There couldn't have been a more perfect launch than yesterday's. The sun was shining, a gentle breeze was blowing, and SpaceX's Falcon 9 rocket took off right on schedule. As we watched from a few miles away, the glare of the rocket's flames was searingly bright, hard to look at but impossible to look away from, like the sparklers kids play with on the Fourth of July. The sound, too, was like Independence Day, the boom and shake of a thousand fireworks going off, crashing through the sound barrier.

The cargo made it safely into orbit, where it's on its way to the International Space Station. But the real magic was in what happened after the launch. For the first time ever, the Falcon 9 came down for a gentle (non-explosive) landing on a drone ship. The achievement is critical in developing reusable, relatively low-cost spaceflight.

"It's another step toward the stars," said Musk during a press conference.

Traditionally, rocket boosters fall into the ocean after launch, never to be used again. But Musk often compares that to throwing away an airplane after every flight. Reusing the booster could shave millions of dollars off of launch costs, and the first step to that is getting the boosters back to Earth safely.

"It's another step toward the stars."

SpaceX landed its rocket on solid ground in December, but landing on the drone ship was key to SpaceX's reusability strategy.

That's because about half of all launches bring the rocket over the ocean. After that, the rocket doesn't have enough fuel to turn back around and head for land. The autonomous ship gives SpaceX a movable landing pad, but landing on it proved difficult. It's akin to a jet landing on an aircraft carrier—the target is small and moving—except that the rocket comes down at about 17,000 miles per hour.