SpaceX hit a huge milestone today. For more than a year, the private spaceflight company has been attempting to land its rocket boosters on a drone ship in the ocean, and today they finally did it.

Landing the rocket boosters is key to being able to reuse them, cutting millions of dollars off of launch costs in the process. The cost to construct the Falcon 9 is about $60 million, compared to just a few thousand dollars to refuel it. There would be some costs to inspect, repair, and clean the rocket to ensure it's safe to fly, but Musk thinks each booster could potentially be used 10 to 20, or in some cases up to 100 times.

And while SpaceX's first recovered rocket, which landed on solid ground, will likely be installed as a monument at the company's headquarters, Musk says they hope to fly this one again. It'll be the first time SpaceX has flown a used rocket.