SpaceX just announced that its Falcon Heavy rocket has successfully completed testing on its three first stage cores, a huge development that is being hailed by company founder Elon Musk as a critical step for the company. SpaceX first announced the Falcon Heavy, which is much bigger than the Falcon 9 used to power SpaceX rockets today, back in 2011, but it had endured multiple delays.

In testing that took place at a company facility in Texas, and months after the first static test of the Falcon Heavy rocket, the rocket fired off one of its cores, and SpaceX posted the brief video online.

Falcon Heavy is so big, it’s basically like three Falcon 9 rockets strapped together. It would be the biggest rocket SpaceX has ever launched, capable of blasting 140,000 pounds into space, compared to just 50,000 pounds for the Falcon 9. And like the Falcon 9, Musk intends to make them recoverable after launch by landing them on the surface of the Earth. It could one day send man to Mars.

“When Falcon Heavy lifts off in 2017, it will be the most powerful operational rocket in the world by a factor of two,” reads a SpaceX statement. “With the ability to lift into orbit over 54 metric tons (119,000 lb)–a mass equivalent to a 737 jetliner loaded with passengers, crew, luggage and fuel–Falcon Heavy can lift more than twice the payload of the next closest operational vehicle, the Delta IV Heavy, at one-third the cost. Falcon Heavy draws upon the proven heritage and reliability of Falcon 9. Its first stage is composed of three Falcon 9 nine-engine cores whose 27 Merlin engines together generate more than 5 million pounds of thrust at liftoff, equal to approximately eighteen 747 aircraft. Only the Saturn V moon rocket, last flown in 1973, delivered more payload to orbit. Falcon Heavy was designed from the outset to carry humans into space and restores the possibility of flying missions with crew to the Moon or Mars.”