Chris Hadfield, a former astronaut, recently spoke to Business Insider about his new online course on space exploration.

Of the future space vehicles of NASA, SpaceX, and Blue Origin, Hadfield said, "I don't think any of those three rockets is taking people to Mars."

Hadfield said we'd need some "outlandish" new space-travel technologies if we want to get to and from Mars practically.

Chris Hadfield, perhaps most widely known for his zero-gravity guitar playing, has seen an impressive amount of space travel.

Between his first spaceflight in 1995, his second in 2001, and a third in 2013, Hadfield has flown inside NASA space shuttles, a Russian Soyuz spacecraft, and the International Space Station.

Hadfield, who's now retired, shares his expertise about rockets, spaceships, spacewalking, and Mars exploration in a new web course on the online platform MasterClass.

To follow up on those lessons, we asked Hadfield what he thinks about the future rocket ships of three major players in the new space race: NASA's Space Launch System, SpaceX's Big Falcon Rocket, and Blue Origin's New Glenn rocket.

His response isn't encouraging to those who'd like to see boots on Martian ground within the next decade or two, let alone have people settle on the red planet.

"Personally, I don't think any of those three rockets is taking people to Mars," Hadfield told Business Insider. "I don't think those are a practical way to send people to Mars because they're dangerous and it takes too long."

'The majority of the astronauts that we send on those missions wouldn't make it'

A scene from "The Martian," a blockbuster sci-fi movie about an astronaut stranded on Mars. Courtesy Twentieth Century Fox

Hadfield's stance stems from the fact that all three rocket systems rely on similar fuels (plus oxygen) to lift off Earth and propel the ship through space.

"My guess is we will never go to Mars with the engines that exist on any of those three rockets unless we truly have to," he said.

NASA's Space Launch System, expected to debut in the 2020s, will power its engines with a combination of liquid hydrogen and solid chemical fuels. Blue Origin, the rocket company founded by Jeff Bezos, is also looking to use liquid hydrogen. SpaceX, founded by Elon Musk, is staking its future on burning liquid methane, which the company believes it can generate on the Martian surface.

Like other experts, Hadfield doesn't doubt that any of the vehicles could actually get to Mars — his issue is with the safety of any humans on board. Explosions, radiation, starvation, and other problems would constantly threaten a mission.

"We could send people to Mars, and decades ago — I mean, the technology that took us to the moon and back when I was just a kid, that technology can take us to Mars, but it would be at significant risk," he said. "The majority of the astronauts that we send on those missions wouldn't make it; they'd die. Because the technology is still quite primitive."

Rocket makers aren't unaware of the challenges. NASA was founded with the understanding that spaceflight is an inherently risky enterprise, and it has lived through painful examples. And Musk has repeatedly said people will probably die on his company's future voyages to Mars.

"The first journey to Mars is going to be really very dangerous," Musk said in 2016. "The risk of fatality will be high. There's just no way around it."

But Hadfield believes those risks mean we should instead be patient and slowly build up to the goal of putting humans on Mars.

"You really have to answer the question why," he said. "Why are we going? Why wouldn't we just send robots for quite a while until we learn a lot more about Mars?"

Crossing the vast ocean between Earth and Mars

Reusable spaceships might enable SpaceX to colonize Mars. SpaceX/YouTube

Hadfield said the rocket ships in development would be key stepping stones in the quest to explore our solar system.

But he added that using those vessels to shuttle people 140 million miles to Mars, even with new materials and computer automation, would be akin to crossing a giant ocean in a canoe or paddle boat.

"We're sort of like those early sailing ships in that we don't even know what we don't know yet," he said, referring to the historic voyages of Christopher Columbus, Ferdinand Magellan, and James Cook. "I think we need some more improvements in technology before we'll cross the oceans that are between us and Mars in any sort of practical way."

Hadfield said he didn't know what those technologies might be, though he noted the recent advancements in ion propulsion and NASA's resurgent interest in nuclear reactors. There could even one day be breakthroughs in investigations of dark matter and dark energy that would help this effort.

"Maybe the work that's going on with the Alpha Magnetic Spectrometer on the space station and in the particle accelerator in CERN and other places ... is going to show us how we can harness gravity," he said. "It sounds outlandish, but we figured out how to harness electricity and what electrons do, and that seemed crazy, and it's revolutionized life and travel. So who knows?"

Dana Varinsky contributed to this report.