Columbia Countdown Started for Longest Shuttle Flight Yet : Space: If all goes as planned, the mission will exceed the current record by five hours. Seven astronauts will study effects of long space travel.

When Columbia lifts off on a two-week research mission, the longest space shuttle flight yet, it will be loaded with seven human guinea pigs and 48 rats.

The seven astronauts will spin in chairs, do bungee jumps, draw blood and conduct other medical tests to study the effects of long space trips.

The launch is scheduled for Thursday morning. The countdown began at midnight Sunday.

“This is my big shot at doing the very best for science that I can,” said Dr. Martin Fettman, a veterinarian and pathology professor at Colorado State University.

If all goes as planned, the mission will exceed by five hours the current shuttle record of 13 days, 19 hours and 30 minutes, set by Columbia last year.

That pales in comparison to NASA’s space endurance record--an 84-day Skylab mission by three astronauts in 1973-74--and Russia’s 366-day Mir space station stay by two cosmonauts in 1987-88.

Space travel is rough on the body over time.

Muscles shrivel, bones weaken, red blood cells dwindle, the immune system diminishes and, for two-thirds of all astronauts, motion sickness strikes.

And space voyagers sometimes feel lightheaded when they return to Earth and try to stand, and their reflexes are slow.

Many of Columbia’s 14 laboratory experiments--eight on humans and six on rats--follow up on work done in 1991 on NASA’s first and only other mission devoted to biomedical research.