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The addition of the 21-foot-long, 15-foot wide storage compartment left the space station 97 percent complete. The complex now has a mass of almost 1 million pounds.

On the next shuttle flight, by Endeavour next month, a huge science experiment will be installed on the outside of the space station, wrapping up the U.S. contributions. Atlantis will blast off with supplies on the final shuttle mission at the end of June.

NASA is under presidential direction to focus more on outer space, beginning with expeditions to asteroids and then Mars.

American astronauts, meanwhile, will continue hitching rides to the space station on Russian Soyuz spacecraft, at great expense. The intent is for private U.S. companies to take over those ferry operations within a few years.

Mission Control, meanwhile, monitored a piece of space junk — an old rocket part — that possibly was going to stray too close to the space station on Wednesday. Experts wanted to wait until after the shuttle’s undocking before deciding whether the complex needed to move out of harm’s way. But it was looking less likely that it would pose a concern, officials said Monday.