Inside, the eight men and women who make up the joined shuttle-station crew found a gleaming white science research center that's about as big as the interior of a large business jet.

Coming 17 years after then-U.S. President Ronald Reagan announced plans for the international station, the moment clearly was an ecstatic one for both the astronauts and their cosmonaut colleagues.

They all smiled and snapped pictures of each other. Some began tumbling, twirling and turning flips in weightless outer space. Others celebrated with high-fives, and the Americans all wore red-white-and-blue socks adorned with stars and stripes to mark the occasion.

"The lab looks and feels and smells great, and it looks like all the hard work really paid off," Cockrell told engineers in NASA's space shuttle and space station Mission Control Centers at Johnson Space Center in Houston, Texas.

"We're watching it down here, and it looks awesome," station flight director Sandy Magnus replied. "And we hope you guys enjoy your new room on your new house."

With three pressurized wings already in place, the addition of the expansive Destiny lab made the international station larger in terms of habitable space than NASA's 1970s Skylab complex or the Russian Mir outpost.

Counting it's massive American solar wings and smaller Russian arrays, the new outpost now weighs about 112 tons and measures 171 feet (52 meters) in length, 90 feet (27 meters) in height and 240 feet (73 meters) in width.

The hatch-opening ceremony came a day after Atlantis mission specialist Marsha Ivins berthed the 16-ton lab to the station with the shuttle's Canadian-built robot arm.

Shuttle crewmates Robert Curbeam and Tom Jones gave Ivins a spacewalking assist, routing crucial electrical power cables and coolant lines despite a dangerous leak that exposed Curbeam to toxic ammonia.

The assembly work took about an hour longer than expected - time needed to conduct extensive decontamination procedures to make certain any frozen ammonia crystals on Curbeam's suit wouldn't sublimate when he reentered the shuttle, turning into poisonous gas.

The lengthy suit decontamination, meanwhile, put the joined crews behind schedule on the time-critical activation of crucial lab computer, cooling and electric power systems.

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But all that work largely had been carried out by the time Cockrell and Shepherd gathered their crewmates in front of the doorway to Destiny.

"It's been a lot of hard work on thousands of peoples' parts, and a long number of years getting ready to bring the Destiny lab to the International Space Station," Cockrell said.

"It's finally here. It's gone through a lot of wickets. We've gone through a lot of effort to get it attached, and now we'd like to turn it over to 'Shep' so that he and his crew - and subsequent crews - can begin the process of scientific research and better living in space."

Then in true NASA fashion, Cockrell had Shepherd autograph the so-called "DD 250" - an official U.S. government document signed by the agency when it took possession of the lab from its prime station contractor, The Boeing Co.

"Shep, before we hand it over to you, we have a little paperwork for you," Cockrell said as a crewmate floated the document over to the station skipper.

Then, providing color commentary as Shepherd made his mark, Cockrell turned to onboard cameras and said: "Shep is signing it in the spot that says 'received by.'"

The six astronauts and two cosmonauts then donned what Cockrell called "very classy" eye goggles - a precaution in case any airborne particulate or fine debris had shaken loose during the lab's launch from Kennedy Space Center.

The atmosphere inside the lab, however, was pristine, and the safety glasses - sporty as they looked - were quickly ditched.

"We do not see anything floating free in here. It's completely debris empty, so we are going to take off our goggles," Cockrell said.

"Copy that," Magnus replied.

The orbital ceremony - and the cavorting that followed - was capped relatively quickly, and the joined crews turned their attention to lab outfitting work that had been deferred due to the decontamination procedures that sent Saturday's spacewalk into overtime.

Floating side by side, the eight frontier pioneers began working on systems that will transform Destiny into the nerve center of the station, enabling command and control functions for the entire outpost to be carried out from within it.

Laptop computers that will control key life support systems - such as those used to generate oxygen, purify water and remove carbon dioxide and humidity - were set up along with data handling, video switching and audio communications equipment.

Once completed later this week, the outfitting work will set the stage for the first of 13 science research facilities to be launched up to the station March 8 aboard shuttle Discovery, which will ferry a fresh crew to the outpost and taxi Shepherd and his crew back home.

The refrigerator-sized racks - which will be added to Destiny over the next several years - ultimately will house experiments in a wide variety of scientific disciplines, including fundamental physics, biology, chemistry, ecology, Earth science and space science.

Medical studies on Destiny also are expected to help researchers develop countermeasures for treating the ill effects of long-term spaceflight on the human body, data deemed critical to preparing for human expeditions to Mars and beyond.

That biomedical work will be enabled by the science rack to be flown on Discovery, which will roll onto its seaside launch pad Monday at about the same time Curbeam and Jones venture outside Atlantis for the second of their three planned spacewalks.

With a planned start time at 10:13 a.m. EST (15:13 GMT), the two spacewalkers aim to move a stowed shuttle docking port to the forward end of the Destiny, where it will serve as a parking place for future station construction crews.

Curbeam and Jones are scheduled to head out on a third and final spacewalk about 10:18 a.m. EST (15:18 GMT) Wednesday. The prime job at hand: Stowing a spare communications antenna outside the international outpost.

Atlantis is scheduled to depart the station Friday after a final farewell and hatch-closing ceremony now scheduled for 7:18 a.m. EST (12:18 GMT) that day. The shuttle and its crew are due to land at Kennedy Space Center at 12:52 p.m. EST (17:52 GMT) Sunday, Feb. 18.

Shepherd and his crew - which includes Russian cosmonauts Yuri Gidzenko and Sergei Krikalev - are to touch down on terra firma March 20 here at NASA's Florida spaceport.