Three people were killed and three injured during a test of a propulsion system for Scaled Composites, the makers of SpaceShipOne and the work-in-progress, SpaceShipTwo.

According to this Yahoo article, "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."

The blast occured Thursday evening. As of Friday morning, two people were in critical condition, and one in serious condition.

Testing and development of SpaceShipTwo will continue.