Recently, a top Russian space agency official stated Russia and the United States should cooperate on a manned mission to Mars. NASA Administrator Charles Bolden agreed. Both men argued the scope and technological challenges of such an effort-- that is to say, the cost-- of going to Mars is beyond the reach of any one nation.
Among the challenges to be addressed are the development of a propulsion system that would allow missions to Mars to be flown as quickly as possible, as well as finding a way to protect crews against cancer-causing cosmic radiation.
The effort needn't be limited to two nations, either. An international coalition of several nations, Bolden said, is the way to go. Nothing formal is underway at the moment, but informal discussions seem to be bubbling around the world.