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Tuesday's success "taught me, like, crazy things can come true," Musk told ABC's David Kerley. "I didn't really think this would work."
Before launch, the billionaire said he would "consider it a win" if the rocket just made it off the pad. Now zooming through space at 11 km per second, the Falcon Heavy exceeded expectations. If all goes as planned, the Falcon Heavy and its unusual cargo will remain in orbit for up to a billion years, according to Musk.
"You can tell it's real because it looks so fake," Musk said of the images being beamed back.
The Falcon Heavy has three first-stage boosters, 27 engines in all. Stretching 40 feet at the base and standing 230 feet tall, the Heavy is a triple dose of the Falcon 9, the company's frequent flyer with just a single booster. At liftoff, the Heavy packs about 5 million pounds of thrust.
Two of the boosters returned to Earth, executing near-simultaneous, side-by-side touchdowns at Cape Canaveral. The third booster missed its landing barge and crashed into the ocean at 300 mph, spraying the barge with shrapnel, the company said.
Along with several other famous former astronauts, Buzz Aldrin, one of the first men to walk the moon, was watching as the Falcon Heavy took off from what he called "my favorite launchpad."
Even President Trump took to twitter to congratulate Musk's feat:
Congratulations @ElonMusk and @SpaceX on the successful #FalconHeavy launch. This achievement, along with @NASA’s commercial and international partners, continues to show American ingenuity at its best! pic.twitter.com/eZfLSpyJPK— Donald J. Trump (@realDonaldTrump) February 7, 2018
ABC News' Gina Sunseri and Julia Jacobo contributed to this report.