NASA is monitoring a piece of space junk that might come dangerously close to the shuttle-station.
The object will make its closest approach Tuesday -- right in the middle of a planned spacewalk.
Mission management team leader LeRoy Cain says the size of the space junk is unknown. He says the object might stay at a safe distance but experts won't know until Monday. If necessary, Atlantis' thrusters will move the linked craft.
Less than two weeks ago, space station astronauts had to take shelter in their lifeboats because of a piece of junk. It missed by 1,100 feet, the closest encounter yet.
This comes as Atlantis made the final docking in shuttle history Sunday, pulling up at the International Space Station with a year's worth of supplies.
The station's naval bell chimed a salute as Atlantis docked 240 miles above the Pacific.
"Atlantis arriving," called out space station astronaut Ronald Garan Jr. "Welcome to the International Space Station for the last time."
"And it's great to be here," replied shuttle commander Christopher Ferguson.
It's the final docking to a space station ever by a NASA shuttle. Atlantis is being retired after this flight, the last of the 30-year shuttle program.
Excitement grew throughout the morning -- in orbit and at Mission Control -- as the miles melted between the two spacecraft with every circling of Earth. Every landmark, or rather spacemark, of this final two-week shuttle mission is being savored.
Mission Control's lead flight director, Kwatsi Alibaruho, declared "this is it" as he gave the OK for the historic linkup.
This was the 46th docking by a space shuttle to a space station.
Nine of those were to Russia's Mir station back in the mid-1990s, with Atlantis making the very first. The U.S. and Russia built on that sometimes precarious experience to create, along with a dozen other nations, the world's largest spacecraft ever: the permanently inhabited, finally completed, 12 1/2-year-old International Space Station.
This time, Atlantis is delivering more than 4 tons of food, clothes and other space station provisions -- an entire year's worth, in fact, to keep the complex going in the looming post-shuttle era.
Ferguson was at the controls as Atlantis drew closer, leading the smallest astronaut crew in decades.
Only four are flying aboard Atlantis, as NASA kept the crew to a minimum in case of an emergency. In the unlikely event that Atlantis was seriously damaged, the shuttle astronauts would need to move into the space station for months and rely on Russian Soyuz capsules to get back home. A shuttle always was on standby before for a possible rescue, but that's no longer feasible with Discovery and Endeavour officially retired now.
Two days into this historic voyage -- the 135th in 30 years of shuttle flight -- Atlantis was said by NASA to be sailing smoothly, free of damage. Sunday's docking proved to be as flawless as Friday's liftoff.
As a safeguard, Atlantis performed the usual backflip for the space station cameras, before the linkup. The station astronauts used powerful zoom lenses to photograph all sides of the shuttle.
Experts on the ground will scrutinize the digital images for any signs of damage that might have come from fuel-tank foam, ice or other launch debris.
NASA, meanwhile, continued to bask in the afterglow of Friday's liftoff. As part of Sunday morning's mail to Atlantis, Mission Control sent up a 4-inch image of a shuttle made entirely of exclamation points.
Flight controllers joked that the city of Philadelphia -- Ferguson's hometown -- is arranging for Lincoln Financial Field to cut its turf in the shape of the crew's mission patch.
"The mayor was quoted as saying, 'As long as the NFL lockout is still ongoing and the Eagles aren't playing, we might as well use the stadium for something,"' controllers wrote in the so-called news break.
Atlantis and its crew will spend more than a week at the orbiting complex. The shuttle flight currently is scheduled to last 12 days, but NASA likely will add a 13th day to give the astronauts extra time to complete all their chores.
NASA is getting out of the launching-to-orbit business, giving Atlantis, Endeavour and Discovery to museums, so it can start working on human trips to asteroids and Mars. Private U.S. companies will pick up the more mundane job of space station delivery runs and, still several years out, astronaut ferry flights.