An explosion at an airport home to Scaled Composites -- the builder of the first private manned rocket to reach space -- killed two people and left four seriously hurt Thursday, a Kern County Fire Department official says.art.mojave.kcal.jpgA bird's eye view of the scene in Mojave, California, shows charred wreckage and large pieces of debris.Click to view previous image1 of 2Click to view next imageIt happened at the Mojave Air and Space Port during a test of a new rocket motor for SpaceShipTwo -- a spaceship being built for Virgin Galactic, Richard Branson's space tourism company, a source said. The motor uses nitrous oxide, the source said.A spokeswoman for the spaceport, about 80 miles north of Los Angeles, said the blast was on a remote pad.Aerial video of the blast aftermath showed a charred and twisted flatbed trailer attached to a truck cab with a large silver tank next to it. Large pieces of debris appeared to be strewn for hundreds of yards from the center. Video Watch the aftermath of the explosion »About 200 yards away was a bunker with a truck owned by Scaled Composites, the aerospace development company founded 25 years ago by Burt Rutan, the aerospace engineer who designed the first plane to fly nonstop around the world without refueling.advertisementAn employee answering the phone at Scaled Composites would not answer questions when CNN called about an hour after the explosion.Rutan told CNN he was not at the spaceport at the time of the explosion, which he said happened during a "cold fire test."