AP AEROSPACE WRITER

Marcia Dunn

CAPE CANAVERAL, Fla. (AP)—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. They’ll share the shuttle with the most rats ever carried on a shuttle.

The launch is scheduled for Thursday morning.

‘‘All kidding aside, we’re just tickled to death to have the opportunity to sort of earn our tickets, if you will, and really contribute something meaningful,’‘ said astronaut William McArthur Jr., an Army officer and former test pilot.

‘‘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.

NASA program scientist Frank Sulzman says the shuttle work will complement studies already conducted on Mir.

‘‘The experiments that we are conducting on this mission are things the Russians have not been able to do because of the way their program is designed,’‘ he said.

For instance, Sulzman said, it’s difficult for Mir cosmonauts to bring back biological samples and to collect medical data during the first few days of space flight—a critical time in the body’s adaptation to weightlessness.

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.

‘‘Whether or not it’s significant to our performance, whether it is dangerous to our health, that’s yet to be determined. We don’t think so,’‘ said astronaut-physician M. Rhea Seddon, Columbia’s payload commander.

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. There were just 29 rats on that flight and no rat handling; Seddon was on that crew, too.

On this trip, Seddon, Fettman and the two other scientists will insert tiny catheters into the rats’ tail veins to draw blood and inject hormones and radioactive isotopes, and collect rat droppings to measure calcium content.

They also will dissect five or six of the rats and preserve their tissue for postflight study. The remaining rodents will be killed and dissected after the mission, the customary fate of shuttle-flying rats.

Biologists say the only way to determine the effects of weightlessness is to kill some of the animals in space rather than wait until they’re back on the ground and re-exposed to gravity.