An explosion rocked a SpaceX launch site Thursday at Cape Canaveral in Florida, during a routine Falcon 9 rocket test. According to NASA, SpaceX was conducting a test firing of its unmanned rocket when the blast occurred. The test was in advance of a planned Saturday launch from Cape Canaveral Air Force Station, which is next to NASA’s Kennedy Space Center. Buildings several miles away shook and multiple explosions continued for several minutes. Dark smoke plumes filled the sky. A half-hour later, a black cloud hung low across the eastern horizon.