Launching anything into space is a very expensive business. SpaceX is reducing that cost by figuring out how to reuse parts of its Falcon 9 rocket. We've already seen the first-stage return to Earth and land, but now Elon Musk wants to get the second stage back, too.
The first stage of the Falcon 9 rocket consists of nine sea level adapted Merlin engines, where as the second stage only uses one vacuum adapted Merlin engine for delivery of the payload to a desired orbit. It's much more difficult to recover the second stage due to the heat shield, landing engines and other equipment required to achieve it. The additional mass was just too great to even consider trying it. However, there's now a new idea on the table, which Elon Musk shared with the world via Twitter.
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon— Elon Musk (@elonmusk) April 15, 2018
That's right. Forget the extra mass for a heat shield and engines, just use a giant balloon to slowly drop the second stage back down to Earth!
Controlling where the rocket would drop in the ocean would be handled with retro burns and SpaceX would deploy a "catcher ship" to the location in order to retrieve the rocket quickly.
Musk admits it sounds a bit crazy, but so did landing a rocket, let alone two in perfect sync, and we now all expect that to happen with every SpaceX launch. So, you really can't bet against SpaceX focusing in on the problem and developing a balloon that will make second stage recovery possible.