Nowadays, discussions about the future of space are more likely to reference private companies like SpaceX, Virgin Galactic and Blue Origin than NASA — the federal agency responsible for putting a man on the moon.

On Thursday, the Trump administration released a set of guidelines to reform and update U.S. policy toward private space endeavors. Tellingly, NASA's sole mention came at the end of the document announcing President Donald Trump's directive, where he called for the space agency to "return American astronauts to the moon, followed by human missions to Mars."

U.S. astronaut Peggy Whitson, who's been making the rounds in the media recently to promote "One Strange Rock" — a series about the complexity of human life on earth — told CNBC in an interview that another journey to the moon was advisable before aiming for Mars. There are lessons that need to be learned before undertaking a farther and riskier journey to the red planet, she said.

"Going to the moon first is smart, just like we're learning about how longer duration in space is smart," said Whitson, who spent so many days in orbit that one of her colleagues called her an "American space ninja."

She added that NASA was critical to testing theories, and laying a blueprint that SpaceX and others should follow as they endeavor to send humans to Mars, and perhaps beyond. "We need to test new techniques and make sure they're going to work," she added.