I haven't seen the concepts for a Mars mission but I'd imagine they'd dock with another module for the long journey to Mars. The Orion capsule would in that case provide a means to get astronauts to orbit, for general living space on the way to and from Mars (as part of a larger structure as I said), and for Earth re-entry.They think people could go to Mars in that? But that thing looks pretty tiny for something that'd have to make such a long journey.