Fireball during testing delays ULA's Vulcan rocket launch debut.

United Launch Alliance's plans for the first launch of its new Vulcan rocket have been delayed after a Centaur upper stage suffered an explosion during testing at NASA's Marshall Space Flight Center in Alabama. The incident was caused by a hydrogen leak that ignited. The upper stage that exploded was not part of the hardware for the first launch, but the investigation needs to be completed before Vulcan is clear to fly. The first Vulcan flight is likely going to be delayed into June or July.