Millionaire space tourist Dennis Tito has a vision to send two Americans to Mars on a high-risk, budget-class, 501-day journey that would — if achieved — smash the barrier to deep space.

The proposed passengers are a middle-aged married couple, handy with tools and not prone to claustrophobia.

The Inspiration Mars Mission for America would launch, by necessity of orbital mechanics, on Jan. 5, 2018.

There is no spaceship yet, and little notion of a budget. There is no funding beyond a two-year research and development commitment by Tito. But the wealthy former rocket scientist and financier has assembled a team of credentialed advisers and plotted a mission that teeters, outside experts say, on the edge of credibility.

“It’s about inspiring the children,” Tito said at a news conference Wednesday to announce the scheme.

A timeline of the Mars rover Curiosity through its two-year mission on Mars.

Moments earlier, the onetime flier to the international space station — he paid $20 million to go there in 2001 — had lambasted what he characterized as a four-decade stagnation in the U.S. human spaceflight program.

Three years ago, President Obama touted a possible NASA Mars landing in the mid-2030s.

“I’ll be 95 years old,” Tito said. “I don’t want to wait until that time.”

But there will be no landing on Tito’s mission. No footprints and flags in ruddy soil, no rock-grabbing, no search for Martian life.

Eight months after launch, Mars will loom, then vanish in the rearview mirror.

Tito said he will sell media rights. The Mission for America might become the Red Bull Mission to Mars, the Cool Ranch Doritos Mars Shot.

“I can imagine Dr. Phil talking to this couple and solving their marital problems,” Tito said.

The nearly 18-month trip will cover 818 million miles.

Time spent within 60,000 miles of Mars: 10 hours.

Time spent pining for a bath: a seeming eternity.

“It’s not nuts,” said Taber MacCallum, chief executive of Paragon Space Development of Tucson, which is engineering the life support systems for the flight. “This is possible.”

A celestial harmony makes such a plan feasible — a once-every-15-years alignment of Earth and Mars wherein a modest craft can shoot there and back with minimal fuel.

Tito won’t fly. He’s 72. But MacCallum, 48, and his wife, Jayne Poynter, 50, offered themselves as candidates for the most grueling marriage test ever conceived.

Two decades ago, the pair spent two years inside Biosphere2, the steel-and-glass sci-fi cathedral in Arizona conceived in part as a simulated space colony.

“We used to sit inside the Biosphere and just sort of fantasize about going to Mars,” Poynter said. “Oh yeah, we did.”

The risks of this mission soar beyond those NASA would allow, said Tito adviser Jonathan Clark, a former NASA space doctor now at the Baylor College of Medicine.

Beyond low Earth orbit, cosmic radiation rises dramatically, upping the risk of cancer. If illness or injury occur, there is no hospital for millions of miles, no chance to abort, and no escape.

Because radiation can damage sperm and eggs, Tito decided the world’s first Martians should be older than reproductive age.

The new face of space travel will be wrinkled.

Other risks include missing a small “keyhole” in space near Mars and slingshotting to infinity, or vaporizing above Earth upon the fastest atmospheric reentry ever attempted.

Tito said a burgeoning new American space industry is on board. But this is, for now, largely a paper mission. NASA engineers are working on a heat shield. Paragon is building urine recycling and air purification systems. The life support apparatus will be kept simple, non-automated, and easily wrenched back to working order. There will be fecal sacks to change out, bulkheads to scrub. And plenty of time for both.

“A lot of this stuff is kind of MacGyvered,” said Clark, a reference to the late-’80s-early-’90s TV hero who fixed problems with chewing gum and paper clips.

The required hardware includes a capsule for launching and landing, a habitat module, and a big rocket — or multiple small ones. Tito said several companies are in the running to build the components in time for the brief launch window.

While NASA is not funding the mission, Tito has briefed agency leadership.

“NASA will continue discussions with Inspiration Mars to see how the agency might collaborate on mutually beneficial activities,” said NASA spokesman David Weaver.

This week, a boy who had heard about the project sent Tito — a fabulously wealthy man — $10.

“If you have a billion or two dollars, it’s technically feasible,” said Robert Zubrin, president of the Mars Society and a longtime proponent of colonizing that planet. “My main point of skepticism is not technical. It’s, ‘Do these guys have a billion dollars?’ ”

They apparently do not. Tito did not crack the Forbes 500 billionaires list, and on Wednesday he shook a digital tin cup to begin fundraising for this “philanthropic” flight. The Inspiration Mars Foundation is in talks with the National Geographic Society and the Challenger Center for Space Science Education to bring the mission into classrooms and otherwise broadcast it.

“Imagine a 13-year-old girl and her classmates getting tweets from a female astronaut at Mars,” Poynter said.

The mission — if Tito can pull it off — would reshuffle the possibilities for human space travel. Zubrin likened it to Charles Lindbergh’s first flight across the Atlantic. “It breaks the mental cage that we cannot go interplanetary until we have miraculous new propulsion,” he said.

The last time humans sailed beyond Earth orbit was the final Apollo moon mission in 1972. That was the final act of the Cold War space race.

The goal then, funded by tax dollars: beating the Soviets.

The goal now, funded by donations: beating burgeoning space power China.

“Wouldn’t I want to do that?” Tito said when asked if besting China motivated his plan. “Wouldn’t I want America to do that?”