New space station crew moves aboard

New Alpha crewmembers Mikhail Tyurin, left, Frank Culbertson, center, and Vladimir Dezhurov

JOHNSON SPACE CENTER, Texas (CNN) -- The new space station crew moved into Alpha Monday, relieving the cosmonaut and two U.S. astronauts who have been living and working on the station since March.

Space shuttle Discovery docked with the orbiting outpost Sunday afternoon, bringing up the new crew: U.S. commander Frank Culbertson and Russian flight engineers Vladimir Dezhurov and Mikhail Tyurin.

They are expected to live on Alpha until December, replacing Russian cosmonaut Yury Usachev and U.S. astronauts Jim Voss and Susan Helms.

Culbertson, Dezhurov and Tyurin officially became residents of Alpha at 3:15 p.m. EDT after their custom-made seat liners for the Soyuz escape module were installed and tested.

"We've completed the transfer into the Soyuz and the leak checks," Culbertson told Mission Control.

The seat liners are key because the escape module -- if needed -- would land on the ground and the seats need to fit precisely to properly protect a returning astronaut or cosmonaut, according to Mark Ferring, the flight director for Alpha.

"The Soyuz lands on the ground," said Ferring. "The acceleration force at the point of impact could be quite severe and these suits are designed to be able to absorb that impact."

Usachev, Voss and Helms, having completed 156 days on Alpha, now become members of the space shuttle crew.

Fresh food, clothes and gear

The Leonardo module hangs from the shuttle's robot arm on Monday.

The shuttle also is delivering food, clothes for the new crew, experiments and equipment. Many of the supplies are stowed in the Italian-built Leonardo multi-purpose logistics module, a giant shipping crate carried to orbit in the shuttle's cargo bay.

Early Monday, Discovery mission specialist Patrick Forrester used the shuttle's robot arm to lift the module from the cargo bay. The module later was bolted to the exterior of the space station's Unity node. The crew opened the hatch on Leonardo and began unloading it. Once empty, the module will be packed with trash and used equipment, returned to Discovery and carried back to Earth.

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The shuttle also is delivering a bedroom suite that will be installed in the orbiting outpost's Destiny science laboratory. Currently, there are sleeping quarters for only two Alpha inhabitants. The third must settle for a makeshift bunk in Destiny.

Germs in space

Discovery's scientific cargo includes about 20 U.S. and Russian experiments, including the first experiment to be mounted to the exterior of the station. More than 1,500 materials samples will remain outside, enduring punishing levels of solar radiation with no protection.

"The kind of things we're looking at, for example, are materials that provide radiation shielding that would be used on space missions, including manned ones to Mars," said William Kinard, a NASA scientist at the Langley Research Center managing the experiments.

Current Alpha crewmembers Susan Helms, left, Yury Usachev, center, and Jim Voss

The hapless subjects include plastics, mirrors, composites and living specimens like seeds, spores and bacteria. They are being checked for their space worthiness to better prepare for future explorations in space.

What kind of risk do the microbes pose to the space travelers?

"None whatsoever. The biological specimens are sealed with multiple seals inside containers. And the viruses that are being flown present absolutely no hazard to the crew," Kinard said.

The shuttle is scheduled to return to Florida on August 22.