Is the Red Planet looking particularly brown today? (Image: SpaceX/NASA)

The man and woman aboard the Inspiration Mars mission set to fly-by the Red Planet in 2018 will face cramped conditions, muscle atrophy and potential boredom. But their greatest health risk comes from exposure to the radiation from cosmic rays. The solution? Line the spacecraft’s walls with water, food and their own faeces.

“It’s a little queasy sounding, but there’s no place for that material to go, and it makes great radiation shielding,” says Taber MacCallum, a member of the team funded by multimillionaire Dennis Tito, who announced the audacious plan earlier this week.

McCallum told New Scientist that solid and liquid human waste products would get put into bags and used as a radiation shield – as well as being dehydrated so that any water can be recycled for drinking. “Dehydrate them as much as possible, because we need to get the water back,” he said. “Those solid waste products get put into a bag, put right back against the wall.”


Food too, could be used as a shield, he said. “Food is going to be stored all around the walls of the spacecraft, because food is good radiation shielding,” he said. This wouldn’t be dangerous as the food would merely be blocking the radiation, it wouldn’t become a radioactive source.

Water 1 – Metals 0

The details of Inspiration Mars’s plans have yet to be clarified, but the team has said it will be using “state-of-the-art technologies derived from NASA and the International Space Station”.

One idea that is already under consideration by the agency’s Innovative Advanced Concepts programme, which funds research into futuristic space technology, is a project called Water Walls, which combines life-support and waste-processing systems with radiation shielding.

Water has long been suggested as a shielding material for interplanetary space missions. “Water is better than metals for protection,” says Marco Durante of the Technical University of Darmstadt in Germany. That’s because nuclei are the things that block cosmic rays, and water molecules, made of three small atoms, contain more nuclei per volume than a metal.

Water shielding also has another benefit – you can drink it. Such dual use is essential aboard a spacecraft, where space is at a premium. Applying this rationale, the Water Walls concept involves polyethylene bags that use osmosis to process clean drinking water from urine and faeces.

Sights and smells

Lining the walls of a spacecraft with layers of these bags creates a 40-centimetre-thick liquid shield. All of the bags would initially be filled with drinking water. The crew would then fill other bags with waste during the trip to Mars and swap them out for the now-empty water bags.

The osmosis-based processing is much simpler than the automated life-support systems aboard the International Space Station, making it less likely to fail during the long ride to Mars.

However, there are problems to be ironed out. The urine-to-water processing bags were tested in orbit on the last ever flight of the space shuttle in 2011 and found to be 50 per cent less efficient in microgravity than in ground-based tests.

Besides testing that the various bags work properly, the Water Walls team points out the more basic worry of dealing with the residual sights and smells. MacCallum made a similar point about the system to be used on Inspiration Mars: “Hopefully they’re not clear bags,” he said.

Solar danger

Not all bags need be equally unpleasant, though. The Water Walls concept also includes bags that scrub carbon dioxide from air, regulate temperature and grow algae for food – although NASA hasn’t yet taken those to space.

Inspiration Mars also plans to have an external water tank and the aluminium skin of the spacecraft itself for extra protection. This kind of shielding should keep astronauts safe from lower energy cosmic rays, says Ruth Bamford of the Rutherford Appleton Laboratory in Didcot, UK, who is working on creating magnetic “deflector shields” for spacecraft.

Organic material or aluminium is no defence against the burst of particles that occasionally spew out from the sun during a solar storm, however. “For this, putting three metres of concrete may not be enough to protect the astronauts,” says Bamford. Inspiration Mars say they should be able to keep the upper rocket stage of their launch vehicle attached to the spacecraft for the whole of the trip, and point that towards the sun in the event of a flare.