One year
NASA is getting interested in having astronauts spend a whole year in space! The idea is on its way!
It had been difficult for Romanenko to spend 326 days in space, a little less for Titov and Manarov to spend 1 year aboard Mir and still less for Krikalev to spend 10 months even though he hadn't prepared for it.
Polyakov was very well prepared for his 14 months!
One of the main reasons was that Mir kept growing with more and more room for the cosmonauts (for privacy, for instance).
But a spaceship for Mars wiil have far less room for the astronauts than the current stations.
Raoul