Relativity Space is a 3D-rocket-printing startup founded by engineers named Tim Ellis and Jordan Noone.

The two didn't have many connections in the investing world, so when they built their company, they decided to send Mark Cuban a cold email.

Ellis said Cuban agreed over email to fund their entire $500,000 seed round.

Tim Ellis has an audacious vision for the future of his company, Relativity Space: He's making a 3D printer that he hopes will someday be used to manufacture rockets on Mars.

While Ellis' vision might seem like the stuff of science fiction, he says that he's never once doubted his plan for his company and that this confidence has led to several successful funding rounds.

Since founding Relativity Space in 2013, Ellis and his cofounder, Jordan Noone, have received a total of $45.1 million from investors including Social Capital, Y Combinator, and the legendary "Shark Tank" investor Mark Cuban.

Cuban has a long history with Relativity Space. Ellis says Cuban first agreed over an email exchange to invest in the ambitious 3D-printing company.

"The week when we decided to start building our own company, we realized that we didn't have any connections in the investing world," Ellis told Business Insider.

Ellis and Noone, who have worked as engineers at Blue Origins and SpaceX, respectively, took an unorthodox approach to securing funding. After they heard that Cuban responded to cold emails, they decided to pitch their idea for Relativity Space to his inbox.

"We didn't have his email address, so we guessed a bunch of different combinations and tried them out," Ellis said. "It turns out that his email address is pretty easy to guess."

Once the two landed their pitch in the appropriate inbox, it took a few short moments for Cuban to respond. He was in.

Though Ellis and Noone originally asked for $100,000, Cuban volunteered to fund their entire seed round at five times the amount, Ellis said, adding that the entire exchange took about five minutes.

"I was impressed at his email game to get back to us that fast," Ellis said.

When asked what it was about his pitch that made it so compelling, Ellis said he believes the concept for Relativity Space is innately attractive.

"Space is sexy," Ellis said. "I think the idea of 3D printing an entire rocket really appeals to people."

Ellis said that reaching out to Cuban taught him an important lesson about asking for help in building his company.

"If you have a vision that people want to see happen, and you explain it clearly, people are usually very receptive to helping or putting you in touch with someone who can help," Ellis said. "There's a lot of people who want to back great ideas and great companies."

Asking for help has landed Ellis other beneficial connections for his company as well, among them a seat on the National Space Council's Users Advisory Group, which advises on government decisions about outer space. Ellis said he was the board's youngest member and the only one coming from a venture-backed startup.

While many startups won't speak with the government early on, Ellis said, he testified before senators to give perspective on what it's like to come from a venture-backed company. The move paid off in big ways — Ellis said his government connections landed him a 20-year agreement to use one of NASA's facilities at cost, saving him what he estimates to be hundreds of millions of dollars in overhead.

Ellis rarely hesitates to reach out when it comes to furthering the interests of his company, he said.

"You might as well reach out," he said. "Basically the moment you decide not to try, you're already sealing your fate."