At least one non-governmental group, calling itself the Mars Society, has been actively studying technologies appropriate to send a crew of from four to six astronauts to Mars for a roughly two-year stay.<ref name=marssoc>[http://www.marssociety.org/portal The Mars Society] global and USA portal. Accessed May 27, 2008.</ref> | At least one non-governmental group, calling itself the Mars Society, has been actively studying technologies appropriate to send a crew of from four to six astronauts to Mars for a roughly two-year stay.<ref name=marssoc>[http://www.marssociety.org/portal The Mars Society] global and USA portal. Accessed May 27, 2008.</ref> |