With funding from NASA, the company is working to make rockets reusable. The logic is that you don't throw out a Boeing 747 after every flight, so why make one-time-use rockets? If the company can find a way to reuse rockets, it could significantly reduce the cost it takes to shuttle people and supplies into space. It's hard to repurpose a rocket after it's fallen into the salty Atlantic—which is why the company is working so hard to land the rocket softly and in the upright position.

Sunday will be SpaceX's third attempt to land the Falcon 9. On the first attempt, in January, SpaceX says the rocket ran out of the hydraulic fluid that steers the fins that help control the rocket's descent. As a result, the rocket came down too hard.

The second try in April came down slower, but still ended up toppling over.

In this case, a valve that controls the rocket's thrust grew sluggish near the end of the flight. “With the throttle essentially stuck on “high” and the engine firing longer than it was supposed to,” SpaceX explains, “the vehicle temporarily lost control and was unable to recover in time for landing, eventually tipping over.”

Hopefully the third time's a charm. The company says they've fixed the problems and made changes to be able to compensate for the sticky valve if it happens again.

The launch is scheduled for takeoff at 10:21am Eastern on Sunday (0020h Monday for us, ech), and the historic landing attempt shortly afterwards.