SpaceX doesn't land its rockets back on ??????? ????? ??????Earth just because it looks cool.

Their real motive is simple: Cost.

Traditionally, rocket companies only use their rockets once, effectively wasting hardware that cost millions of dollars to build after just one use. These spent rockets are destined to either become space debris or fall back through Earth's atmosphere and burn up, leaving the charred leftovers to plummet into the ocean.

But SpaceX isn't into that model.

The Elon Musk-founded company landed its first Falcon 9 booster back on Earth in 2015, after years of development. In March 2017, SpaceX successfully relaunched a used rocket into space and then landed the expensive equipment back on Earth.

Today, SpaceX regularly brings its rockets safely back to Earth, landing on either the ground or in the ocean, on its drone ships. The company has now successfully performed more than 20 rocket landings, including landing two Falcon Heavy boosters back on land during the rocket's maiden flight in February 2018.

Reusable rocketry is a foundational reason why SpaceX has become one of the world's top rocket companies, just a decade and a half after Musk opened up shop in California with a half-dozen engineers. Reusing rockets lowers the cost of production, and accordingly, reduces launch costs.

As a private company, SpaceX isn't legally required to release its financial reports, like Apple or Facebook, and they're generally tight-lipped about their financial operations. That said, the company has released some vague information about its financials.

When speaking at a space conference about a refurbished SpaceX rocket, SpaceX President and COO Gwynne Shotwell said that "it was substantially less than half" the cost of building a new rocket booster.

The company advertises (to potential customers) that it costs $62 million to launch a Falcon 9 rocket into space. Analysts have mused that using refurbished rockets could lower this launch price by some $20 million -- or more.

Increasingly competitive pricing -- along with a reliable Falcon 9 rocket -- have made SpaceX an attractive rocket vendor to the likes of NASA, private companies, and other nations. These customers hire SpaceX to launch satellites and spacecraft -- some that cost hundreds of millions of dollars -- into space.

But SpaceX believes its greater ambitions -- to visit and set up shop in far-off parts of space like the moon and Mars -- also requires reusability.

"The only way we’re going to be exploring the solar system and being able to return — going to other planets and being able to return — is if these systems are reusable," Shotwell said.

"Otherwise they’re one-way trips."

Aside from the horror of being stranded on Mars, it would also likely be prohibitively expensive to manufacture a new rocket, with new engines, each time either SpaceX or another company wants to travel into a deeper part of space.

These unsustainable rocket costs contributed to why NASA stopped sending astronauts to the moon in 1972, three years after Neil Armstrong first set foot on the chalky, lunar surface. In 1969, NASA spent over half a billion dollars on four launches of the Saturn V rocket (not including many other missions costs), which today is the equivalent of more than $3.7 billion.

As of April 2018, SpaceX is only reusing the first stage of its Falcon 9 rocket. This bottom portion of the rocket contains nine custom-built engines.

Next, SpaceX hopes to reuse the very top of the rocket, called the fairing, which costs some $6 million to build. The company plans to catch the parachuting fairings in a large net attached to a ship.

According to Musk, SpaceX is also considering using a "giant party balloon" to bring another sizeable portion of the Falcon 9 rocket, called the second stage, safely down to Earth. If you can ignore the silly "party balloon" reference, this might be a realistic goal. Using a balloon to float the rocket down could mean that the rocket stage wouldn't need to save fuel required for a powered landing.

SpaceX has certainly had a lot of success sending satellites and goods into Earth's orbit, but it's unknown when the spaceflight company will actually send missions to the moon and beyond.

But for those that choose to journey to those desolate, freezing, inhospitable worlds, there may be comfort in knowing there's a way back home.

"If you go to Mars and don’t like it, it would be great if you can come back," said Shotwell.