After nearly eight months' journey in a small, enclosed craft, the crew of the Mars500 mission is nearing the turning point of its voyage—arrival and disembarking at the Red Planet. They will spend 10 days there, exploring the surface in a series of excursions, before returning to their craft and beginning the lengthy trip home.

At no point in any of this exploration, however, will the six-member Mars500 crew actually leave the surface of Earth. The entire mission is a simulation, housed in a series of capsules at Russia's Institute for Biomedical Problems in association with the European Space Agency. But the isolation and cramped confinement of the mission are real, even if the journey itself is not.

The Mars500 program is a test meant to simulate some of the mental and physiological effects that a real Mars crew would have to endure on a long journey in close quarters. (Other physical hazards, such as dangerous levels of radiation and the atrophying effects of weightlessness, would also be in play in a real Mars mission.) The six men—three from Russia and one each from China, Italy and France—entered the 550-cubic-meter facility in June 2010, and the plan is to keep them there until the end of the simulated Mars round-trip in November 2011.

On February 12 three of the crew will "arrive" at Mars in their landing module while the other three remain in the main spacecraft. On February 14 they will begin to explore the simulated Martian surface [brown enclosure in diagram above], a 1,200-cubic-meter chamber in which the crew will wear spacesuits. For added realism all communications with mission control will endure an artificial 20-minute delay to mimic the light-travel time between Mars and Earth.

Mars500 is not, of course, the first experiment to lock a number of human participants inside a closed facility. The mission builds on a 105-day pilot project that wrapped up at the Institute for Biomedical Problems in 2009. And, back in the 1990s, there was Biosphere 2 in Arizona. Intended to be a self-contained ecological system, Biosphere 2 was beset first by low oxygen levels and pest infestation and then by managerial infighting. The science never outpaced the project's bad press, and the building is now a research station of the University of Arizona.

Diagram of the Mars500 enclosure: IBMP