The car-park cosmonauts come back to Earth (without a bump)

Hours to go for crew who have spent 17 months simulating mission to Mars

About lunchtime tomorrow, six men will emerge, bleary-eyed, from a "spaceship" in northern Moscow, to see daylight and the real world for the first time since they were locked away in the mock-up craft on a roasting hot day in June last year.

The multinational crew of "terranauts" has spent the past 17 months simulating a manned space mission to Mars, in a stationary experiment designed to test the physical and psychological effects of a journey to the Red Planet.

In the experiment, run by a Russian research centre in co-operation with the European Space Agency, six carefully selected volunteers were locked in a model spacecraft for 520 days.

The all-male crew of six come from a variety of backgrounds, with three Russians joined by one Earth-bound astronaut each from Italy, France and China. "I would say the guys have a very positive mood," Mark Belanovsky, the project's deputy director, told AFP yesterday. "They know that they have done something really big."

During the final stretch of the experiment, the crew are experiencing a "spiral trajectory towards the Earth's field of gravity". But the experiment has not been able to simulate the weightlessness that would accompany a real mission to Mars.

There has been plenty of scoffing at the project, given its Earth-bound nature, but the organisers insist that the experiments will really help in the planning of a future manned visit to Mars, which realistically is still at least 20 years away. For 17 months, the participants have had their brains and bodies monitored, performed tests, and had no contact with anyone else.

They emerged from the spaceship only briefly, in the middle of the mission, to take an incredibly modest step for mankind, and walk around a small sandy area meant to represent the surface of Mars. They have only been able to eat special astronaut food, and computer-based communication with the mission's "control room" has been subject to a delay.

There were fears when the experiment started that, faced with such a long time together in such a confined space, tension or even physical fights could break out. A previous, shorter experiment had to be halted after a female Canadian participant said she was forcibly kissed by one of the Russian male participants and a fist fight broke out among the crew.

Organisers said that this experiment had been made male-only to reduce tension. As the mission entered the home straight in August, there was a brief period of flared tempers, but this was swiftly overcome, say the participants. A recent video from inside the capsule shows the crew, all apparently in good spirits, discussing which experiments they have enjoyed the most and which the least during their long stint inside.

Tomorrow will not quite be the end of the ordeal for the six. Now they will be put in quarantine for four days, when they will undergo intensive medical tests and psychological evaluation. They can speak to the media and be reunited with their families on Tuesday, but remain in Moscow for a further month for tests.

Voyage to Mars: The risks

Bones Real space travellers experience a loss of calcium and phosphorus as the Earth's gravitational pull is removed. It is believed that as much as 3.2 per cent of the body's bone calcium and phosphorus are excreted in urine and faeces during space flight.

Radiation exposure Unlike, the "car-park cosmonauts", real space travellers are exposed to space radiation, which is normally shielded from Earth. Exposure to high levels of radiation increases the risk of cancer and other diseases.

Immune system The immune system is also adversely affected by prolonged periods in space. Gravity is thought to change the shape of red blood cells, and eventually to lead to a loss of plasma and red blood mass.

Muscle wastage Even experimental astronauts share the complaint about muscle wastage through lack of exercise.