Russian scientists are selecting volunteers to be locked in a capsule for 500 days to test plans for a trip to Mars.
Russia last tried to send an orbiter probe to Mars in 1996
The mock mission is designed to simulate the tough conditions of a space trip to the Red Planet.
A team of six men will be physically cut off from the outside world to test equipment intended to make them self-sufficient for long periods.
Their capsule will consist of a bedroom, a kitchen and a laboratory.
The capsule's own equipment should make all of the oxygen they need, repeatedly recycle three tonnes of water and grow some food to add to five tonnes of supplies packed inside.
The experiment, to be based in Moscow, tests a plan to make long-range space travel and settlements possible.
But such a real Mars mission is not going to happen any time soon.
Scientists only have two of their six volunteers so far and will not begin the mock-up mission until some time in 2006.
Russia holds several space records, including the record for the longest amount of time spent in space.
That honour goes to cosmonaut Valery Polyakov, who lived on the Mir space station for 438 days in 1994-1995.
Scientists are concerned about the effects on the human body of such lengthy periods in space.
Muscle waste, bone formation, changes in the immune system and psychological wellbeing are some of the areas being researched.
Various space agencies are also conducting experiments designed to simulate conditions in space.
A series of bed-rest studies were carried out in 2001 by the European, French and Japanese space agencies.
These involved volunteers lying on a bed with the head of the bed tilted six degrees below horizontal for a period of 90 days, to replicate weightlessness.
The European Space Agency in October repeated a call for female volunteers to participate in a 60-day bed-rest study planned for next February.
Russia's most recent solo project to Mars was the Mars 96 Orbiter, launched in 1996.
The spacecraft failed to achieve orbit around the Red Planet and in November the same year, re-entered the Earth's atmosphere and crashed.