He aims to walk on Mars. First, though, Lindbergh High School senior Ryan Shelhorse will take on the U.S. Air Force Academy: jet planes and lots of physics. Then, NASA: space travel and — he strongly believes — walking on the Red Planet. “I really think it will happen in my lifetime; it’s just a feeling I have,” said Shelhorse, who is set to graduate Saturday with a 3.5 grade-point average.