Atlantis and its crew of seven astronauts touched down at 9:44 am (1444 GMT) at the Kennedy Space Center in Florida, under mostly sunny skies.

During their 11-day mission, Atlantis delivered and equipped the space station with nearly 30,000 pounds (13,608 kilograms) of critical spare parts intended to ensure safe and scientifically productive operations well after the final shuttle flight, scheduled for late September 2010.

The bulky spare gyroscopes, thermal control system components, oxygen tank and robot arm hardware hauled aboard Atlantis to the orbital outpost exceeded the carrying capacity available on the short lineup of rocket launchers capable of reaching the station.

"We had a truly amazing mission," Atlantis commander Charlie Hobaugh said from the coastal runway. "Part of it was luck and part of it was pure great skill and workmanship in getting Atlantis ready for us."

With the assembly of the space station nearly complete, just a handful of shuttle missions remain. Endeavour's February flight will deliver Tranquility, the final habitable module of the station's US segment.

Under current planning, NASA will phase out activities aboard the station by 2016 to free up funding for a shuttle successor that can transport astronauts back to the moon and the orbital outpost.

But President Barack Obama's administration is reviewing options developed by a White House advisory panel that include extending ISS activities until 2020, an outcome supported by many in Congress and favored by NASA's international partners.

Other options under review would scrap NASA's plans to establish a base on the moon and take aim at an asteroid and other destinations humans have yet to explore.

Although NASA achieved five successful shuttle missions in 2009, the most in a year since the Columbia disaster of 2003 that claimed the lives of seven astronauts, the spacecrafts seem unlikely to receive a reprieve beyond early 2011.

NASA has already instructed its contractors to halt the production of fuel tanks and solid rocket boosters for the shuttle and made other moves that have triggered hundreds of layoffs.

"The important thing is to really take the missions one at a time and not rest on our laurels," Bill Gerstenmaier, NASA's chief of space operations, told reporters after Friday's landing.

"When we start to think things are going well, that is when we start slipping a little bit and getting into trouble. We need to avoid that tendency."

Even if the Obama administration extended the missions, it would likely take three years from the date of a directive to reopen productions lines before shuttle launchings could resume, he added.

During a prolonged debate over the fate of NASA's successor to the shuttle -- the under-funded Orion crew exploration vehicle and Ares 1 rocket, the US space agency agreed to pay Russia for the transportation that will assure American astronauts have access to the space station.

Nicole Stott, who returned to Earth aboard Atlantis after three months aboard the station, is the last American scheduled to make the round trip journey aboard a shuttle.

After the February mission, the final four shuttle flights will carry more supplies and scientific research gear to finish out a dozen years of construction and outfitting of the outpost, which has grown larger than an American football field.

While the shuttle was parked at the station, the Atlantis astronauts hustled through three spacewalks and took on extra tasks.

They teamed with five US, Russian and European astronauts aboard the station to establish power, cooling and airway connections ahead of Tranquility's arrival and set up new external communications systems to ease future maintenance of the outpost.

Astronaut Randy Bresnik, who traveled to space for the first time, closely monitored his wife, Rebecca, who went into labor and gave birth to a daughter, Abigail Mae, during a day-long break between his two spacewalks.

"It's the most amazing three days of my life," the Marine Corps aviator said. "I look forward to getting home and seeing her for the first time in person."

Bresnik, only the second US astronaut to become a parent during spaceflight, will reunite with his family on Saturday, when the astronauts fly to Houston, where they live and train at NASA's Johnson Space Center.

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