Animations from the Inspiration Mars Foundation trace the trajectory for a 501-day round trip to Mars.





Millionaire space tourist Dennis Tito's plan to send two astronauts on a 501-day flight that zooms past Mars and swings back to Earth would set plenty of precedents on the final frontier — but the most intriguing precedent might have to do with the astronauts that are to be sent: one man and one woman, preferably a married couple beyond childbearing years. We're talking about sex in space, folks.

And if that's not intriguing enough, consider this: There are already a couple of candidates for the job.

"We'll certainly throw our hat in the ring," said Taber MacCallum, who's a member of the development team for the 2018 mission that Tito has in mind.

MacCallum and his wife, Jane Poynter, were crew members together in Biosphere 2, the controversial two-year-long experiment in long-term environmental containment. They went on to become co-founders of Paragon Space Development Corp., a company specializing in life-support systems for spacecraft. Their expertise in life support is why they're involved in Tito's "Mission for America," which was officially unveiled on Wednesday at the National Press Club in Washington. But it just so happens that they also fit the profile for the trip: Poynter is about 50, and MacCallum will turn 49 on July 20, the anniversary of the Apollo 11 moon landing.

The couple won't be the only candidates in the running. "When we tell people we're proposing to send a man and a woman on a mission to Mars, as a married couple, people line up. ... That chord gets struck over and over again," MacCallum said.

Paragon Taber MacCallum and his wife, Jane Poynter, are part of the planning team for a mission to Mars in 2018. They're also potential candidates to take the trip.

MacCallum explained that Tito wants the crew on humanity's first trip to Mars to be representative of humanity, and because the current concept for the trip calls for two spacefliers, that means a man and a woman. A married couple would be ideal, MacCallum said, because of the "whole issue of companionship." MacCallum didn't refer specifically to sex, but that would presumably be part of the companionship package.

"When you're out that far, and the Earth is a tiny, blue pinpoint, you're going to need someone you can hug," Tito told Space.com. During Wednesday's briefing, Tito told reporters that he envisioned Dr. Phil giving the couple "marital advice" during the trip.

In addition to their experience with life-support systems (and with each other), MacCallum and Poynter can draw upon their experience with life in isolation during the Biosphere 2 experiment in Arizona, which lasted from 1991 to 1993. The isolation inside a two-room spacecraft for 501 days will be even deeper. Even though the Biosphere 2 crew was separated from the outside world, "we could walk out at any time," MacCallum pointed out.

That's not the only challenge: Even with radiation shielding in place, the round trip to Mars is likely to involve exposure levels higher than NASA's limits, MacCallum said. (That's why the astronauts should be beyond their childbearing years and willing to accept an increased risk of cancer.)

Then there's the exposure to the health effects of long-term weightlessness, including bone loss and muscle loss. The astronauts who fly past Mars will surpass Soviet cosmonaut Valery Polyakov's 437-day record for continuous time in microgravity, set in 1994-1995 aboard the much roomier Mir space station.

"We're definitely pushing boundaries," MacCallum said. "It's definitely going to be hard and challenging. But we can rely on elegance and simplicity."

When, where and how?

The details of the mission plan have come to light just in the past few days, but MacCallum said that Tito has been mulling over the idea for years. Tito started out as an engineer at NASA's Jet Propulsion Laboratory, helping to design trajectories for the Mariner missions to Mars in the 1970s. Then he put his math genius to work in the investment world, building California-based Wilshire Associates into a multibillion-dollar powerhouse. In 2001, he spent around $20 million of his fortune for a seat on the Russian Soyuz spacecraft traveling to and from to the International Space Station.

After his eight-day space tour, Tito got back to business. But he also started working out a trajectory that could send a spaceship directly from Earth to Mars for a fly-by within 100 miles (160 kilometers) of the Red Planet's surface, and then back to the home planet 501 days after launch. Once the spaceship was on its way, only minor course corrections would be needed. There'd be no need for undocking or redocking ... no landing ... no do-or-die engine burn for the return from Mars.

There's one big catch, though: The trip will have to be started when the planets were aligned just right. One opportunity will come in 2016. Then there's another one in 2018. After that, the next chance won't come around until 2031.

Planning for a launch in January 2018 looked particularly attractive, and not just because that could plausibly provide enough time to put the mission together. That's also a time frame when solar activity is expected to be at a minimum, reducing the level of radiation exposure. So Tito assembled a team from Paragon as well as NASA's Ames Research Center and other space ventures to flesh out the mission plan.

The plan calls for launching the two astronauts in a crew capsule with a transfer rocket stage. If the launch vehicle is powerful enough — say, the size of SpaceX's Falcon Heavy — the upper stage and the crew capsule could be launched in one go. If the rocket doesn't have that much oomph, the capsule and the upper stage could be launched separately and then linked up in Earth orbit for the push onward to Mars.

Inspiration Mars An artist's conception shows how the spacecraft for the Inspiration Mars Foundation's "Mission for America" might be configured — with a crew capsule, an inflatable module similar to the ones built by Bigelow Aerospace, and an attached upper stage that could provide radiation shielding. The actual design has not yet been set.

"We only need to attach the upper stage. There's no need to get rid of it," MacCallum said. In the right configuration, that upper stage could even provide some of the required shielding from solar radiation and heating, he said.

The crew's 600 cubic feet of living space would include a capsule for launch and re-entry, with a well-shielded sleeping quarters that could provide a safe haven if solar storms erupted. There would be a habitat module — perhaps an inflatable module like the one that Bigelow Aerospace has been working on for NASA's use. The main idea is to keep the crew compartment as simple as possible while providing all the necessary amenities for a 501-day trip. "It's a '55 Chevy," MacCallum said.

To test the feasibility of the plan, Tito and his colleagues looked at the specifications for the Falcon Heavy as well as a modified version of SpaceX's Dragon capsule. But MacCallum emphasized that the team was not committed to using SpaceX hardware. He said the idea was getting a "great response" from a variety of aerospace companies. "If this mission is going to happen, they want 'their vehicle' to do it," McCallum said.

How much? And why?

MacCallum characterized the mission as "purely philanthropic," with the aim of inspiring future scientists and engineers as well as bridging the gap in NASA's plans for exploration beyond Earth orbit. NASA's current timetable calls for astronauts to go no farther than the International Space Station until 2021 at the earliest. Even though the Mars-and-back mission wouldn't make any stops, the trip could produce useful scientific data — and an adventure as grand as the Apollo moonshots of the '60s and '70s.

"I think we really need what Apollo did for America, but we didn't realize it while we were doing Apollo," MacCallum said.

Toward that end, Tito set up the Inspiration Mars Foundation. "He has committed to funding the first two years of this development, and he is committed to finding the rest of the money," MacCallum said. "Dennis is already getting tremendous interest in this mission from people of means."

The foundation is also looking into media deals and sponsorships. "Farmers Insurance cut a $700 million deal for the naming rights for a stadium," MacCallum noted. "Wow ... that's a not-insubstantial part of the money that we're talking about."

How much money are we talking about? MacCallum quoted Tito as saying "it's a fraction of what Curiosity cost," with reference to NASA's $2.5 billion robotic mission to Mars. Other reports have put the cost in the range of $1 billion or so — which is far less than the projected price tag for the crewed missions NASA plans to send to Mars in the 2030s.

MacCallum emphasized that Tito's "Mission for America" was meant to support America's space agency, not compete with it. "This mission is only even remotely contemplatable because of all the work that NASA has done on the International Space Station," he said. And NASA is getting something in return: MacCallum said Inspiration Mars is paying NASA for access to thermal protection technologies developed by the space agency.

Even if MacCallum and Poynter aren't picked to go on the flight, it sounds as if they'll be having the adventure of their lives over the next five years. "I feel so thrilled every day to be working with these people," MacCallum said. "It's just fabulous."

More about sex, Mars and spaceflight:

Is Dennis Tito's idea crazy? Check out this follow-up posting for a reality check.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.