Simulated Mars mission 'lands' back on Earth
Six men locked away in steel tubes for a year-and-a-half to simulate a mission to Mars have emerged from isolation.
The Mars500 project, undertaken at a Moscow institute, was intended to find out how the human mind and body would cope on a long-duration spaceflight.
It is a venture that has fascinated all who have followed it around the globe.
The study even saw three of the men carry out a pretend landing on Mars, donning real spacesuits and walking across an enclosed sandy yard.
"It's really great to see you all again - rather overwhelming," said European Space Agency (Esa) participant Diego Urbina after stepping through the opened hatch of the Mars500 "spaceship".
"On the Mars500 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, planet."
The rest of the crew - Russians Alexey Sitev, Alexandr Smoleevskiy and Sukhrob Kamolov, European Romain Charles and Chinese national Wang Yue - smiled and waved to family members who had come to greet them at the Institute of Biomedical Problems (IMBP).
The crew has now been taken away into quarantine for medical checks.
"The international crew has completed the 520-day mission," Commander Alexey Sitev reported to gathered officials.
"The programme has been fully carried out. All the crew members are in good health. We are now ready for further tests."
For much of the Mars500 project, the six had only limited contact with the outside world. Their spaceship had no windows, and the protocols demanded their communications endured a similar time lag to that encountered by real messages as they travel the vast distance between Earth and Mars.
At its maximum, the round travel time for a question to be sent and for an answer to be received was about 25 minutes.
This meant having to resort to text media, such as email and Twitter, and video blogs.
Asked before he came out what he was most looking forward to, Italian-Colombian Mr Urbina told BBC News via Twitter: "Meeting my family, calling my friends, bumping into strangers, going to the beach."
There were many aspects of a real mission that could not be simulated in a Moscow suburb, of course - such as weightlessness and the dangers associated with space radiation.
But scientists have expressed great satisfaction with the data that has been acquired, and are looking forward to applying the lessons learned to ever more realistic scenarios.
During the 17-plus-months of their virtual voyage, the crew took part in various studies to assess the effect their isolation was having on their psychological and physiological well being.
Their stress and hormone levels were monitored, as were their sleep patterns, and their moods. The men also carried out an assessment of the benefits of dietary supplements in such situations.
"I can only praise the crew for their courage and their great spirit," said Dr Martin Zell from the European Space Agency, which was a major sponsor on the project.
"They were a brilliant team - they really will finish as a crew and not six individuals," he told BBC News.
Tentative discussions have now begun between the partners on the International Space Station (ISS) about the possibility of doing some sort of isolation experiment in orbit.
Initially, this might simply involve introducing a delay in communications to controllers in Moscow and Houston, US. Ultimately, it could also involve removing crew members into separate modules to give them a taste of what the Mars500 participants have gone through.
Certainly, the partners want the ISS to become more of an "exploration testbed" in the decade ahead - a platform to try out the new approaches and new technologies that will help humans move deeper into the Solar System.