Six men confined together on a virtual return voyage to Mars have celebrated a year in isolation.

The Mars500 project is designed to see if future space explorers can withstand the psychological pressures of a mission to the Red Planet that could last many months.

Having “landed” on a mock Martian surface, they are now heading back to earth in their “spaceship”.

The craft, sited near Moscow, consists of four sealed interconnected cylinders with a total volume of 550 cubic metres.

The Russian, French, Italian and Chinese crew have their own private cabins and work together like astronauts on the International Space Station.

In a letter home, French engineer Romain Charles, 31, wrote: “The dark side of this routine is that every day for the past year we woke up at the same time to do the same medical controls with the same devices: no weekend or holiday breaks for a year!” Crewmate Diego Urbina, 27, from Italy, wrote: “Wow, it’s already been a year. One way to visualise it is if you think of what you were doing exactly one year ago and then picture yourself living in a windowless metal box from then.”

The crew, whose mission began on June 3 last year, “arrived” at Mars at the end of January. After unloading cargo, three of the crew “landed” in a large hall built to look like the Martian surface.

Wearing spacesuits, the explorers collected samples, set up experiments and drove a Martian rover. The trio then “flew” back to the mother-ship to start the long trip back home on March 2.

They are due to end their mission on November 5 this year, when the hatch of the isolation facility will be opened. So far the crew members appear to have coped well, with no sign of the kind of conflicts that bedevil Big Brother housemates.