Taking aim at a distant asteroid, SpaceX fired a small NASA probe into space early Wednesday, setting up a head-on 15,000 mph impact next September to test the feasibility of nudging a threatening body off course long before it could crash into Earth. The $330 million Double Asteroid Redirection Test, or DART, the first test flight in a NASA planetary defense initiative, "will be historic," said Tom Statler, mission program scientist at NASA Headquarters. "For the first time, humanity will change the motion of a natural celestial body in space." Perched atop a SpaceX Falcon 9 rocket, the DART mission...