landed the majority of the rocket on a floating drone ship at sea. It’s the second time

SpaceX has landed its rocket post-launch, and the first time the company has pulled

off an ocean landing.

This is another big milestone for SpaceX. In December, the company made history when

it successfully landed its Falcon 9 for the first time at a ground-based landing site

at Cape Canaveral, Florida. Sure Blue Origin has also launched and landed its own rocket,

but that vehicle can’t really be compared to the Falcon 9. And now SpaceX has shown

it is capable of landing its rockets both on solid ground and at sea.

But why land on a floating drone ship when you can land on land? It’s definitely easier

to touch down a rocket on a large, expanse of ground, rather than a ship floating on

moving water. Plus, all the previous times SpaceX has tried to land the Falcon 9 at sea,

the results have been… explosions.

The reason has to do with fuel. When the Falcon 9 reaches a certain altitude in space and

separates from the top of the vehicle, it uses leftover fuel to reignite its engines

and come back to Earth. The engines are lit in a series of burns that get the vehicle

in the right position for entering Earth’s atmosphere and landing.

Different landings require different amounts of fuel to pull off. It’s because the Falcon

9 doesn’t launch straight upward, but follows a curved path up and away from the launch

pad. For a ground landing, the rocket needs extra fuel to slow down on that arc, completely

flip around, and then retread all the horizontal and vertical distance it has covered to make

it back to solid ground.

But for ocean landings, the drone ship can position itself down range of the rocket,

or in the ideal place to "catch" the vehicle on a more natural path back to Earth. That

decreases the distance the rocket needs to travel and the amount of fuel needed to maneuver

the Falcon 9 for landing.

Not all of SpaceX’s missions are even capable of performing ground landings, since some

use up way more fuel than others. Rockets that launch heavy payloads or go to a high

orbit need extra speed for the initial launch. And extra speed requires extra fuel. So for

Falcon 9 vehicles that accelerate much more rapidly during ascent, there’s not as much

fuel leftover for the landing. That’s when the drone ship is the best — if not only

— option for recovery.

SpaceX expects to land about one-third of its rockets on land, and the rest in the ocean.

So it’s definitely going to need to perfect those sea landings in order to recover and

reuse more rockets in the future. The company’s president Gwynne Shotwell, expects reusing

the Falcon 9 will lead to a 30 percent reduction in launch costs. Those savings will only start

to benefit SpaceX with the more rockets they land, and the faster they land them.