You can simulate it, sure, but the most valuable lessons are learned during actual attempts. When things go poorly, those lessons are also the most expensive. The fact is, most missions to Mars don't make it, though NASA has a better track record than most. The agency has executed seven successful touchdowns on the red planet. On Monday, November 26th, it will attempt its eighth, when it endeavors to land the $830-million InSight spacecraft on Elysium Planitia, a vast plain just north of the Martian equator.