The time for SpaceX to finally test its reusable rocket technology is quickly approaching.

In June, SpaceX CEO Elon Musk announced that we could see one of the retrieved Falcon 9 rockets be reused as early as September.

And now, after months of deliberation, the company has plucked one of its famed Falcon 9 rockets from the pack and is preparing it for a momentous second trip into space.

SpaceX landed its first rocket on land in December. In April, for the first time ever, SpaceX managed to land at sea. The company has only been getting better at sea landings, nailing one on May 6 and another on May 27. And on Monday, the company went back to the basics, striking the target with another landing back on Earth.

Landing the first stage of its rockets is the first step in SpaceX's journey toward dramatically reducing the cost of spaceflight. By reusing these first stages, SpaceX estimates it could cut costs by as much as 30%.

SpaceX would not be the first company to reuse its rockets — Jeff Bezos' private spaceflight company Blue Origin has already landed and relaunched the same New Shepard rocket a total of four times.

But SpaceX would be the first company to successfully relaunch a rocket landed at sea.

So which of these lucky rockets gets to make history and prove SpaceX's reusable technology?

Musk said he wants to preserve the very first Falcon 9 SpaceX landed as a monument. And the third rocket took too much damage during reentry to be relaunched, so that rocket will be used for ground tests. So, during a NASA presentation, SpaceX announced that it has chosen the second successfully-landed rocket (and the very first to complete a sea landing) as the one to send on a second trip into space.

SpaceX's goal is to make almost all of its Falcon 9 rockets reusable, which would cut the cost of spaceflight by millions of dollars. A Falcon 9 might fly as many as 100 times before retirement, Musk told Ars Technica in April.