Russian space researchers will lock six men in a metal tube for more than year in an effort to mimic the stresses and challenges of a manned mission to Mars.

The 500 Days experiment, under development by the Russian Institute of Medical and Biological Problems, will isolate human volunteers in a mock space station module for  -- as its namesake suggests -- a complete 500 days to study how a long mission to Mars might affect its human crew.

"Obviously, we're very interested in the results," NASA spokeswoman Dolores Beasley said of the long-duration study during a telephone interview. "It is a high priority for us."

During the 500 Days study, six volunteers will depend on a preset limit of supplies, including about 5 tons of food and oxygen and 3 tons of water. A doctor will accompany volunteers inside the module to treat illnesses and injuries. Volunteers will only be allowed to quit the experiment if the develop a severe ailment of psychological stress.

But experiment participation is not solely reserved for Russian volunteers, institute officials added.

"We have informed our American colleagues that we plan to start an imitation of a manned flight to Mars with the help of volunteers in 2006," Yevgeny Ilyin, deputy director for science at the institute, told Russia's Interfax news agency during a recent Russian-American working group meeting in Moscow.

NASA has been invited by Russian scientists to join in on the Mars mock mission, but a final decision by the U.S. space agency is pending, said NASA's Guy Fogleman, NASA director of the Office of Biological and Physical Research's Bioastronautics Research Division, to Russian reporters.

The space agency has not yet decided whether it will participate, though a decision is anticipated some time in the next few months, Beasley added.

NASA astronauts currently serve six-month missions aboard the International Space Station (ISS), though Russian flight controllers have lobbied to increase joint U.S.-Russian missions up to one-year in duration.

"Any medical and biological experiments made on board the International Space Station aim at long-distance space flights of the future," Ilyin said.

The U.S. single spaceflight endurance record falls on the crew of ISS Expedition 4, Carl Walz and Dan Bursch, who lived aboard the space station for a total of 196 days.

Veteran Russian cosmonaut Valery Polyakov, a medical doctor, set the current world record for the longest continuous spaceflight when he spent about 438 aboard Russia's Mir space station between 1994 and 1995.

Polyakov told Interfax reporters that the 500 Days experiment will not include female volunteers.