The ways in which composite materials react to radiation in space are incredibly complicated. These materials’ interactions with space radiation have damaged spacecraft components in the past, and engineers must pay careful attention to the effects of radiation on composite materials.
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How is Radiation Different in Space?
Space radiation is not the same as the radiation we commonly experience on Earth, including X-rays or gamma rays. Instead, space radiation is made up of atoms whose electrons have been stripped away while the atom was speeding through interstellar space close to the speed of light. This ultimately leaves only the atoms’ nuclei intact.
There are three discrete types of radiation in space:
- Particles that have become stuck in Earth’s magnetic field;
- Particles that were emitted into space as a result of solar flares;
- And galactic cosmic rays (these are high-energy protons and heavy ions that come from outside of our solar system).
Each type of space radiation is a kind of ionizing radiation.
Ionizing radiation loses energy as it travels through materials like spacecraft and astronauts’ bodies, and this energy is absorbed into the material it passes through. For living space travelers, the ionization of water and other components of organic cells can damage DNA molecules. This can break DNA strands and lead to long-term health problems.
There is also a secondary effect of space radiation that space engineers need to take into account: more particles including neurons can be produced when space radiation interacts with materials on the spacecraft.
Spacecraft that operate in or outside the Van Allen belts receive much more radiation than spacecraft in low Earth orbit (LEO). This far into outer space, charged particle radiation and ultraviolet radiation combine to cause polymers to harden and weaken. This leads to darkening and color centers forming in windows and other optic components, and electronics failing.
Designing Composites for Space Travel
Any component that will be exposed to a space environment has to withstand all the effects of that environment. This includes the challenges of operating in a vacuum, thermal cycling between extremely high and low temperatures, plasma effects, atomic oxygen, ultraviolet radiation, and charged particle radiation.
Engineers at space agencies like NASA have been developing bespoke composites to tackle these unique challenges for decades.
When the Apollo capsule was built by NASA to put a man on the moon in the 1960s, the composites industry was only just beginning to take off, with composite materials not yet in common use.
Early composite technology was used in Apollo’s ablative heat shield. This contained Avcoat, which is an epoxy novolac resin that has silica fibers embedded in a fiberglass-phenolic honeycomb matrix. The honeycomb was bonded to the main capsule structure and the epoxy novolac resin was injected into each cell one at a time.
Since the time of the first Apollo mission, the advanced composites sector has progressed significantly. Now, composites play an important role in all space programs; they feature in all of today’s launch infrastructure, the space shuttle, satellites, space telescopes like the James Webb Space Telescope (JWST), and the International Space Station (ISS).
Modern composite materials take advantage of useful physical or chemical traits in their disparate component materials to create combinations of these traits that cannot be found in available simple materials. For example, composites combine high strength with low weight or non-corrosive properties with thermal and electrical insulation.
Composite materials are even used to shield spacecraft and their occupants from space radiation. However, the effects of space radiation on all composite materials are complex, and careful consideration needs to go into selecting and placing them to withstand the rigors of outer space.
Scientists Study the Impact of Space Radiation on Composite Materials
A recently published review paper by scientists at Egypt’s Space Sciences Laboratory, part of the National Research Institute of Astronomy and Geophysics (NRIAG), examined the effects of space radiation on composite materials. The research was published in the NRIAG’s Journal of Astronomy and Geophysics in 2022.
The study discussed the effects of space radiation on a wide range of composite materials used in space engineering today. It found that composites can undergo degradation and see their optical, thermo-physical, and mechanical properties deteriorate under space radiation.
Increasing the dose of radiation applied to composite materials can reduce the material's strength, ultimately leading to internal fractures and surface damage. Particulate radiation can reduce the material’s molecular weight, while high-energy protons can have an impact on composites’ overall durability.
The researchers concluded that, in general, the effects of space radiation on composites used for space exploration are incredibly complicated. Because of this, engineers need to carefully consider their selection and placement of composites for spacecraft such as satellites and shuttles.
There is an old saying in space engineering: when your paperwork weighs as much as your rocket, you are ready to launch. This concept applies to every part of engineering vessels and structures for space, including the use of composites.
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References and Further Reading
El-Hameed, A.M.A. (2022). Radiation effects on composite materials used in space systems: a review. NRIAG Journal of Astronomy and Geophysics. doi.org/10.1080/20909977.2022.2079902.
Finckenor, M.M. Materials for Spacecraft. [Online] NASA. Available at: https://ntrs.nasa.gov/api/citations/20160013391/downloads/20160013391.pdf
Francis, S., (2019). Composites in the race to space. [Online] Composites World. Available at: https://www.compositesworld.com/articles/composites-in-space(2)
Why Space Radiation Matters. [Online] NASA. Available at: https://www.nasa.gov/analogs/nsrl/why-space-radiation-matters