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It's a key problem that will need to be addressed if humans are to attempt deep-space, long-duration missions. Not only is radiation exposure a dangerous health risk to humans, but it also poses a hazard to equipment and operating systems. Now, a team at Ghent University in Belgium are testing a possible solution: 3D printed hydrogels, which could provide deformable layers of water-filled protection.

Water acts as a great radiation shield. Relatively dense, the hydrogen-laden H₂O molecule can slow down radiation particles as they zip past. Plus, water is something that astronauts will have to bring lots of on deep space missions. We have our own built-in water shielding on Earth with the atmosphere above, with the added benefit of the Earth's magnetic field beyond.

Exposure sources are mainly two types: space weather (from the sun) and cosmic (from outside the solar system) from ancient and exotic sources, such as supernovae explosions. The 11-year solar cycle intensifies solar activity, while we see an uptick in cosmic radiation when our sun is at a lull.

Radiation exposure on the ISS

From the earliest days of the Space Age, astronauts have reported seeing occasional flashes in their eyes… even when closed. We now know this is due to high energy particles zipping through and interacting with the aqueous and vitreous humors (fluids) in the eye, and (somewhat disturbing to think about) the brain. Astronauts in low Earth orbit aboard the ISS have sheltered from solar storms in the past, taking advantage of the core modules which are at least surrounded by the bulk of the station.

But as far as providing personal protection, water poses a challenge. Bulky suits can limit movement and spring a leak: a bad thing to have happen in space. Super-absorbent polymers (SAPs) designed by the Chemistry and Biomaterials Group (PBM) at Ghent University could function as an alternative, and are more effective versus circulating water.

Enter hydrogel

SAP can absorb a hundred times its weight in liquid. This makes it an ideal lightweight and portable material to work with. Think of the "monster toys" that expand in size: just add water. Unlike traditional circulation systems, the water in hydrogel is not free-flowing, making it resistant to leakage during a puncture.

"The beauty of this project is that we are working with a well-known technology," says Lenny Van Daele (Ghent University) in a recent press release. "Hydrogels are found in many things we use every day."

Hydrogels are common in consumer products, including soft contact lenses, bio-materials, and medical bandage gels.

"The super-absorbent polymer that we are using can be processed using multiple techniques, which is a rare and advantageous quality among polymers," says Manon Minsart (Ghent University) in the same ESA press release. "Our method of choice is 3D printing, which allows us to create a hydrogel in almost any shape we want."

Radiation exposure en route to Mars

The problem posed by space radiation on long duration missions cannot be overstated. It's something that will have to be solved, if humans are to make the long round trip journey to Mars.

Curiosity's RAD experiment carried on its journey to the Red Planet in 2012 demonstrated the magnitude of the dilemma. Astronauts on a Mars mission would receive 60 rem/0.6 Sieverts… about a career's-worth of acceptable radiation exposure, in one mission.

The problem is far from solved, but hydrogels may provide a solution in the years to come. It will be exciting to see hydrogels used as a common feature on future deep space missions, to keep astronauts and equipment safe.