CAPE CANAVERAL, Fla. -- Shuttle Atlantis pulled away from the International Space Station (ISS) Wednesday, leaving the Expedition Four team to its final two months in space and the outpost itself equipped to handle a major growth spurt during the next two years.

STS-110

For complete launch to landing coverage and the most up-to-date news about this assembly mission to the International Space Station click here.

With pilot Stephen Frick at the controls, a series of small springs pushed apart the shuttle and the station at 2:31 p.m. EDT (1831 GMT), almost one week after the two spacecraft were joined together.

"Atlantis departing," station flight engineer Dan Bursch called out from inside the station's Unity module as he rang the ship's bell.

The undocking took place as the two ships flew some 244 miles (393 kilometers) above the North Atlantic, just west of Ireland.

Frick slowly flew the spaceplane to a distance of 450 feet (137 meters), then executing a maneuver to have Atlantis circle the station so the astronauts could photograph their assembly handiwork and document the condition of the ISS for ground-based inspector engineers.

During the fly around both crews sent down spectacular views of both spacecraft. The new truss could clearly be seen as a major new element of the station, while views of the shuttle showed it flying over the United States from the Mexican border, over the desert Southwest, central Colorado and the Rocky Mountains, up to Duluth, Minn., Lake Superior and over Michigan.

A final separation burn from the craft's steering thrusters took place at 4:15 p.m. EDT (2015 GMT), which sent Atlantis on a course toward an early afternoon landing Friday back at the Kennedy Space Center, where the weather forecast is generally favorable.

During the shuttle's stay at the station the combined crews accomplished all of the major goals of the mission, which included:

• Installing atop the Destiny module the $600 million S-Zero truss, a 44.2-foot (13.5-meter) long girder packed with computers, navigation systems and the wiring and plumbing needed to eventually distribute power and cooling to the rest of the station.

  Additional truss segments will be added during the next two years until there is a rigid beam stretching longer than a football field and that is able to hold more than an acre of power-generating solar wings and heat-dispelling radiator panels.

• Testing the $190 million Mobile Transporter, the first "railroad" in space that is to be used as a moveable base for the station's Canadarm2. Officials continue to report that initial problems experienced during the tests are easily solved and there is nothing wrong with the hardware.

• Boosting the outpost's orbital altitude by about 6.5 miles (10.5 kilometers).

• Transferring from the shutle to the station several hundred pounds of science experiments and supplies, which included nitrogen and oxygen gas, as well as drinking water.

• Staging four spacewalks to securely attach and wire the truss and transporter to the station's systems.

Earlier Wednesday, before the hatches between Atlantis and the station were closed at 12:04 p.m. EDT (1604 GMT), the ten humans onboard the combined complex -- seven from STS-110 and thee from Expedition Four -- gathered inside the Destiny laboratory to say their farewells and thank the entire government and contractor team who worked on the mission.

"The last week up here at the International Space Station Alpha has just been an incredible experience for everybody," said shuttle skipper Mike Bloomfield. "Alpha is just an incredible place to be."

Bloomfield thanked his crew's hosts and noted that Bursh, Carl Walz and station commander Yuri Onufrienko were in "good shape" and living aboard a station that is a "good ship... in good running order."

Handshakes and warm embraces followed, along with Bloomfield placing a STS-110 mission sticker on a locker wall inside the Unity node -- a spaceflight tradition for all visiting crews.

Atlantis mission specialist Jerry Ross, the first human to make seven spaceflights and NASA's spacewalking record holder, could be seen wiping away tears as the emotional moment played itself out live on NASA TV a little more than two hours before undocking.

With the shuttle crew departed, the Expedition Four crew will attempt to return to a normal, more relaxed schedule for the their final two months in space, but there's still a lot for them to do.

This weekend they will have to get dressed in their Russian spacesuits and momentarily abandon ship as they fly the Soyuz lifeboat from its current docking port on the Zarya space tug to the nearby Pirs port, which is attached to the Zvezda service module. The maneuver is expected to start about 5:10 a.m. EDT (0910 GMT) Saturday.

That will set the stage for launch of a replacement Soyuz lifeboat, which is to be launched from the Baikonur Cosmodrome on April 25 and dock to the station two days later. Included on the taxi crew will be South African space tourist Mark Shuttleworth.

The Expedition Four crew is to return to Earth in June aboard shuttle Endeavour, which is now targeted for launch from Florida no earlier than May 30.