The vastness of space has beckoned many an adventurer. Yet with the exception of the Apollo astronauts, no human has ever 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 dangerous cosmic and solar radiation.
Outside the protective cocoon of the Earth’s magnetic field is a universe full of damaging 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, most often produced by explosive phenomena such as supernovae. 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 be done 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. Most satellites huddle around our planet in Low Earth Orbit, only reaching 2,000 km from the Earth’s surface. Medium Earth Orbit then spans to the ring of geostationary satellites 36,000 km away (so named because they orbit the Earth at the same pace as it spins, meaning that they appear stationary above a spot on the Earth’s surface), with GPS satellites at around the 20,000 km mark. Everything is close when compared to the Moon, however, which is 385,000 km away. Even then, a “magnetotail,” pushed out behind the Earth’s magnetic field by the onslaught of solar particles, can only briefly protect the path to the Moon as the Earth blocks it from the Sun.
The neighbourhood nuclear fission reactor
‘The power and energy being emitted from the Sun is formidable,’ says Gail. At the core of the Sun, 500 million metric tonnes of hydrogen undergo 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 are positively-charged alpha particles and negatively-charged beta particles . These can affect our communication networks and GPS satellites: 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 high-energy, ionising radiation that have enough energy to completely knock electrons from atoms when they cross paths – essentially altering materials as they pass through. These particles are like atomic-scale cannonballs, damaging material as they blast through. They can even create 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. Here on Earth, we are all subject to a natural, background dose of ionising radiation (about 3 mSv per year) from rocks. 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 per industry regulations), while an astronaut on the International Space Station is exposed to 100 mSv in six months. Higher radiation doses increase the 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.
Protecting against different types of radiation
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 are travelling slowly), we can use shield materials 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 higher penetrating power, therefore requiring thicker materials to be blocked – 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 any of these as protection in space is that shields made from these materials would need to be launched. The heavier a material is, the more fuel is needed and the more expensive it becomes to launch. Spacecraft design is a delicate balance: it needs to be as lightweight as possible, shield against radiation, and be durable against potential meteors and debris. Current spacecraft have multiple bumper shields of thin aluminium sheets, a net of Kevlar and epoxy (materials rich in hydrogen that are also used in military and fire-fighting gear), and air gaps in between these layers to further 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 to establish a base on the Moon – which is covered in radiation as it has no protective magnetic shield – we would likely have to build underground in channels beneath the surface. 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 size of our entire planet to be portable while generating the same level of protection, they require an enormous amount of power. Superconducting magnets make this possible and they have been proposed as a lining for spacecraft 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. She has found that electromagnets provide a lighter weight, alternative shield capable of deflecting charged particles away from spacecraft. Humans are always exploring and looking for new challenges. After having been an astronaut trainer herself and having felt so comfortable on the “Vomit Comet”, a plane for astronauts to train for the microgravity of space, Gail would love to get into space herself one day. Her work is ensuring that astronauts are shielded from radiation from the stars, as they travel to the Moon and beyond.
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