SpaceX has teased rocket aficionados with the prospect of a Falcon Heavy booster launch for the better part of this decade. First, it was going to fly in 2014, then 2015, and so on. Now SpaceX is targeting the second half of this year, and perhaps we finally have cause to believe the rocket company will deliver.

That's because SpaceX has started to reveal bits of real hardware. First, the company shared an image last December of the Falcon Heavy's interstage being prepped at the rocket factory in California. Now, SpaceX has taken a significant step forward by conducting the first static fire test of the rocket's critical center core. This test was completed at its development facility in McGregor, Texas last week. Spoiler alert—the test was successful.

First static fire test of a Falcon Heavy center core completed at our McGregor, TX rocket development facility last week. pic.twitter.com/tHUHc1QiKG — SpaceX (@SpaceX) May 9, 2017

So what has taken so long? Earlier this year during a news conference, SpaceX CEO Elon Musk explained the delays by saying that developing the Falcon Heavy had proven more difficult than anticipated. "At first it sounded easy, but actually, no, this is crazy hard," Musk said. The company has had to redesign the center core and additional hardware for the upcoming flight, which he deemed to be a fairly high-risk mission. To save funds, the company plans to use two "flight proven" Falcon 9 cores as the side boosters around the center core tested last week.

Flying the Falcon Heavy will be a significant engineering achievement because the rocket is so technically complex. The Falcon Heavy has a first stage composed of three Falcon 9 cores, which have a combined 5 million pounds of thrust at liftoff from 27 Merlin engines.

Some critics of the rocket have said they don't expect it to ever fly because of this complexity. They have suggested that any booster relying on 27 engines to work in concert will be too unwieldy to rely upon for consistent launches. (These fears are likely fueled by memories of the unsuccessful Soviet N1 booster, which used 30 engines in its first stage and suffered failures on all four of its launches between 1969 and 1972.)

However, SpaceX has big plans for the Falcon Heavy. The company has said it could send a pair of space tourists on a flight around the Moon as early as next year, and it has plans to begin sending uncrewed spacecraft to Mars by 2020. Both of these missions would require the Falcon Heavy to fly successfully soon. This now seems more likely than ever.