Irwin Stewart is one of the guides profiled in “Meet the Texperts! The State’s Best Tour Guides Want to Show You Around.” If you’ve been among the million-plus annual visitors to Space Center Houston, the museum at NASA’s Johnson Space Center, you’ve probably seen the Apollo 17 command module, walked through the replica of the space shuttle Independence, and touched a moon rock. You may have even taken a tram to the 1,600-acre working campus behind the museum and walked up to the Saturn V rocket—more than thirty stories tall—lying on its side like a giant in repose. But have you met Irwin Stewart?You don’t have to be a celebrity preparing for a movie about space to get a VIP tour from Stewart, though he has…