Dinges' subjects were six men -- three Russians, two European and one Chinese -- who spent 520 days sealed inside a spaceship-like, windowless chamber at the Russian Institute for Biomedical Problems in Moscow for a Mars mission simulation.
"We wanted to get some idea of what will happen when a motivated, high-performing crew is confined in a spacecraft-like environment for a full 17 months, simulating a mission to Mars and back," Dinges said.
So far, only four people -- all Russian -- have made spaceflights lasting more than a year. The single longest human spaceflight was a 437-day mission aboard the Russian Mir space by Valery Polyakov, a physician, in 1994 and 1995.
The 520-day ground simulation, which ended on Nov. 4, 2011, showed that four of the six crewmembers suffered from sleep disorders, including one subject who ended up on a 25-hour day and another who split his sleep into two cycles within a 24-hour period. Such disconnects could affect a crew's ability to work as a team, among other problems, researchers write in a study published last week in the Proceedings of the National Academy of Sciences.