Dr. Vladimir Pletser checks the growth of radishes and alfalfa sprouts during an experiment to determine whether plants can be grown to support a Mars colony during his two-week stay at the Mars Desert Research Station in Utah. Photo Credit: Jan Osburg / University of Stuttgart, Germany

Powerful body, military-style crewcut, easy grin, team player. And then he's got that inner something -a certain confidence and poise brought by years of experience.

Others must have seen it, too.

Which is one of the reasons he is an astronaut candidate for Belgium's space program and, since 1985, a staff member of the European Space Agency. He is also one of the crew members spending two weeks at the Mars Desert Research Station, a project sponsored by the Mars Society, which promotes exploration of the Red Planet.

Would he go live on Mars if the trip were offered?

"I'll be signing immediately, signing with both hands, both feet,'' said Dr. Pletser, 46. "Yes, I'll be gone, sure. Even if we do not return. A one-way ticket would be fine for me.''

Although Dr. Pletser has not yet been to space, his experiments have - he has degrees in mechanical engineering and physics, with a doctorate in astrophysics.

One of his experiments flew on a Space Shuttle mission in 1998 with John Glenn Jr., the first American astronaut to orbit the Earth.

Another experiment is set for the International Space Station in a few years.

Dr. Pletser floats upside down in an Airbus cabin during the weightless portion of a parabolic flight in October 2001. Dr. Pletser is a member of the crew at the Mars Desert Research Station near Hanksville, Utah. Photo Credit: European Space Agency

As manager of the European Space Agency's aircraft parabolic flight program, he flies on specially equipped airplanes that duplicate zero gravity when they go into free fall during a roller-coaster type of maneuver.

The pilot puts the aircraft into a steep climb, creating twice the force of gravity on its occupants, and then cuts the engine. As the aircraft falls to Earth, a weightless condition is created for about 20 seconds, which is used for astronaut training and scientific experiments in microgravity. Then the pilot pulls the aircraft out of its steep, 45-degree dive, again making passengers feel as if they weighed twice as much as they really do.

Dr. Pletser has done this 3,250 times, accumulating more than 18 hours of weightless experience.

Newcomers are advised to take it easy on their first flight because of the severe stress on the body. Dr. Pletser advises them to lie on their backs while experiencing twice Earth's gravity for the first time. If all goes well, they can try sitting up the next time.

During the weightless condition, first-timers tend to react instinctively - which is the wrong thing to do.

"With zero G, you notice the newcomer because they start to swim," Dr. Pletser said. "The reaction is that you want to propel yourself, and your reflexes react like in water.

"Of course, it's totally different because of kinetics and the viscosity of air. So you can flap your arms and kick your legs - it would not help at all, except maybe to hit someone."

Nausea is also common for about half of those who experience zero gravity because of motion sickness, Dr. Pletser said. Fortunately, he is immune.

But no one escapes the physical demands of the maneuvers, which put a severe strain on the heart, muscles and skeleton. During a standard 2 ½ hour flight, there are 30 parabolas producing a total of 10 minutes of weightlessness. Usually there are three such flights during a one-week campaign, normally Tuesday through Thursday.

"After a certain number of parabolas, you're exhausted," Dr. Pletser said. "You want to crash out in the afternoon or evening. On Thursday, you're totally liquefied."

The flights are necessary, however, to train astronauts and test equipment before being sent into space, even for a short period.

"There's no need to go to space for some experiments,'' Dr. Pletser said. "If you're well-prepared and your experiment is well-designed and well-conceived, 20 seconds is all the time in the world that you need."

He has flown these missions with the National Aeronautics and Space Administration, the Russian space program and the 15-nation European Space Agency.

His current experiment, which would fly into space in 2004 or 2005, is what he calls a Protein Crystallization Diagnostic Facility. The experiment exploits the fact that, during weightless conditions, it is possible to build protein molecules with very large crystalline structures that is not possible otherwise. That makes it easier to analyze them on Earth with an X-ray diffraction machine, and determine the three-dimensional structure of the molecule. Then it's possible to predict how they would interact with other molecules.

"Basically, this is the idea of developing new medication, new molecules for pharmaceutical purposes, to fight infections and viruses," Dr. Pletser said. "It's basic research that we do as a first step toward applied research later on, that will benefit mankind on Earth."

Although NASA may dominate space headlines in the United States, the Russians have held the world record for the number of satellites in space since Sputnik was launched in 1957, he said.

And the European Space Agency has played a vital role, too, helping build part of the Hubble space telescope. In 1983, one of agency's astronauts, Ulf Merbold of Germany, was the first non-American to fly on a Space Shuttle mission. Another astronaut, Jean-Pierre Haignere of France, spent more than six months on the Russian space station MIR, the longest flight ever performed by a non-Russian astronaut.

And the agency's Automated Transfer Vehicle, boosted into space by the Ariane 5 heavy-lift launcher, is expected to help keep the football-field-sized International Space Station from falling from orbit during its lifetime. All of these missions by the European Space Agency would launch from the Guiana Space Center in Kourou, French Guiana.

So far, Dr. Pletser has been nominated but not yet accepted as an astronaut. Still, he remains optimistic.

"For the moment, I am still waiting, expecting to one day fly to the Space Station,'' he said. "I still have hope. When I see, for example, people like John Glenn flew at 77, there's no age limit.

"Shuttle commanders typically are in their late 50s, between 50 and 60. So you have a lot of experience, but still you're fit and you pass the medical.''

For the Mars Society, Dr. Pletser has conducted experiments at Devon Island in the Arctic to determine whether it would be possible to detect underground water on Mars using seismic shock waves, much like oil exploration on Earth.

His current mission at the Mars Desert Research Station will help determine if it is feasible to grow food in a greenhouse on Mars.

And then someday, for Dr. Pletser, it's on to Mars.