On February 6, SpaceX made history with the largely successful first launch of its Falcon Heavy rocket—and National Geographic was there, right alongside SpaceX CEO Elon Musk.

In preparation for the second season of MARS, which is returning to Nat Geo this fall, a camera crew followed Musk and his team on the day of the launch, capturing their reactions as the rocket rumbled to life.

“Holy flying f--k, that thing took off,” Musk exclaimed. Moments later, he and SpaceX staffers ran out the door of the launch control center and turned their gazes upward. “Look at that! That's unreal!” Musk cried out.

As National Geographic reported from Cape Canaveral on Tuesday, the Falcon Heavy launch is a milestone for private companies' journey into space. At peak performance, the massive rocket can lift 141,000 pounds—equal to the weight of two adult sperm whales—into low-Earth orbit. Only NASA's Saturn V rocket, which carried astronauts to the moon, has lifted more that high.

But as Musk emphasized before and after the launch, success was hardly a given.

SpaceX announced its intention to build the Falcon Heavy in 2011, crafting it as a vehicle essentially made out of three combined Falcon 9s, the company's currently most-used rocket. At the time, Musk thought that the Falcon Heavy would launch in 2013, but the project promptly entered years of development hell. To make the Falcon Heavy work, SpaceX had to redesign the center booster completely, rework the control systems, and upgrade the fins that the reusable first stages use to steer so they can land back on Earth.

“We tried to cancel the Falcon Heavy program three times at SpaceX, because it [was] way harder than we thought," said Musk in a press briefing after the launch.

Now that the Falcon Heavy has flown, more work remains to refine the rocket and develop its successor, the so-called BFR booster and spaceship that he hopes will one day be bound for Mars. But above all, Musk's takeaway from the test flight was that he and his roughly 7,000 employees had pulled off something extraordinary.