Humbled by Mars, NASA is about to send another spacecraft to study it. The launch of the 2001 Mars Odyssey orbiter, set for Saturday, is the first since the agency was staggered by 1999’s back-to-back failures of missions to the planet. And it is the first Mars craft to be dispatched since the National Aeronautics and Space Administration drastically revamped the program based on multiple investigations of what went wrong.