Another one of SpaceX’s Falcon 9 rockets successfully landed on a floating drone ship this evening, after the vehicle launched a Japanese communications satellite into orbit. The feat marks the fourth time SpaceX has landed one of its vehicles at sea and the company’s fifth rocket recovery overall this year.

NOW SPACEX HAS A TOTAL OF SIX RECOVERED FALCON 9 ROCKETS

Tonight’s landing was particularly challenging for SpaceX, too. The Falcon 9 had to carry its onboard satellite — called JCSAT-16 — into geostationary transfer orbit (GTO). It’s a highly elliptical orbit that takes the satellite 20,000 miles out beyond Earth’s surface. Getting to GTO requires a lot of speed and uses up a lot of fuel during take off, more so than getting to lower Earth orbit. That makes things difficult for the rocket landing afterward. Not only is the rocket subjected to “extreme velocities and re-entry heating” during its fall back to Earth, according to SpaceX, but there’s less fuel leftover for the vehicle to reignite its engines and perform the necessary landing maneuvers.

Despite these challenges, SpaceX has managed to land three rockets bound for GTO — including tonight’s vehicle. In fact, the company now has experienced more success than failure with its rocket recoveries. Of SpaceX’s 11 rocket landing attempts over the past two years, six Falcon 9 vehicles have successfully made it back to Earth in tact.

SPACEX HAS YET TO ACTUALLY REUSE ANY OF ITS VEHICLES

But as the stockpile of recovered rockets continues to grow, SpaceX has yet to actually reuse any of its vehicles. CEO Elon Musk said the company is aiming to launch its first landed rocket sometime this fall, either in September or October. The plan is to re-launch the Falcon 9 that SpaceX landed in April, but the company has yet to say what the rocket will carry into space.

The hope is that by reusing these rockets, SpaceX will be able to reduce a big chunk of its manufacturing costs. Up until now, nearly all rockets have been expendable, meaning they are either destroyed or unrecovered after launch. Reusing an already launched vehicle saves SpaceX from having to build an entirely new rocket for each mission. SpaceX’s president, Gwynne Shotwell, estimates that reusing these landed Falcon 9 vehicles will lead to a 30 percent reduction in launch costs, according to Space News.