With pilot Stephen Frick at the controls, the shuttle Atlantis undocked from the international space station today at 2:31 p.m. as the two spacecraft raced across the North Atlantic Ocean at five miles per second.

"Atlantis, departing," Navy Capt. Daniel Bursch said from inside the lab complex as the shuttle pulled away, ringing a ship's bell in what has become a tradition aboard the outpost.

Frick flew Atlantis through a slow, lap-and-a-quarter loop around of the station before leaving the area for good around 4:15 p.m., ending a week of joint work to attach a huge truss section to the top of the international space station.

"Atlantis, Alpha, Godspeed and happy landings," station engineer Carl Walz radioed from the lab complex as Atlantis began its final departure.

"Hey Carl, Dan, Yury, thanks so much. We've enjoyed the last week with you guys, you've been outstanding hosts," shuttle skipper Michael Bloomfield replied. "We've just been admiring the incredible view you have up here and the machine you live in, Alpha, is really beautiful. So thanks so much for taking care of us the last week, we'll keep you in our thoughts and prayers and we'll see you on the ground in a couple of months. We'll have you over and have a real barbecue party."

"All right, sounds great, we'll bring our kerchiefs."

Atlantis is scheduled to glide back to Earth Friday, landing on runway 15 at the Kennedy Space Center at 12:26:21 p.m. Following a Soyuz taxi flight later this month, the shuttle Endeavour will blast off May 30 on a mission to carry the station's next full-time crew into orbit and to bring Walz and his crewmates - commander Yury Onufrienko and Daniel Bursch - back to Earth. Launch had been targeted for May 31, but it has been moved up one day to provide a bit of cushion between the shuttle and another rocket scheduled for launch a few days later.

Endeavour also will carry a new wrist-roll joint up for the station's robot arm that will be installed during the mission's third and final spacewalk. The new joint is being installed because of an avionics problem in one of the redundant sets of avionics currently in control of the space crane.

Atlantis' crew attached the S0 truss, the first section in a nine-piece beam that eventually will stretch the length of a football field and carry the station's main solar arrays and radiators. A flight scheduled for launch Aug. 22 will carry up the next truss segment, which will attach to the starboard side of S0 and a flight scheduled for launch Oct. 6 will carry up an identical port-side section. Radiator and solar array sections will be added next year.

"For the record at this point, we have now flown 26 missions in support of ISS since the FGB launch in November 1998 and in the last 21 months we've flown 22 flights successfully and that is unprecedented in human spaceflight (history)," said Mike Suffredini, manager of space station integration at the Johnson Space Center. "So we're setting records as we go.

"There's 165 tons on orbit at this time with well over a million lines of (computer software) code, we've conducted 37 EVAs with a total of about 230 hours and yes, we are also doing research in the middle of all this. We've conducted, or are in the process of conducting, 54 investigations with over 70,000 hours of research time. So we're well on our way, we're doing research while we're assembling space station and we believe we're set for the upcoming elements to fly."

By the end of this year," he said, "we'll have over 200 tons on orbit and be we'll on our way with research and be in a posture then for the addition of the rest of the power modules which begin coming up in 2003."

For readers interested in raw detail, launch package manager Ben Sellari provides the following summary of what the Atlantis astronauts accomplished during their mission to attach the S0 solar array truss section to the international space station:

• Installed the S0 element adding 26,716 pounds to the ISS
• Transferred 146 pounds of oxygen (130 pounds required)
• Transferred 45 pounds of nitrogen (40 pounds required)
• Transferred 1,463 pounds of water to ISS.
• Estimated 2228.04 pounds of hardware and supplies delivered to ISS
• Transferred 22.9 pounds of spacewalk hardware to ISS
• Estimated 2450.34 pounds of logistics transferred to shuttle
• Disposed of about 229 pounds of condensate from ISS
• Boosted station altitude by about five nautical miles
• Conducted four spacewalks totaling 28 hours and 22 minutes (single-flight record for ISS assembly)

Here is a list of spacewalk actions during Atlantis' mission:

• Total bolt actuations: 289
• TA clamps employed: 92
• Connectors mated or demated: 159
• Connector caps removed or installed: 49
• PIP pins, actuators or latches cycled: 55
• Circuit interrupt device on-off cycles: 12

The station astronauts, meanwhile, face a hectic schedule over the next few days and weeks. Early Saturday morning, they plan to strap into their Soyuz lifeboat and undock around 5:10 a.m., moving the spacecraft from its current docking port on the Russian Zarya module to a port on the Pirs airlock compartment attached to the Zvezda command module.

That will clear the way for the arrival of a fresh Soyuz lifeboat that's scheduled for launch from the Baikonur Cosmodrome around 2:26 a.m. EDT on April 25. Docking at the station's Zarya port is expected around 4 a.m. on April 27. The so-called "taxi crew" delivering the new Soyuz is made up of commander Yuri Gidzenko, Italian astronaut Roberto Vittori and South African space tourist Mark Shuttleworth. The taxi crew will spend a week aboard the station before undocking around 7:05 p.m. on May 4 and returning to Earth aboard the lab's older Soyuz.