Propane burners "loosely modeled on the thrusters from the space shuttle" heat the air that lifts today's hot-air balloons, notes Andy Richardson, owner of balloon manufacturer National Ballooning in Albuquerque, N.M. This is a far cry from the silk and paper balloons centuries ago that depended on ground-based fires for their short flights. Quite a bit of engineering goes into the balloon as well, Richardson says, with "a load building structure and the webbing works almost like an exoskeleton. When you’re designing balloons you take into account stressing of the fabric, the cables the balloon runs to, and the basket."
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