SpaceX has done its first test of the Raptor rocket engine that will take humans to Mars as early as 2024, Elon Musk said in a series of tweets. It was fired at the company's McGregor, Texas facility on a stand that can handle the extreme thrust. Pointing out the "mach diamonds" from the test (above), Musk said the "production Raptor goal is a specific impulse of 382 seconds and thrust of 3 MN [680,000 pounds]," more than three times that of the current Falcon 9.