An orbital-class rocket was successfully reused for the first time.
The SpaceX Falcon 9 was used to carry a satellite into near-Earth orbit. What was particularly astounding about this otherwise routine flight was that it re-used the first-stage booster from a previous Falcon 9 flight. The booster is the most expensive part of a Falcon 9, so being able to reuse this was a huge milestone in the history of spaceflight.