The Falcon Heavy briefly roared to life for the first time at NASA's Kennedy Space Center. All three boosters -- 27 engines in all -- were tested.
The thunderous booms could be heard at the press site three miles away, as huge white clouds of engine exhaust billowed into a clear blue sky.
Everything appeared normal: The 230-foot (70-meter) rocket stood tall and brilliantly white after the test on the historic pad once used by NASA's Apollo moon rockets and space shuttles.
The press site was busier than usual, as TV crews and other journalists gathered at midday for the test. There was no guarantee of a test firing Wednesday. SpaceX had fueled the rocket before, but then stood down for undisclosed reasons.
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Today's firing appeared to last for about 10 seconds. The Heavy -- a triple-size version of SpaceX's frequent flier, the Falcon 9 -- is tailor-made for spacecraft headed to the moon or Mars, as well as extra-big satellites bound for low- Earth orbit.
The Falcon 9 is routinely used to hoist satellites as well as space station cargo, and perhaps by the end of year, could be hauling crews for NASA, too.
NASA's Saturn V moon rocket, used during the late 1960s and early 1970s, still is the all-time champ when it comes to size and power. "I love that rocket so much," Musk said in a tweet last month.