An explosion at a Mojave Desert airport during testing of a propellant system for a new space tourism vehicle left three workers dead, and has shaken a small community that prides itself as the hometown of the first private space launch. The blast Thursday at a remote test facility belonging to Scaled Composites LLC also critically injured three others. The accident occurred during a test of the flow of nitrous oxide through an injector in the course of testing components for a new rocket motor for the SpaceShipTwo. The chemical was at room temperature and under pressure, Rutan said. The company, headed by maverick aerospace designer Burt Rutan, made history in 2004 when its SpaceShipOne became the first private manned rocket to reach space. Since that milestone, Rutan has partnered with British billionaire Richard Branson to build a fleet of commercial vehicles dubbed SpaceShipTwo for Virgin Galactic.