"We were just trying to be theatrical here."

Along with the placement of her custom-made lifeboat seat-liner, the flightsuit "fit-check" capped the first of an estimated 45 "crew exchanges" that are expected to take place at the station over the next 15 years.

It also marked the beginning of a long-anticipated four-and-a-half-month adventure that calls for Helms and the so-called Expedition Two crew to start up scientific research on the station while overseeing further outpost construction work.

Said Helms: "We are just going to have the time of our lives."

Launch last Thursday aboard Discovery, Helms and her crewmates are replacing the stations three inaugural tenants: U.S. astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev.

Discoverys flight to the station was an encore of sorts for the three members of the relief crew, who got an early look at the outpost during a maintenance mission last May.

Then fledgling, the station since has doubled in size. It now features Russian crew quarters as large as a city bus, massive American solar panels that have a wingspan greater than that of a 747 jumbo jet, and the expansive U.S. Destiny science laboratory.

The enormous growth was particularly striking when Helms and her crewmates pulled into the station last Saturday.

"When we came up to the space station last time, of course my impression was that it was absolutely huge. And this time when we came up it was twice as large as it was nine or 10 months ago," Helms said. "I have to admit that once we got the solar panels out there on the American segment, its just turned into a giant flying vehicle. And it looks absolutely surreal."

In training for their expedition for four years, Helms, Voss and Usachev have formed a tight bond that is expected to serve them well during their long stay at the isolated station.

"Were more like a family than we are a crew," said Helms.

Added Voss: "We just seem to mesh together very well, and I expect us to get along greatly during the four and a half months well be up here and get a lot of work done."

The final stage of the crew swap took place as the astronauts and cosmonauts aboard the joined shuttle-station complex hustled to unpack an Italian moving van that was temporarily mounted to the station Monday.

The Leonardo cargo carrier was launched with five tons of supplies and equipment, including the stations first science research package.

That refrigerator-sized rack of biomedical experiment apparatus was moved into the Destiny lab Tuesday, heralding the start-up of research that could lead to future human expeditions into the solar system.

NASA lead space station flight director Rick LaBrode called the move "a tremendous milestone."

"Its really what were building this International Space Station for -- to do science operations, and hopefully improve life on Earth, and give us hopefully means for even longer-duration space travel to Mars and beyond," he said.

The Expedition Two crew will carry out a suite of biomedical experiments during its station expedition, which will get an official start when hatches between the shuttle and the station swing shut a few hours before Discoverys scheduled departure on Saturday.

Outgoing station skipper Shepherd will officially hand over command of the station to Usachev during a farewell ceremony at 8:12 p.m. EST Saturday (01:12 GMT Sunday).

Shepherd and his two Russian colleagues will taxi back to Earth aboard Discovery next Tuesday, capping a 140-day stay in space.