Tribune photo by GREG FIGHT

CAPE CANAVERAL—Capping a successful 13-day mission to the International Space Station, the crew of Atlantis glided home to a postcard touchdown at 9:07 a.m. today, setting the stage for another shuttle venture in less than three weeks.

NASA’s commitment to a Florida landing on the first attempt was a no-brainer, as ideal weather around Kennedy Space Center made the powerless descent from orbit routine. The agency had extra motivation to bring Atlantis home: The Pentagon is eager to shoot down a crippled spy satellite in low-Earth orbit, and nobody wanted a space shuttle to get hit with debris.

Atlantis announced its arrival with a pair of sonic booms that scared thousands of birds around the compound. The year’s first shuttle mission—originally scheduled for December—put the agency on track for Endeavour and Discovery missions in March and April and then three more beginning in the fall.

The astronauts aboard Atlantis delivered the $2 billion Columbus laboratory to the station, bringing the giant orbiting platform to more than 60 percent of its completion. Columbus is the first major part of the station to be operated by members of the European Space Agency and a team of more than 500 scientists.

Some of those scientists paid careful attention to an astronaut on the latest mission. Hans Schlegel of Germany became sick shortly after Atlantis blasted off, and NASA called his condition a “private medical matter.” However, Schlegel’s illness forced the crew to delay a critical spacewalk at the station and extend the mission by a day.

The unexpected problem underscores how even highly trained astronauts can quickly succumb to the disorienting rigors of space. The abrupt change from gravity to weightlessness can throw off an astronaut’s body in more ways than an upset stomach or nausea – it can disrupt the body on the molecular level, said Shenda Baker, a professor of chemistry at Harvey Mudd College in Claremont, Calif.

Baker is studying how immune cells adjust to space travel, and one of her experiments flew on a shuttle mission last year.

“What we have found is these immune cells act like they’re stressed, and they produce chemicals that react to your body being ‘attacked’ in microgravity,” Baker said by telephone. “By not being influenced by gravity, these cells feel stressed.”

Although scientists need to do more research on the long-term effects of immune cell stress in space, Baker says the current findings point to more than the temporary sickness Schlegel may have felt. If an astronaut’s immune cells are compromised on a mission, would it complicate an injury or infection?

The cells in question are called monocytes, white blood cells formed in the bone marrow that destroy bacteria. When a person is cut or infected, an army of monocytes jumps into action to defend the body.

In the absence of gravity, these monocytes appear to lose their sense of balance, Baker said, and aren’t sure where to do battle.

“Human cells don’t like not knowing which way is up,” she said. “We think of a cell as uniform and not caring which way is up. But without gravity, they feel stressed.”

Making matters worse, infections thrive in a weightless environment, Baker said. “Bacteria love microgravity. It proliferates and often becomes even more virulent.”

Baker will continue her research by comparing more “cellular expression” experiments done in orbit with identical ones in the lab on the ground. Results could reveal clues about how injuries, wounds and infections respond during long-term space missions and how doctors can better prepare astronauts for unexpected health problems.

With Atlantis safely home, NASA is preparing for Endeavour’s 16-day mission to deliver a Japanese science lab to the station, set for launch at 2:30 a.m. March 11. It will mark the 25th shuttle mission to the station.