If you’re wondering why you’re spending another Labor Day holiday roasting weenies in the backyard instead of enjoying the scenery on a jaunt to the Red Planet, join the club. Robert Zubrin can’t understand it either. And he’s president of the club. Zubrin, a former Lockheed Martin engineer and founder of Pioneer Astronautics in Lakewood, is president of the Mars Society, which was founded in 1998 to encourage exploration of the planet. The society began with 600 international members. In five years, it has expanded to 6,000.