Image credit: Oleg Voloshin/AP

Three Russians, a Frenchman, an Italian-Colombian and a Chinese walk out of a set of windowless steel modules in Moscow after 520 days.  No, it’s not the beginning of a bizarre joke, it’s the end of the longest simulated space flight in history.

The mock mission to Mars, which was completed today, was intended to see how humans would hold up, both physically and psychologically, during the stresses of a long space flight.

The modules the researchers were housed in received neither daylight nor fresh air, and psychologists were interested to observe what types of conflicts would erupt over the more than 17 months.

While the experiment could not simulate weightlessness or the hazards of space radiation, the crew did enact a  Mars landing. Crew members ressed in space suits and left their cramped quarters to plant the flags of Russia, China and the European Space Agency in a sand-covered room.

All the men emerged from the mission healthy and did not appear stressed out, but they will spend three days in quarantine to reduce the risk of illness. Psychologists said in many ways the mock mission was tougher than an actual mission  because the crew did not experience the joys and dangers of  taking flight.

“On the Mars 500 mission, we have achieved on Earth the longest space voyage ever so that humankind can one day greet a new dawn on the surface of a distant, but reachable, plant,” said European Space Agency participant Diego Urbina, according to the BBC.

A real manned mission to Mars is not expected until the 2030s.

The Associated Press contributed to this report.