An Orion mission to Mars was seriously considered. Due to the obvious problems which launching such a mission from the ground, it was decided that an upgraded Saturn V booster would be used to lift it into low earth orbit, but this constrained the diameter of the ship to around 10 meters. Additonal thrust at lift off would have been provided by 4 strap-on boosters, each one with its own F1 engine.Two launches would be needed to assemble the ship. The travel time to Mars would only have been around 125 days, much quicker than with rockets such as Nerva which would have taken approximately 2 years. During the unpowered 'cruise' portion of the flight, the whole vehicle would have been spun 'end over end' to provide the crew with artificial gravity.A crew of 6 or 8 would have made the trip, and the ship would have carried a 'Mars Excursion Vehicle' derived from lifting body research to carry the expedition to the surface and back.