A 17 1/2-ton truss segment is shown over the space shuttle Atlantis after it was removed from the cargo bay for installation on the international space station. Astronauts will begin a spacewalk to install the truss today.

Houston ? 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 1/2 years Monday and now will conduct three spacewalks to install the giant new section.

Atlantis’ heat shield is so trouble-free that NASA engineers late Monday decided they didn’t 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 today.

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 1/2-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.

The flight marks the first time since the 2003 Columbia disaster that NASA has resumed assembly of the orbiting space lab. The newly delivered piece consists of a truss and electricity-generating solar panels that can rotate with the movement of the sun – and the parts have been waiting for launch for several years.

“It’s kind of like seeing your kids grow up; it’s a sense of pride,” said space station deputy manager Kirk Shireman, describing how he felt now that the addition was finally part of the space station. “We’ve been babying it and protecting it and improving it.”