SpaceX launched its Falcon 9 to the International Space Station and has already landed the rocket on a drone ship, marking the first time the company not only sent cargo to the station following a failed resupply mission but also the first time it's successfully completed an ocean landing.
The rocket carried a Dragon cargo spacecraft stuffed with nearly 7,000 pounds of supplies for the station as well as an expandable habitat that will allow for astronauts to move around. It's also carrying up a several science experiments, including one experiment that will help investigators study muscle atrophy and bone loss in space. There's even cabbage that will be grown and consumed by ISS crew members.
The Dragon is expected to dock on Sunday but will return to Earth on 11 May with important samples, such as body samples taken by astronaut Scott Kelly during his extended stay in space. This launch is one of many SpaceX (which has contracts with NASA) ISS resupply missions over the next 8 years. It's sent cargo to the station six times. One attempt failed in June, however, due to a faulty strut in a fuel tank.
After the rocket launched today, SpaceX landed a part of the vehicle on a floating drone ship at sea. SpaceX has only successfully landed a rocket post-launch just once - and that was in December at a ground-based landing site in Florida. The ocean landing today is the second time SpaceX has successfully landed its rocket, and it's doubly significant because it shows SpaceX can handle two different types of landings.
It's also significant because it shows SpaceX can recover and reuse rockets, thus reducing the cost of resupply missions in space.