead, astronauts will spend the week focusing on connecting the new addition, which starts with a spacewalk early Tuesday. But before anything could be connected, the shuttle had to deliver the giant framework to the space station in a delicately choreographed unberthing that later involved a handoff of a 17.5-ton construction piece from one robot arm to another. Both were built in Canada. "There you have it: the great Canadian handshake," said astronaut Steve MacLean, a Canadian.