It has a jet engine's roar but not the accompanying whine-just an ear-shattering thunder. And the airplane is far too small, like a Volkswagen with a semi's air horn. It blasts down the runway, climbs steeply, and then hurtles away from the crowd lining the fences at Las Cruces Airport in New Mexico, dwindling rapidly into a clear October sky. The roar fades, disappears. The plane, dubbed the EZ-Rocket, sails through a turn, wings back toward the spectators. Rick Searfoss, the Air Force-trained test pilot and former space-shuttle commander at the controls, glides in silence until he relights one of the two isopropyl-alcohol-powered rocket engines. He banks left, blasting through a high S-curve at 160 mph to come back around parallel to the runway, and swings the rocket's faint blue exhaust toward the cheering crowd. These people have come to the first annual commercial- spaceship expo, the 2005 X Prize Cup, to see the next generation of rocket vehicles, and they aren't disappointed. But no one's having as much fun as Searfoss. "Let me just tell you, it's a kick in the pants," he exults after landing.