Another problem for astronauts is the difficulty of exchanging information with people on Earth during long flights. There is no delay now in communicating between astronauts and flight headquarters -- known as Mission Control. But messages between Earth and distant planets will take minutes to arrive.
Mental health is another important issue for long space flights. And, because astronauts will be inside their small spaceship together for months, they must work well as a team. There could be problems if one of the astronauts develops personality issues.
?NASA plans to send humans to Mars by 2030. The mission would take about two-and-a-half years. That is almost six times longer than the longest stay in space. One reason NASA extended the life of the International Space Station was to do more medical research on the effects of a longer stay in space.
Starting in 2015, an American astronaut and a Russian cosmonaut are to stay on the space station for one full year. The Russian cosmonaut Valery Polyakov has already stayed longer than a year in space. He worked on the Russian space station Mir in 1994 and 1995.
Scientists say they now have better measuring devices and testing methods. They want to use them to study the changes in the body and mind during long stays in zero gravity. Their research is aimed at learning if such changes in physical condition will remain or will return to normal a few months after they have returned to Earth.
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