Daniel Nasaw and Andy Duckworth in Washington
It is often described as "the final frontier", and not just by those who follow the adventures of Captain Kirk and the crew of the USS Enterprise. The phrase, though, may take an even more literal meaning for those exploring space in the future.
The next generation of astronauts may hurtle through the cosmos for years or decades on a mission to explore distant planets and stars – and never return.
A senior Nasa official has told the Guardian that the world's space agencies, or the commercial firms that may eventually succeed them, could issue one-way tickets to space, with the travellers accepting that they would not come back.
The prospect of spending years cooped in a spacecraft would not deter people from applying, he said.
"You would find no shortage of volunteers," said John Olson, Nasa's director of exploration systems integration. "It's really no different than the pioneering spirit of many in past history, who took the one-way trip across the ocean, or the trip out west across the United States with no intention of ever returning."
In May 1961, President John F Kennedy challenged the US to put a man on the moon by the end of the decade and return him safely to Earth. In an effort costing an estimated $1.4tn in 2009 dollars, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin became the first humans to set foot on the moon 40 years ago today. Now, Nasa hopes to reignite the public's interest in manned space flight and win support for a massive investment in new trips to space.
If, as Olson predicts, humans reach Mars by the middle of this century, engineers and astronauts may then set their sights on the frozen planets, fiery moons and stars beyond.
"We're going back to the moon, not for flags and footsteps but for a sustained presence," Olson said. "We're going to use the moon as a stepping stone to Mars and we're going to look at other interesting spots, like asteroids and near-Earth objects, and we're going to look at all the other exciting places to go in this solar system."
Since Kennedy's speech, the US has lost 17 astronauts. Three perished in a fire during early testing for the Apollo programme and 14 died in the wreckage of the space shuttles Challenger and Columbia. In 1970, Nasa engineers saved three astronauts when Apollo 13 malfunctioned 200,000 miles from Earth. But no US astronaut has ever suffered the slow oxygen starvation and freeze that would doom a spacecraft lost beyond the Earth's orbit.
Nasa is currently bound by Kennedy's directive to bring its astronauts home, Olson said. But the other nations rapidly developing space programmes may shed the constraint, as could the commercial companies that may supplant national efforts. "Space is no longer for power and prestige; it's truly for economic benefit," the Apollo 11 flight director Eugene Kranz said. "The technology that emerges from high-risk, high-profile, extremely difficult missions is the technology that will keep the economic engine of our nation continuing to go through the years."
With currently foreseeable technology, a round trip to Mars launched from a lunar outpost would take two to three years – a journey of six to nine months each way and a year-long mission on the surface.
The star nearest Earth's solar system, Alpha Centauri, is 4.37 light years away, or more than 2.5tn miles, and a round-trip spacecraft would have to carry enough fuel to brake and propel itself back to Earth.
Robert Park, a physicist and prominent critic of manned space flight, said that even a one-way trip to Alpha Centauri was beyond the laws of physics.
The energy required to push a spacecraft up to the speed needed to get to the star within 50 years was so great as to be barely conceivable. He described the measurement as a fantastic multiple of the energy consumed by the entire world in a year.
"We don't have a warp drive," he said, referring to the interstellar engines of Star Trek fantasy. "A multigenerational space ark would doom the children raised to continue the mission never to see Earth and would decide their destiny before their birth, raising profound ethical questions."
Rather than devote immeasurable resources to sending humans into space, Park said science should instead build stronger telescopes to better study distant stars and planets.
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