Crewed Mars missions will require a new ascent vehicle

America has a once-in-a-generation opportunity to open the space frontier by initiating a sustained program of human exploration of Mars. Elon Musk’s SpaceX Starship launch system may soon be operational, offering payload delivery capability comparable to a Saturn V moon rocket at about 5% the cost. President Trump has announced that he plans on sending humans to Mars. But how can this be accomplished?