When astronauts travel to the International Space Station, the journey takes about two days and the usual tour aboard the orbiting outpost is six months or less.
No one has ever spent a year on the space station in a single mission, but that is going to change.
A Russian cosmonaut and an American astronaut are going to spend a year aboard the space lab to learn more about the way humans react to extended stays in space.
A Year in Orbit
Julie Robinson, a scientist at NASA's Johnson Space Center in Houston, Texas, said mission is designed to collect information needed to send people to new destinations in the solar system.
"Today, we're in a position where we think we know a lot more about what it takes to keep a crew member healthy for six months in orbit," said Robinson. "But we know that for a variety of space missions that are under consideration, we really might need crew members to go a little bit longer."
NASA said only four people have spent a year or longer in orbit on a single mission - all on them aboard Mir, the Russian space station that eventually fell back to Earth in 2001. The record-holder is a former Russian cosmonaut, Valery Polyakov, who spent 438 days in space - from January 1994 to March 1995.
NASA's Julie Robinson said there is much to be gained from an extended stay aboard the International Space Station.
"In the past, the Russian cosmonauts that have flown for one year, they flew at a time when both medical technology was not as advanced as it is today and also when we didn't have the knowledge that we've gotten from the space station so far about exercise routines and nutrition," said Robinson.
Living in Microgravity
People have been aboard the space station continuously for the past 12 years, and astronauts serve as researchers and research subjects. They must deal with microgravity, an environment where the pull of gravity is weak and things seem weightless. Scientists have studied the effects of microgravity on muscle mass, strength, vision and bone density.
Scientist Julie Robinson said one of the goals of this longer mission is to learn whether physiological changes plateau or continue as people spend more time in space.
Staying Strong in Space
Scott Smith, a NASA scientist who specializes in nutrition at the Johnson Space Center, said recent studies show that crew members who eat well, consume enough Vitamin D and exercise vigorously can maintain strong bones.
"We have shown, for the first time in 51 years of human spaceflight, significant progress in maintaining bone mineral density," said Smith. "Again, there are some things that we still need to do in terms of understanding changes in bone strength. There are some things we need to do in terms of optimizing exercise, in terms of optimizing nutrition. But again, the fact that we're making progress in human subjects during spaceflight is very exciting stuff."
The yet to be named astronaut and cosmonaut are expected to take a Russian Soyuz spacecraft to the International Space Station in 2015 to begin their year in orbit.