SpaceX has resumed station deliveries for NASA. And this time, it has successfully landed its booster rocket on an ocean platform for the first time, after four previous failed attempts.

The reusable booster rocket landed after propelling the unmanned Dragon cargo spacecraft to orbit, carrying supplies for astronauts at the International Space Station, or ISS. The rocket also sent an inflatable room to space, which will attach to the ISS for a two year test. If successful, the room will become the first such habitat to hold humans in orbit. 

Last December, SpaceX successfully landed a Falcon 9 on ground for the first time. These landing attempts are part of the firm's effort to return costly rocket parts for repeated use and provide affordable private space travel. In a press conference following the launch, SpaceX CEO Elon Musk called the landing a "milestone".

"I think this is a really good milestone for the future of spaceflight.. I think it's another step towards the stars. In order for us to really open up access to space, we're got to achieve full and rapid re-usability and being able to do that for the primary rocket booster is going to be a huge impact on cost. Now, it'll still take us a few years to make that smooth and make it efficient, but I think it's proven that it can work," Musk said.