The crew of a mock trip to Mars ventured out after 257 days in a locked steel capsule to trudge into a sand-covered room and plant flags on a planet.
Three Russians, a Frenchman, an Italian-Colombian and a Chinese crew member entered a network of modules at a Moscow research centre last June to imitate the 520-day flight and see how they handle the constricted, isolating conditions of space travel - minus the weightlessness.
Several donned 30kg spacesuits to perform the mock landing in an adjacent capsule. They planted the flags of Russia, China and the European Space Agency, took "samples" from the ground and conducted mock scientific experiments.
"All systems have been working normally. The crew are feeling fine," said Vitaly Davydov, deputy head of the Russian space agency.
Psychologists said long confinement would put the team members under stress as they grow increasingly tired of each other's company. Psychological conditions can even be more challenging on a mock mission than a real flight because the crew will not experience any of the euphoria or dangers of actual space travel.
Mr Davydov described the experiment as an important part of preparation for flight to Mars and predicted that the real mission could take place in about 20 years, but only with international co-operation.
Martin Zell, a European Space Agency official overseeing the experiment, called the mission a "really strong asset for future undertakings of mankind in space, for its ambition to fly finally to the Red Planet".
The site for the experiment is in western Moscow and includes living compartments the size of a bus connected to several other modules for experiments and exercise. The mission director has said the experiment could be disrupted for medical or technical reasons, or if some of the participants demand it be stopped.
A real mission to Mars is decades away because of huge costs and massive technological challenges, particularly the task of creating a compact shield that will protect the crew from deadly space radiation. US President Barack Obama said last month that he foresaw sending astronauts to orbit Mars by the mid-2030s.
The experiment is being conducted by the Moscow-based Institute for Medical and Biological Problems in co-operation with the European Space Agency and China's space training centre.