Some college students play intramural softball or pledge frats. Tim Ellis and Jordan Noone joined the Rocket Propulsion Lab.

"We wanted to be the first student group in the world to launch a rocket into space," Ellis says of the friends' time at the University of Southern California. "Something entirely of our own design and our own creation."

Though their rockets didn't quite make it to suborbital space, the group did pull off dozens of successful launches. Now, a few years later, Ellis and Noone are co-founders of Relativity Space, a startup that's building rockets that are almost entirely 3-D printed

A space-faring rocket built by traditional manufacturing methods consists of about 100,000 parts. By printing large components that need far less assembling, the co-founders say they can get that number down to 1,000. That will drastically reduce the cost and time needed to build a rocket: While it normally takes about 12 to 18 months to construct one, Ellis says Relativity will be able to do so in just 60 days.

"Plus, it's very flexible," Ellis says. "You can iterate a new design on your software and deploy it super quickly."

The co-founders conceived of the idea while working in the space industry shortly after college--Ellis with Blue Origin, Noone with SpaceX. Within their respective teams, both were working on 3-D printing rocket components. Soon they started wondering: Why not print the whole thing? Separately, they pitched the idea of leaning more heavily on 3-D printing within their respective companies, with Ellis getting to present his directly to Jeff Bezos. But the proposals never fully caught on. "It would have been a hard left turn for them," Ellis says.

So they decided to branch off and try it themselves. One day in late 2015, they fired off a cold email to Mark Cuban with the subject line "Space Is Sexy: 3-D Print a Whole Rocket." Cuban wrote back within five minutes. Within a week, he'd agreed to invest $500,000 to fund their seed round; they soon earned an investment from startup accelerator Y Combinator as well. 

A little more than two years later, Ellis and Noone are the CEO and CTO, respectively, of the 17-employee Relativity Space. The company has already built an entirely 3-D printed rocket engine, which it's tested nearly 100 times. While a traditional engine is made up of about 2,700 parts, Relativity's consists of just three.

To do that, the team built what Ellis calls "the largest metal 3-D printer in the world"--about the size of a classroom. For smaller pieces, it uses off-the-shelf printers. The completed rocket will be smaller than those produced by Musk's and Bezos's companies--seven feet in diameter and 90 feet tall, perfect for the medium payloads the startup is pursuing. In all, the co-founders say they can build a rocket that's 95 percent 3-D printed, with the exceptions being things like seals and computer chips (though they say the business blueprint has them one day printing those as well).

In March, the company inked a contract with NASA to use the Stennis Space Center for rocket tests. And Ellis says Relativity has $1 billion in letter-of-intent launch contracts, largely with companies looking to send up midsize satellites about the size of a car. Because of the relative cheapness of its manufacturing methods, he says the company will be able to charge $10 million for a 1,250-kilogram payload--about one-third the price of what its competitors charge. 

"Looking forward 50 years," Ellis says, "I can't see a future where things that fly are not entirely 3-D printed."

That includes things that fly from other planets, which touches on one of Relativity's even more ambitious goals. While Musk wants to find a way to get humans to Mars, the co-founders want to help get them home--by 3-D printing rockets on other planets. And they hope those printers will be able to churn out more than just spacecraft.

"We see this reducing the amount of infrastructure you need to send from Earth to Mars to make a sustainable colony," Noone says. "In traditional manufacturing, you have a ton of factories full of machinery to make any sort of hardware, be it a car, a house, a propellant depot. We want to see a future where you just send a printer that can print from Mars's soil."

Ellis and Noone aren't the only ones excited about the startup's future prospects. In March, the company announced a $35 million Series B round led by VC firm Playground Global, which brings the company's total funding to $45 million. 

"The work that they've done designing and executing on their engine is really impressive," says Jory Bell, partner at Playground, which had former SpaceX employees study Relativity's architecture before deciding to invest in its Series A. "And every technical decision they've made is optimized not only to serve their initial market, but to scale up as well."

Of course, successfully testing an engine is one thing--building and launching an entire rocket is another. For now, the co-founders say they want to blast off sometime in 2020. 

"We see a lot of opportunity," Ellis says. "Three-dimensional printing is the future of building rockets and the future of space."

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