If I were to ask you to list the biggest obstacles to sending humans to Mars, you would quickly point out the obvious ones: carrying enough food and water for the long journey, designing powerful rockets and spacecraft necessary to escape Earth's orbit, and the tremendous financial investment required to bring the mission to life. However, would you consider one of the greatest challenges, which also happens to be invisible? Once astronauts leave the protection of Earth’s magnetic field, they are continuously bombarded by extremely high-energy particles known as space radiation. Primarily produced by the Sun and other distant cosmic sources, space radiation poses a significant challenge for engineers designing future deep-space missions.
These high-energy particles can cause serious harm to astronauts, including cancer and tissue damage [11]. Radiation threatens far more than life on board, too. When particles strike electronic components on the spacecraft, they can cause unintended changes to a computer’s memory, known as a single-event upset (SEU) [2]. These SEUs can corrupt science data, cause navigation errors, produce incorrect calculations, and more. Over time, this radiation also degrades the spacecraft’s physical properties, increasing the likelihood of future mission failure and decreasing mission lifetime[1]. These issues are not just inherent to space exploration missions. Modern-day satellites are used for a variety of purposes (GPS navigation, weather forecasting, communication, scientific research, national security, etc.), making reliable radiation protection an essential requirement for the services humanity relies on every day. As national governments and private companies around the world continue to invest billions into satellites and potential deep-space missions, developing superior radiation protection has become an urgent engineering challenge.
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Figure 1. Earth's magnetosphere (gray) deflects much of the incoming solar wind and charged particles, providing natural protection for spacecraft in low Earth orbit. Spacecraft traveling to Mars leave this protective magnetic bubble and become exposed to the harsher deep-space radiation environment. Adapted from NASA/JPL. |
For decades, spacecraft engineers relied on aluminum as the standard material for structure and radiation shielding. Aluminum is a popular choice because it has strong mechanical properties, provides sufficient radiation protection for spacecraft operating near Earth, and can serve as the spacecraft’s frame. In fact, one of NASA’s most iconic satellites, the Hubble Space Telescope, uses aluminum as a line of defense against radiation [13]. However, Hubble is in a low Earth orbit (LEO), meaning much of its radiation protection is already provided by Earth’s magnetic field. So a potential mission to Mars, which travels far beyond the natural protection this planet provides, will require far more effective radiation shielding. Additionally, every kilogram launched into space makes the mission substantially more expensive [6], so simply throwing on more shielding isn’t feasible. A potential solution must, 1) be highly effective at deflecting radiation, and 2) be lightweight. Surprisingly, the answer to this conundrum is a material that isn’t metal at all–it may be plastic! Recent studies indicate that hydrogen-rich polymer composites can shield astronauts and spacecraft from space radiation more effectively per unit of mass than an aluminum counterpart [2] [5] [8]. These findings raise an interesting question: As space exploration reaches new frontiers, is it time to rethink the materials that protect our spacecraft?
Why Stronger Isn't Necessarily Better
At first glance, the idea seems almost impossible. After all, metals are stronger, denser, and far more durable than plastics. So, how could a plastic material possibly be able to provide better protection in one of the harshest environments known to mankind? The answer comes down to chemistry. Radiation shielding matters less about a material’s structural integrity and more about its molecular interaction with radiation on an atomic level.
Space radiation is comprised of tiny, high-energy particles traveling at blistering speeds. When these particles collide with a radiation shield, they do not just stop upon impact. Instead, they interact with the material’s atoms as they continue to penetrate, producing additional particles that then also continue to travel through the shield. This process, called secondary radiation, poses additional risks to life and electronics on board, in addition to the original particles [2] [5]. As a result, an effective shield must not only completely absorb the original radiation particles but also minimize the number of secondary particles generated in the process.
This is why chemistry becomes more important than strength, and why engineers should rethink how they evaluate shield materials. Recent findings suggest that materials composed of lighter elements generally produce fewer of these secondary particles than those composed of heavier elements [2] [3]. Hydrogen, the lightest element, is highly effective and a key ingredient in many known materials currently under test [4] [7]. Conversely, aluminum is a rather heavy material, and is more likely to create secondary particles that further harm the spacecraft [2][5].
One material with a natural abundance of hydrogen is polyethylene, a common plastic used in everyday life, such as food containers and water pipes. In a recent study, researchers simulated galactic cosmic rays (GCR) environments (a prominent source of deep-space radiation) and found that polyethylene provides greater radiation protection than an aluminum shield for the same mass [8]. This advantage is why hydrogen-rich polymers have become a major area of research, shifting the attention away from aluminum and toward this entirely new class of unique materials [5][9][10].
Putting Plastics to the Test
So does this actually work in practice? Multiple experiments suggest that it does. Researchers have repeatedly tested polymer-based materials in various simulated space environments. The findings have been generally consistent yet remarkably so. Collectively, these studies provide consensus that, for radiation protection, hydrogen-rich polymers clearly outperform aluminum, especially when accounting for the protection-to-mass ratio.
For example, in a 2025 review by Wang et al., the group found that borated polyethylene, a hydrogen-rich polymer, reduced proton-induced radiation damage by almost 26% compared to an aluminum shield at the same areal density [2]. Likewise, Naito et al. found that, when comparing numerous shielding materials and running Monte Carlo simulations to simulate space-like conditions, carbon-fiber reinforced plastic (CFRP) reduced the observed radiation dose by 1.9 times more effectively than aluminum [4]. Finally, in a study published in Space: Science & Technology, Cai et al. developed their own hydrogen-rich polyethylene material and compared its performance with that of a conventional aluminum shield. In their simulations, they found that polyethylene provided the same level of radiation protection while reducing the required shielding mass by up to 77% under GCR conditions [12]. Studies like these add to a growing body of evidence that corroborates that hydrogen-rich materials offer a noticeable advantage over metallic shielding.
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| Figure 2. Hydrogen-rich polyethylene composite panels developed for radiation shielding research. Adapted from Cai et al. (2022). |
The advantages of hydrogen-rich polymer-based shielding are significant because they help address a massive engineering constraint: spacecraft mass. Higher mass drastically increases mission complexity. As previously mentioned, a thicker aluminum shield isn’t feasible. Instead, hydrogen-rich polymers enable engineers to achieve greater radiation protection at a fraction of the material weight. For future missions to Mars, this saved mass can be used for other mission-critical components, such as fuel, food reserves, life-support systems, and instruments. These are all vital to a successful mission, and even a modest increase in available mass can be the deciding factor for a successful mission.
So what’s the Catch?
If hydrogen-rich polymers consistently outperform aluminum, why aren’t they already being implemented on modern spacecraft? The answer lies in one of aluminum’s greatest strengths: its structural integrity. Recall that aluminum is an industry-standard material because it acts as the spacecraft’s frame in addition to protecting it from radiation. So, even though aluminum is heavier and less effective at shielding against radiation, its 2-in-1 use case remains irreplaceable. This is the key shortcoming of polymer materials: they are structurally too weak to offer the same versatility as aluminum and are also highly flammable [10]. Additionally, according to NASA, no material currently provides the maximum of both protection and structure [9].
Clearly, polymers and aluminum come with their own advantages and limitations. While both are effective in their own situations, neither can meet the engineering requirements for a deep-space mission. This is where spacecraft engineers should change their perspective on how to solve the issue at hand. Instead of just trying to find a single material that excels in all categories, engineers should leverage hybrid composite shields that incorporate hydrogen-rich polymers for their excellent radiation protection and a heavier element, such as aluminum or carbon fiber, for the structural strength needed for longer missions [3][6][9]. The future of spacecraft shielding most likely won’t be a single material at all. Instead, as the evidence suggests, the solution will be a hybrid of materials that leverage each material's unique strengths.
Looking Ahead
Now, when I ask you about the technologies that will make missions to Mars a reality, I hope radiation shielding is one of the first things that comes to mind. Recent research suggests that an effective radiation shield is not just about finding the strongest material, but rather about understanding how different materials interact with radiation particles at the molecular level and combining their strengths into an ideal composite. For the next generation of spacecraft that aims to take on the most ambitious projects, engineers should move beyond relying solely on aluminum and transition to more sophisticated hybrid composite materials, which will be safer, lighter, and more capable for deep-space exploration.
References
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“The Impact of Space Radiation Environment on Satellites Operation in Near-Earth Space | IntechOpen.” Accessed: Jun. 13, 2026. [Online]. Available: https://www.intechopen.com/chapters/70180#
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M. Wang et al., “Review of Passive Shielding Materials for High-Energy Charged Particles in Earth’s Orbit,” Materials (Basel), vol. 18, no. 11, p. 2558, May 2025, doi: 10.3390/ma18112558.
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“Aerospace Materials Characteristics,” Progress in Astronautics and Aeronautics. Accessed: Jun. 13, 2026. [Online]. Available: https://arc.aiaa.org/doi/10.2514/5.9781624104893.0011.0208
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M. Naito et al., “Investigation of shielding material properties for effective space radiation protection,” Life Sciences in Space Research, vol. 26, pp. 69–76, Aug. 2020, doi: 10.1016/j.lssr.2020.05.001.
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E. Toto, L. Lambertini, S. Laurenzi, and M. G. Santonicola, “Recent Advances and Challenges in Polymer-Based Materials for Space Radiation Shielding,” Polymers, vol. 16, no. Compendex, 2024, doi: 10.3390/polym16030382.
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S. Guan, G. Fu, B. Wan, X. Wang, and Z. Chen, “Multi-Objective Optimization and Reliability Assessment of Multi-Layer Radiation Shielding for Deep Space Missions,” Aerospace, vol. 12, no. 4, p. 337, Apr. 2025, doi: 10.3390/aerospace12040337.
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A. Gohel and R. Makwana, “Multi-layered shielding materials for high energy space radiation,” Radiation Physics and Chemistry, vol. 197, p. 110131, Aug. 2022, doi: 10.1016/j.radphyschem.2022.110131.
[8]
S. Guetersloh et al., “Polyethylene as a radiation shielding standard in simulated cosmic-ray environments,” Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, vol. 252, no. 2, pp. 319–332, Nov. 2006, doi: 10.1016/j.nimb.2006.08.019.
[9]
“Radiation Shielding Materials Containing Hydrogen, Boron, and Nitrogen: Systematic Computational and Experimental Study - Phase I”.
https://www.nasa.gov/wp-
content/uploads/2017/07/niac_2011_phasei_thibeault_radiationshieldingmaterials_tagged.pdf
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“NASA TechPort - Project.” Accessed: Jun. 13, 2026. [Online]. Available: https://techport.nasa.gov/project
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“Evaluating shielding approaches to reduce space radiation cancer risks (NASA TM-2012-217361).,” 2012.
https://three.jsc.nasa.gov/articles/CucinottaKimChappell0512.pdf
[12]
M. Cai et al., "Experimental and Simulation Study on Shielding Performance of Developed Hydrogenous Composites," Space: Science & Technology, 2022.
[13]
“Hubble Design - NASA Science.” Accessed: Jun. 25, 2026. [Online]. Available: https://science.nasa.gov/mission/hubble/observatory/design/
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