CAPE CANAVERAL, Fla. — NASA has cleared space shuttle Atlantis for liftoff Monday on a trip to stock up the International Space Station with several years' worth of spare parts.

Mission managers gave the go-ahead Saturday as forecasters put the odds of good launch weather at 90 percent, about as good as it gets.

Atlantis will deliver nearly 30,000 pounds of pumps, storage tanks, gyroscopes and other spare parts, along with six astronauts who will unload everything.

The goal is to take up as many large parts as possible, to keep the space station running for five to 10 years after the shuttle program ends next fall. Some of the pieces are too big to fit in any other spacecraft.

With the flight lasting 11 days and including three spacewalks, it might appear as though NASA is slacking off given the mega-missions of the past year or so, said Mike Moses, chairman of the mission management team. He told reporters, however, that those two-week flights with four or five spacewalks were "unbelievably challenging ... and it is certainly not the norm."

A stockpiling mission like this one does not require lots of spacewalking work, Moses said. The astronauts, in fact, will use some of their time outside to get ready for the next shuttle flight in February, when a new window-domed room will be taken up.

Only six shuttle missions remain, including this one.

Atlantis will bring back astronaut Nicole Stott, who has been living on the space station since the end of August. Also returning on the shuttle will be a broken piece of the station's water-recycling unit. The part that converts the astronauts' urine into drinking water has failed; engineers want it back so they can fix it and send it back up on the next shuttle flight.

The inability to recycle urine will not interfere with the shuttle's visit, Moses said.

Liftoff remains scheduled for 2:28 p.m. Monday, even though an unmanned rocket did not take off Saturday morning with a communication satellite as planned.

That's because the Atlas rocket has a technical problem that cannot be fixed quickly.

A Sunday launch attempt would have delayed the shuttle flight by one day.