Six volunteers will embark on an unprecedented simulation intended to mimic the timescale of a Mars mission.
An international team of volunteers is beginning a simulation of a manned mission to Mars.
Although the mission can replicate some aspects of a real journey, the so-called "scare factor" cannot be simulated.
The crew, controversially, contains no females.
Six men from Europe, Russia and China were Thursday locked away from the outside world for the next one-and-a-half years, in an unprecedented simulation of a manned mission to Mars.
One Chinese man, one Frenchman, one Italian and three Russians will spend the next 520 days in a 550-cubic-meter (19,400-cubic-foot) mock spaceship at a Moscow research institute to test how they cope with 18 months of isolation.
Dressed in blue overalls, the six gave the thumbs-up sign and grinned before the camera flashes as loved ones gave them an emotional send-off, some jokingly wishing them happy New Year already for 2011.
"See you in 520 days!" shouted Russian participant Sukhrob Kamolov, just before a scientist sealed shut the heavy iron door of the facility at around 1000 GMT.
Like in a proper Mars mission, the crew will have to live on food rations akin to those used by real astronauts and their only outside communication will be by email, with a delay of up to 40 minutes.
The hatch will only re-open when the experiment ends or if one of the all-male team pulls out -- in which case he will be deemed dead and his 'body' pushed out to space.
Newly-wed mission captain Alexei Sitev must now endure a long separation from his wife, just weeks after the two married.
"I am already missing him. I'm crying right now," added Irene Urbina, sister of Italian-Colombian volunteer Diego Urbina, who said he was motivated by his passion for space.
Controversially, no women have been selected for the experiment, called Mars 500.
Long days in the module in the Russian Institute for Biomedical Problems (IBMP) will be divided into eight hours each of sleep, work and leisure.
With books, language-study guides and 3-D videos games on board, Urbina said: "I don't think we'll get bored." Also in ebullient mood, Frenchman Romain Charles said he has brought a guitar "to annoy" crewmates.
Three of the team will briefly quit the mothership for a special module meant to imitate a Mars landing craft, while two will take mock spacewalks in a sand-filled bunker, donning 3-D specs to help induce the surface feel of the Red Planet.
Wang Yue, 27, a candidate astronaut of China's space program, told reporters before entering the capsule: "It is just a simulation. It is not a matter of life and death."
The idea is to exactly mimic the timescale of a Mars mission -- 250 days for the trip to Mars, 30 days on the surface and 240 days for the return journey, totalling 520 days.
"You cannot simulate everything. That is obvious," said Christer Fuglesang, head of science at the directorate for human spaceflight for the European Space Agency, a co-organizer of the project with the IBMP. "The scare factor cannot be simulated... that they might not come back."
The crew also conspicuously lacks women, meaning possible sexual-tension that could arise from a mixed-gender crew will not be examined.
Yury Karash, a Russian space policy expert, said the choice of an all-male crew would allow the team to focus on their duties and avoid unwitting competing for the attentions of female crew member.
"It is better for the crew to be same-sex," he said on Russian television. "No one has abolished the basic instinct yet."
Unlike a real spaceflight, mission participants will not be subjected to debilitation effects of weightlessness and ionizing radiation.
A real flight to Mars will not come before 20 to 25 years, ESA head Martin Zell estimated, but added such a mission was "absolutely realistic."
"The question is when and who?" Zell said.