Elon Musk just tweeted the image below of the Falcon 9 rocket landing vertically in the ocean, right before it splashed down.

The rocket was launched on April 18 during a resupply mission to the International Space Station. It fulfilled its main mission of delivering cargo, but the launch was also a test of the rocket's reusability — it was the first time they flew the rocket with the "landing legs" attached, which play a crucial role in getting the rocket to land vertically. 

While they weren't successful in recovering the rocket stage because of rough ocean conditions, the data (and this image) show the rocket successfully navigated its way down through the atmosphere by reigniting its rockets, then was able to position itself vertically in a landing position. 

Successfully recovering the rocket will help to greatly reduce the cost of rocket launches — which deliver cargo to the International Space Station and satellites into orbit. In the future, SpaceX wants to help bring astronauts up to the ISS as well, replacing the need to rely on the Russian Soyuz rockets. 

In the image below you can see the rocket's "landing legs" deployed and the engines engaged, kicking up water. The camera seems to be positioned on the side of the rocket looking down into the ocean:
elon falcon 9 spashdown spacexSpaceX / Elon Musk Twitter

Here's the tweet, in which Musk teases that there's also a video: