It's usually cheaper to fly one way, even to Mars.
Two scientists are suggesting that colonization of the red planet could happen faster and more economically if astronauts behaved like the first settlers to come to North America — not expecting to go home.
"The main point is to get Mars exploration moving," said Dirk Schulze-Makuch, a Washington State University professor who co-authored an article that seriously proposes what sounds like a preposterous idea.
At least one moon-walking astronaut was not impressed.
"This is premature," Ed Mitchell of Apollo 14 wrote in an e-mail. "We aren't ready for this yet."
Also cool to the idea was NASA. President Barack Obama has already outlined a plan to go to Mars by the mid-2030s, but he never suggested these space travelers wouldn't come home.
"We want our people back," NASA spokesman Michael Braukus said.
The article titled "To Boldly Go" appears in the latest issue of the Journal of Cosmology, which featured more than 50 articles and essays on Mars exploration.
Schulze-Makuch and Paul Davies, a physicist at Arizona State University, argue that humans must begin colonizing another planet as a hedge against a catastrophe on Earth. They believe the one-way trips could start in two decades.
"You would send a little bit older folks, around 60 or something like that," Schulze-Makuch said, bringing to mind the aging heroes who saved the day in the movie "Space Cowboys."
That's because the mission would undoubtedly reduce a person's lifespan, from a lack of medical care and exposure to radiation. Radiation could also damage reproductive organs, so sending people of childbearing age is not a good idea, Schulze-Makuch said.
Mars is a six-month flight away, and it has surface gravity, a thin atmosphere, frozen water, carbon dioxide and essential minerals. The two scientists propose the missions begin with two two-person teams, in separate ships that would serve as living quarters on the planet. More colonists and regular supply ships would follow.
The technology already exists, or is within easy reach, they wrote. By not taking the extra fuel and provisions necessary for a return trip to Earth, the mission could cut costs by 80 percent.
Davies and Schulze-Makuch say it's important to realize they're not proposing a "suicide mission."
"The astronauts would go to Mars with the intention of staying for the rest of their lives, as trailblazers of a permanent human Mars colony," they wrote.
They acknowledge the proposal is a tough sell for NASA, with its focus on safety, and suggest the private sector might be more fertile ground.
"What we would need is an eccentric billionaire," Schulze-Makuch said. "There are people who have the money to put this into reality."
Indeed, British tycoon Richard Branson, PayPal founder Elon Musk and Amazon.com Inc. CEO Jeff Bezos are among the rich who are already involved in private space ventures.
Isolated humans in space have long been a staple of science fiction movies, from "Robinson Crusoe on Mars" and "2001: A Space Odyssey" to a flurry of recent movies such as "Solaris" and "Moon." In many of the plots, lonely astronauts fall victim to computers, madness or aliens.
Psychological profiling and training of the astronauts, plus constant communication with Earth, would reduce debilitating mental strains, the two scientists said.
"They would, in fact, feel more connected to home than the early Antarctic explorers," they write in their article.
The mental health of humans in space has been extensively studied. Depression can set in, people become irritated with each other, and sleep can be disrupted, studies have found. The knowledge that there is no quick return to Earth would likely make that worse.
Davies' research focuses on cosmology, quantum field theory and astrobiology. He was an early proponent of the theory that life on Earth may have come from Mars in rocks ejected by asteroid and comet impacts.
Schulze-Makuch is the author of two books about life on other planets. His focus is eco-hydrogeology, which includes the study of water on planets and moons of our solar system and how those could serve as a potential habitat for microbial life.
Both men contend that Mars has abundant resources to help the colonists become self-sufficient over time. They write that the colony should be next to a large ice cave, to provide shelter from radiation, plus water and oxygen.
Despite the lack of enthusiasm from NASA, Schulze-Makuch believes many people would be willing to make the sacrifice.
He and Davies believe a Mars base would offer humanity a "lifeboat" if Earth became uninhabitable.
"We are on a vulnerable planet," Schulze-Makuch said. "Asteroid impact can threaten us, or a supernova explosion. If we want to survive as a species, we have to expand into the solar system and likely beyond."