The last man to walk on the moon says he can’t explain what it was like up there but that more and more people may learn soon enough — thanks to a trillion-dollar industry hidden in the lunar dust. Dr. Harrison “Jack” Schmitt, 90, an Apollo 17 astronaut who spent three days on the moon in 1972, told The Post this week that there is a superfuel locked within the lunar dust that could provide Earth with an abundance of clean and safe energy for generations. “I’ve been working on this for many