Some things, like gum and diapers, are designed to only be used once. According to SpaceX though, their Falcon 9 rocket is not one of those things. For the first time ever, SpaceX has launched and landed a rocket that had flown to space before. This historic milestone was described as a "huge revolution in spaceflight" by SpaceX CEO Elon Musk following the mission. The rocket carried a communications satellite to orbit that will provide service to Latin America. This rocket was previously flown in April of last year.
SpaceX started working 6 years ago to try to make their rockets reusable, something Musk has envisioned for a decade and a half. Before this point however, SpaceX had to build and test an entirely new rocket for every launch. This ended up costing tens of millions of dollars to do. The actual part that is reused is the core which houses the main engines and most of the rocket fuel.
In addition to this, SpaceX recovered the Falcon 9's $6 million nose cone for the first time as well.
Following a launch, the rocket core is rigorously inspected and tested to ensure there is no damage. This process currently takes up to four months, but getting this time down is beneficial for both SpaceX and its customers. Musk's next goal is to be able to relaunch a rocket within 24 hours of its previous flight.
Evidently, one of the primary benefits to reusing rockets is the cost savings. SpaceX is estimating about a 30% reduction compared to a new rocket. This means launches could start around $40 million, an unthinkably low cost in the not to distant past. Although they don't fly anymore, NASA's Space Shuttle and its boosters were also reusable. SpaceX has plans to launch up to 6 additional second-hand rockets later this year.