Surviving the Journey: Protecting Astronauts from Space Radiation
The vastness of space has beckoned many an adventurer. Yet with the exception of the Apollo astronauts, all astronauts thus far have never travelled outside of Low Earth Orbit. Remaining reasonably close to Earth, they are protected by its magnetic field. To travel further out would mean facing damaging cosmic and solar radiation.
Outside the protective cocoon of the Earth’s magnetic field is a universe full of radiation. Unlike any of the radiation we encounter on Earth, space radiation consists of solar particles that burst out of the Sun at high speeds, and galactic cosmic rays that come from outside our solar system.
NASA’s Artemis Mission aims to send the first woman and next man to the Moon in 2024, but a lot of groundwork needs to first be done in order to make this a reality. Experimental physicist Dr Gail Iles works with RMIT University’s Space Science program, investigating ways to overcome the radiation barrier so that astronauts can survive long journeys, or even live indefinitely, in space.
Gail was drawn to physics because she was able to delve deep into the atomic and nuclei levels of matter, and also study gigantic things such as the entire Cosmos. Certainly, the scale of the Universe is incomprehensively gigantic. Low Earth Orbit and most satellites huddle the Earth’s atmosphere, only extending 2,000 km away. Medium Earth Orbit then spans to 36,000 km away, with GPS satellites at around the 20,000 km mark. Everything is close when compared to the Moon, however, which is 400,000 km away (and even beyond High Earth Orbit). Even then, a “magnetotail,” pushed out behind the Earth’s magnetic field by the onslaught of Solar particles, can briefly protect the path to the Moon as the Earth blocks it from the Sun.
‘The power and energy being emitted from the Sun is formidable,’ says Gail.
At the core of the Sun, 500 million metric tons of hydrogen undergoes nuclear fusion every second. This creates tremendous amounts of energy, and every now and then, large eruptions of charged particles burst out. Solar flares are often accompanied by coronal mass ejections, large expulsions of magnetised particles that shoot out at speeds of up to 3,500 km/s. The bulk of these ejections comprise of alpha particles (positive) and beta particles (negative). These can affect our communication networks and GPS satellites, and in 1989, a solar storm caused an electrical blackout across the entire Quebec Province in Canada.
An additional concern for space travel is the galactic cosmic rays that come from the rest of the Cosmos. Like solar radiation, these are classified as high-energy, ionising radiation that have enough energy to completely knock out electrons from atoms when they cross paths – essentially altering materials as they pass through. These particles can be likened to atomic-scale cannonballs that blast through material, leaving damage behind, and even creating secondary radiation particles, such as gamma rays (the highest energy particles) and neutrons (neutral) that cause further damage.
Gail’s task is to prevent these super-fast, super-charged particles from wreaking havoc on astronauts’ bodies. On the surface of the Earth, we are all subject to a natural, background dose of ionising radiation from rocks (receiving a dose of about 3 mSv per year). A full body CT scan would add an additional 10 mSv, a radiation worker would be exposed to less than 50 mSv per year as mandated by the Department of Energy’s regulations, while an astronaut on the International Space Station is exposed to 100 mSv in six months. Higher radiation doses increase a person’s risk of cancer and other illnesses, and the 180-day transit to Mars would push humans well above a limit of radiation that NASA considers acceptable.
On Earth, the solutions to radiation shielding are relatively easy (not to mention, the magnetic field that huddles our planet also provides protection). To protect against alpha particles (if they’re travelling slowly), we can use something as thin as paper or our skin. Beta particles are smaller and therefore more dense materials, such as aluminium, need to be used. Gamma rays have a higher penetrating power, therefore requiring thicker materials to block them – lead is often used in medical institutions and nuclear power plants. Neutrons are difficult to detect, but hydrogen atoms provide protection because neutrons are absorbed by their light nuclei. Hydrogen-rich materials such as water, concrete, and plastic, can therefore be used as a shield to slow them down.
The challenge with using these as protection in space is that any of these shields would need to be launched. The heavier a material is, the more fuel is needed to launch it and the more expensive it becomes to launch. Spacecraft needs to be as lightweight as possible, shield against radiation, and also be durable against potential meteors and debris. Current spacecraft have multiple bumper shields of thin aluminium sheets, a net of Kevlar and epoxy (materials high in hydrogen that are also used in military and fire-fighting gear), and air gaps in between to slow down radiation particles.
But what happens once an astronaut leaves the safety of the spacecraft and goes on a spacewalk? Spacewalks have to be limited in time and frequency to avoid excessive radiation exposure. And once we set up base on the Moon, which is covered in radiation as it has no protective shield, we would likely have to build underground.
On top of the more passive forms of shielding that simply act as barriers, there are more active forms of shielding that mimic the Earth’s magnetic field. Given that they need to be much smaller than the Earth to be portable while generating the same protection, they require an enormous amount of power. Superconducting magnets make this possible and it has been proposed that they line spacecrafts to deflect radiation particles. The problem, however, is that superconducting magnets are massive in size, heavy, and would require constant cooling with liquid nitrogen (an additional weight). Gail is researching
lightweight alternatives for active shielding that utilise the power of the spacecraft itself at RMIT University – and she has three or four years to do this in time for the Artemis Mission.
Humans are always exploring and looking for new challenges. After having been an astronaut trainer herself and having felt so comfortable in zero-gravity, Gail herself would love to get into space one day. Her work in ensuring that astronauts are shielded from radiation from the stars, as they travel to the Moon and beyond.
This article follows a presentation to the Royal Society of Victoria on 22nd April 2021 titled “Surviving the Journey: Protecting Astronauts from Space Radiation” delivered by Dr Gail Iles (RMIT University). All images used here were captured during her presentation.