The astronauts selected for an ambitious voyage to Mars could wind up looking out for No. 1 through the clever, if stomach-churning, use of No. 2.

Exposure to radiation from cosmic rays is a big concern for the Inspiration Mars Foundation team planning the 2018 Inspiration Mars mission announced last week. But they've got a possible solutionhave the two-person crew use their own feces to help block the harmful rays.

"It's a little queasy sounding, but there's no place for that material to go, and it makes great radiation shielding," Taber MacCallum, the Inspiration Mars Foundation's chief technology officer, told New Scientist recently.

Solid and liquid human waste, as well as food and water, could be stored in bags used to line the Mars capsule, MacCallum told the magazine. It turns out that a liquid like water is a better shield than metal because it's got more nuclei per volume, the key to blocking cosmic radiation.

If the thought of being surrounded by your own poop doesn't make you squeamish, there's another waste-related tidbit that mightInspiration Mars crewmembers will likely be reclaiming drinking water from their own excretions.

"Dehydrate them as much as possible, because we need to get the water back. Those solid waste products get put into a bag, put right back against the wall," MacCallum told New Scientist, adding that the Inspiration Mars spacecraft would have an external water tank for added radiation shielding.

Pioneering space tourist Dennis Tito and his Inspiration Mars Foundation are aiming to undertake the first crewed, fly-by mission to Mars in 2018, preferably using a married couple to fly the spacecraft on its 501-day trip. That's far sooner than just about anybody expected and safety concernsparticularly the risk of exposure to radiation from cosmic rayshave been raised.

Radiation exposure is a big reason the team behind the mission is looking for older astronauts to take part, according to MacCallum. Astronauts in their early 50s, rather than a younger pair, are being sought because older voyagers "would be less likely to develop the cancers that radiation could bring," he said last week.

But some scientists doubted whether the mission could be undertaken so soon with such minimal safety measures in place for the crew. For one thing, urine recycling bags have proven difficult to use in zero gravity, according to New Scientist. And the Mars Inspiration crew may have no good way to protect themselves from deadly particle bursts resulting from a solar flare.

Ultimately, the Inspiration Mars Foundation's project is one "no national space agency, such as NASA, would allow," according to scientists interviewed by The Guardian.

"It's plausible, but it's an eye-wateringly uncomfortable and risky mission design. What is important here is that this is a philosophical shift in the approach to and acceptance of risk," Dr. Kevin Fong, director of the Center for Space Medicine at University College London, told the newspaper.

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