SpaceX has become adept in the past two years at bringing first-stage boosters home after they have completed their primary task of getting a payload out of the thicker lower-reaches of the atmosphere.
The segments autonomously guide themselves back to the floating platform or a coastal pad to make propulsive landings.
Thursday's mission was the first time one of these "flight proven" vehicles had been re-launched.
Other landed boosters will now be used on future missions. Another six this year, most likely.
It sounds like a minor thing, but this is big deal in making space flight affordable. A business built on throwing half your capital investment away after just one use is never going to work. SpaceX have now proven you can spread the cost of a booster over several flights. Yes, the Shuttle did it decades ago, but NASA abandoned that line of development almost as soon as they started it.