Man-and-woman Mars trip by 2018? Can you say 'couples counseling'?

A wealthy space tourist announced plans today to launch a high-risk manned flight to Mars in 2018, sending a man and a woman on a bare-bones 501-day round-trip flyby, passing just 100 miles above the Red Planet before heading back to Earth.

Dennis Tito, the first private citizen to fly aboard the International Space Station, said he will provide two years of funding to support the Inspiration Mars Foundation, a nonprofit he started to execute the proposed venture. Additional money will be raised from private sources.

"We have 50 years of experience," he told reporters during a news conference. "We can do things a lot faster, we just need a commitment. I'm not worried about getting this done from that standpoint. The vehicles are there, we have time to get it together."

In a statement, Tito said his organization is "engaging the best minds in industry, government, and academia to develop and integrate the space flight systems and to design innovative research, education, and outreach programs for the mission."

"This low-cost, collaborative, philanthropic approach to tackling this dynamic challenge will showcase U.S. innovation at its best and benefit all Americans in a variety of ways."

But building a reliable, affordable spacecraft in five years is just one issue facing mission planners. Spending nearly one-and-a-half years in the weightless environment of space poses a variety of health risks for the two-person crew, along with an increased risk of cancer due to the effects of space radiation.

And then there's the psychological stress associated with extended confinement in a vehicle the size of a motor home.

Homer Hickham, author or "Rocket Boys/October Sky," said in a Twitter posting: "A married couple in a bathroom for 501 days? I love my wife but rather take my cat and some good books."

He joked that a book about the trip might be titled "Murder on the Martian Express."

But Jon Clark, a former NASA flight surgeon whose wife, Laurel Clark, perished in the 2003 Columbia disaster, said exhaustive screening procedures will be used to select candidates with excellent health, technical competence, and psychological stability.

Preflight training and well-established exercise protocols will help offset the effects of prolonged exposure to microgravity, but space radiation remains a major concern. Clark said NASA will not consider a mission that could result in a 3 percent excess cancer mortality rate over a lifetime.

The proposed Mars flyby mission is "in that ballpark," said Clark, who is working with the Inspiration Mars Foundation. "So, the real issue here is understanding the risk in an informed capacity. The crew would understand that. Ultimately, that is going to be the decision based on that informed consent."

Taber MacCallum, the chief technical officer for Inspiration Mars and CEO of Paragon Space Development, said it's "the kind of risk America used to be able to take."

"That's the kind of bold thing we used to be able to do, we don't do that anymore," he said. "We've shirked away from risk. I think just seriously contemplating this mission recalibrates what we believe is a risk worth taking for America."

As for the challenge of developing a manned flyby spaceraft in just five years, MacCallum said "American industry is up to this challenge."

"There are lots of options and ways to get this done," he said. "We have an amazing industrial base and it's about time America stood up and proved to the rest of the world we've got, bar none, the best industrial base in the world. Let's show it to them. Let's do this mission."

The proposed trip would take advantage of a relatively rare alignment between Earth and Mars, allowing a spacecraft to follow a fast "free-return" trajectory.

Assuming a launch on January 5, 2018, the spacecraft could reach Mars in 228 days and simply loop around the planet, using gravity to fling it back toward Earth. The return trip would take 273 days and end with re-entry on May 21, 2019, at a record velocity of 31,000 mph.

The crew would rely on a closed-loop life-support system, recycling water, urine, and sweat using technology similar to that aboard the International Space Station.

While a specific mission architecture has not been established, the two-person crew likely will live and work in an inflatable habitat module attached to the capsule used for launch and entry. The idea is to utilize current technology with a minimum of automation, relying strongly on the crew's ability to operate the spacecraft and make repairs as needed.

Tito said a variety of launch vehicles should be available, including a proposed heavy-lift booster planned by Space Exploration Technologies, or SpaceX. The company also is working on a manned version of its Dragon cargo capsule, a variant of which might be suitable for the Mars trip.

Once on the way to Mars, the crew would not be able to abort and make a quick return to Earth if something went wrong. They would be committed to the full-duration 501-day mission.

MacCallum said mission planners are considering a 1,200-cubic-foot spacecraft, half of which would be filled with food, water, life-support equipment, and spare parts. The crew would have about 600 cubic feet of living space.

Tito did not have a realistic cost estimate, but he said he expected it to be in the range of a robotic Mars mission. NASA's twin Mars Exploration Rovers cost about $400 million each, while the more sophisticated Curiosity rover currently at work on the Red Planet cost some $2.5 billion.

"It uses low-Earth orbit architecture and we're just adapting it, in effect, to a very large Earth orbit that...just happens to go out pretty far," Tito said. "But you're really flying this mission without a propulsion system on the spacecraft, it's in the most simple form.

"Compared to, say, the landing missions, even if you could contemplate what an overall landing mission to Mars might cost or even in today's dollars what the Apollo missions cost, you're talking a factor of a hundred (less). This is really chump change."

Whatever the final price tag of the proposed manned flyby mission, Tito said he welcomed the opportunity to raise money, joking that media rights alone would be worth a fortune.

"Dr. Phil solving their marital problems, it will be great," Tito quipped.