Space Radiation: Risks to Human Health
As humanity ventures farther from Earth, the dangers posed by space radiation become increasingly urgent. Beyond the protective shield of Earth’s magnetic field, astronauts face a barrage of high-energy particles capable of ionizing atoms and inflicting substantial harm on biological tissues (NASA 2025). This exposure is considered one of the most significant barriers to long-duration, deep-space missions.
What is space radiation?
Ionizing radiation refers to particles and electromagnetic waves with enough energy to ionize atoms and molecules that it passes through, altering or breaking molecular bonds (CCOHS 2025). In space, the three major types of ionizing radiation that astronauts are exposed to include galactic cosmic radiation (GCR), solar particles, and Van Allen belt particles (NASA 2025).
Galactic cosmic radiation (GCR) consists of high-energy, high-mass atomic nuclei, often originating from supernova explosions outside our solar system (NASA 2025). These particles travel at nearly the speed of light and are extremely difficult to shield against. Due to their high mass and energy, these particles can pass through spacecraft hulls and human bodies, ionizing atoms along the way.
Solar particle events involve the ejection of mostly low- to medium-energy protons from the Sun during solar flares and coronal mass ejections (Nicogossian et al. 2016). These are sporadic and unpredictable, which make them all the more dangerous. While spacecraft shielding protects astronauts from most of these particles, those conducting spacewalks remain vulnerable if a solar event occurs unexpectedly.
Closer to Earth, the Van Allen belts are zones of trapped charged particles held in place by the Earth’s magnetic field (NASA 2023). The inner belt contains protons with energies above 100 MeV and electrons with energies over 100 KeV (Nicogossian et al. 2016). These energy levels are high enough to penetrate electronic systems and biological tissue, making them particularly dangerous during extended exposure. Past missions, such as the Apollo missions, minimized exposure by moving through these belts quickly. For comparison, the maximum radiation dose received by passing through the belts on the shortest path is roughly equal to one CT scan.
How does space radiation affect astronaut health?
Radiation in space harms biological tissue by delivering excess energy as it passes through the body (Nicogossian et al. 2016). This causes two types of damage. Direct damage involves breaking DNA strands or disrupting their structure, leading to mutations or cell death. Indirect damage occurs when radiation interacts with water in the body, generating free radicals. These unstable molecules can harm surrounding cells and DNA.
Molecular and cellular disruptions due to radiation exposure can lead to a range of short- and long-term health consequences for astronauts. The risks are typically grouped into two categories: deterministic effects and stochastic effects (Versant Physics 2021). Deterministic effects have a known dose threshold and become more severe with greater exposure. They include impaired blood cell formation, central nervous system disruption, vision impairment, and acute radiation sickness. Stochastic effects are unpredictable and can occur even with low doses of radiation. These include increased risks of cancer and heritable genetic mutations that may not appear until years after exposure.
How do we protect astronauts from space radiation?
Protecting astronauts from the effects of space radiation involves a combination of shielding, mission planning, and medical strategies (Montesinos et al. 2021). Spacecraft and space station modules are lined with shielding materials that can absorb high amounts of energy. On the ISS, sleeping quarters are shielded with hydrogen-rich polyethylene, which can reduce radiation exposure by about 20%. In addition to shielding, careful mission planning helps crews avoid solar storms and spend less time in high-radiation regions like the Van Allen belts. Astronauts may also take radioprotective drugs before radiation exposure, which help limit cellular damage. If exposure does occur, supportive treatments such as IV fluids, antibiotics, and immune boosters can help the body recover and prevent complications.
Space radiation is one of the biggest hurdles to deep space travel. Understanding and managing these invisible dangers is crucial for keeping astronauts healthy on long missions. With ongoing research and innovation, we are steadily paving the way for safer journeys into deep space.
References
Government of Canada, Canadian Centre for Occupational Health and Safety. 2025. “CCOHS: Radiation - Quantities and Units of Ionizing Radiation.” June 24. https://www.ccohs.ca/oshanswers/phys_agents/ionizing.html.
Montesinos, Carlos A., Radina Khalid, Octav Cristea, et al. 2021. “Space Radiation Protection Countermeasures in Microgravity and Planetary Exploration.” Life 11 (8): 829. https://doi.org/10.3390/life11080829.
NASA. 2017. Why Space Radiation Matters - NASA. Analog Field Testing. April 13. https://www.nasa.gov/missions/analog-field-testing/why-space-radiation-matters/.
NASA. 2023. What Are the Van Allen Belts and Why Do They Matter? - NASA Science. Biological & Physical Sciences. February 10. https://science.nasa.gov/biological-physical/stories/van-allen-belts/.
Nicogossian, Arnauld E., and James Fletcher Parker. 1982. Space Physiology and Medicine. National Aeronautics and Space Administration Scientific and Technical Information Branch.
Physics, Versant. 2021. “Deterministic vs. Stochastic Effects: What Are the Differences?” Versant Medical Physics and Radiation Safety, April 21. https://www.versantphysics.com/2021/04/21/deterministic-vs-stochastic-effects/.
