SpaceX and Tesla CEO Elon Musk. Reuters/Stephen Lam Long before SpaceX and Tesla CEO Elon Musk gained a net worth of an estimated $11.9 billion, or before he became a millionaire at 28 after selling his first company, Zip2, he lived off just a dollar a day.

Forcing himself to live mainly off hot dogs and oranges wasn't the result of poverty or some charitable movement, but an experiment to see if he had what it takes to lead a life as an entrepreneur, he tells astrophysicist Neil deGrasse Tyson in the latest episode of Tyson's StarTalk Radio podcast.

As they discuss Musk's early years, Musk explains his fascination as a freshman and sophomore at Queen's University in Ontario with how he could help shape the future of humanity through the internet, energy efficiency, and space exploration.

Tyson jokes that most undergraduates are mostly focused on how they're going to get a job after graduation.

Musk says that concerned him, as well. His plan was always to go to the US — he transferred to UPenn as a junior — and so he imagined what it would be like as a 20-something in the US foregoing a job to start his own technology business.

"I mean, in America it's pretty easy to keep yourself alive," he tells Tyson. "So my threshold for existing was pretty low. I figured I could be in some cheap apartment with my computer and be okay, and not starve."

He decided to see if a $30 food budget could get him through a month. He bought mostly hot dogs and oranges in bulk, and would occasionally switch it up with some pasta and jarred tomato sauce. He pulled it off.

"So I was like, 'Oh, okay. If I can live for a dollar a day — at least from a food cost standpoint — it's pretty easy to earn $30 dollars in a month, so I'll probably be ok," Musk says.

It gave him the assurance that he didn't need a comfortable salary to survive, allowing him the freedom to pursue his loftier goals, he says.

"Not to put words in your mouth, but that's a starting point to launch anywhere you want to go," Tyson says.

"Yeah. Absolutely," Musk replies.

You can listen to the full StarTalk episode below: