On Sun. Jan. 17, Elon Musk’s SpaceX launched its fourth rocket to land one safely at sea.

Initially, SpaceX revealed that the rocket suffered a hard landing. Later, the company explained that one of the legs failed to latch on the landing platform.

Musk said, “[The] root cause may have been ice buildup due to condensation from heavy fog at liftoff.”

The first mission of the rocket was successfully done in order to carry a satellite into low orbit. The secondary mission is to land the rocket upright on a platform  in the air called a drone ship. Musk was not able to complete the second mission.

Musk said, “Falcon lands on drone ship, but the lockout collet doesn’t latch on one [of] the four legs, causing it to tip over post-landing.”

In addition, Musk is planning to make these rockets reusable to save money, resources, and improve efficiency. Currently, SpaceX rockets cost about $60 million to $90 million, so the ability to reuse the rocket would reduce the cost of space travel exponentially.

In December 2015, SpaceX successfully landed one of its Falcon 9 rockets on land from Florida’s Cape Canaveral Air Force Station.

SpaceX launched Sunday’s rocket from the Vandenberg Air Force Base in California for NASA. The satellite (Jason-3) will determine the ocean levels on the Earth’s surface.

NASA said, “Jason-3 data will be used for monitoring global sea level rise, researching human impacts on oceans, aiding prediction of hurricane intensity, and operational marine navigation.”