Yesterday, SpaceX demonstrated an important capability of its Falcon 9 rocket fleet: the vehicles are capable of launching to space multiple times. From Cape Canaveral, Florida, the company relaunched a used Falcon 9 rocket that had already launched to the space station in April of last year. That same vehicle landed on one of SpaceX’s autonomous drone ships after launch and then went through months of refurbishment and testing to get ready for spaceflight again. And not only did it launch successfully a second time, but it landed on the drone ship again, too.

“This represents the culmination of 15 years of work at SpaceX to refly a rocket booster.”

The mission is an important proof-of-concept for SpaceX, which is trying to demonstrate that it can reliably reuse its orbital rockets again and again. “This represents the culmination of 15 years of work at SpaceX to refly a rocket booster,” CEO Elon Musk said at a press conference following the mission.

The entire endeavor to refly rockets is meant to be a cost-saving tactic. The most expensive part of the mission, according to Musk, is the Falcon 9 first stage — the 14-story core of the rocket that SpaceX tries to land after each launch. This stage, which contains the main engine and most of the fuel needed for launch, represents up to 70 percent of the cost of the mission. Musk notes that propellant for the rocket is only about 0.3 percent of the cost. That means saving these vehicles and flying them again could lead to a cost decrease by a factor of 100, Musk says.

In order for SpaceX to maximize the economic benefit of its reusable rockets, it’s going to have launch these used vehicles as frequently as possible. And it’s not as if the Falcon 9 rockets are ready to fly again as soon as they land. It took about four months to get this particular rocket ready for its second flight. Musk is challenging SpaceX to trim down that turnaround time, though. Eventually, he wants the inspection and refurbishment process to take just 24 hours to complete.

But SpaceX may have a lot of practice with refurbishing rockets, since the company is aiming to fly up to six preflown Falcon 9s this year. And it looks like we’ll see some used boosters on some significant upcoming flights; for instance, Musk notes that parts of the company’s future Falcon Heavy rocket will be used. The Falcon Heavy, which is supposed to make its flight debut this summer, is essentially comprised of three Falcon 9 cores strapped together. And Musk says that two of those three cores will have already flown to space and back.