For the past eighteen months, half a dozen people have been trapped in a tin can in Siberia simulating a trip to Mars, with a simulated landing a couple of weeks ago, followed by two weeks of simulated Martian surface missions, collecting rocks, looking for life, etc.
Or have they?
Rumours are beginning to circulate that the simulation is a massive conspiracy and that the astronauts have actually gone to Mars.
"They've made a big thing about the Mars 500 simulation dome," said conspiracy nut, Colin Piracy, not his real name, as with his real name, they will find him. "Nobody is allowed in it, and there are no windows. They say it's so the astronauts cannot see out, but it's really to stop people looking in and seeing it's empty."
The conspiracy theorists claim that the whole project has been too realistic.
"The duration before the Mars Walk was exactly right, there were radio delays that were microsecond perfect," said Piracy. "They never showed the astronauts moving around during their zero-g part. They dared not, because they would have floated and it would have given the game away."
Now the astronauts are moving around on the surface of Mars, and Piracy sees even more evidence that the whole simulation is a fake.
"The way that they move, that's got to be less gravity than you get on Earth," said Piracy. "They put this flag up and the shadow's so weak, and the flag barely moves."
Piracy has also noticed that there are two tracks of light at night. "Two moons, you see," he said. "That's just the sort of detail you wouldn't bother with in a simulation."
The joint Russian, European and Chinese effort have all clamoured that the simulation is just that, a simulation, a very accurate simulation, but unreal nevertheless.
"We thank Colin for his statements about the believability of our simulation," said Honn Tzu Martz, the Chinese project designer. "However, he is wrong. I'm sure the astronauts will have a laugh about it when they get back. Outside. Back outside…"