The Role of Regolith in Protecting Astronauts from Radiation on the Moon

Protecting future astronauts from the radiation of deep space is one of the most urgent problems in human spaceflight — and the solutions are being developed in laboratories today.

One of the most serious health risks facing astronauts on the Moon is radiation. Without Earth's protective magnetic field and atmosphere, the lunar surface is exposed to a constant stream of harmful radiation from the Sun and deep space. Shielding future lunar habitats from this radiation is one of the most important engineering challenges in human spaceflight — and regolith may be the best available solution. Space Resource Technologies produces the stimulants that radiation shielding researchers use to develop and test their protective designs. The Radiation Environment on the Moon On Earth, our planet's magnetic field deflects most charged particle radiation, and the atmosphere absorbs most of what gets through. On the Moon, these protections disappear entirely. The lunar surface receives the full intensity of galactic cosmic rays — high-energy particles originating from outside our solar system — as well as solar energetic particles from solar flares and coronal mass ejections. Over a year-long lunar stay, accumulated radiation exposure would significantly exceed the lifetime occupational limits recommended for astronauts — making robust shielding essential for long-duration missions. Why Regolith is an Effective Radiation Shield The principle behind regolith radiation shielding is simple — mass stops radiation. High-energy particles lose energy as they pass through material, and enough material will stop them entirely. Regolith, being dense and abundant, is an excellent bulk shielding material. Research has shown that a layer of lunar regolith approximately two meters thick reduces radiation exposure to levels comparable to Earth's surface. This is achievable — the Moon has an unlimited supply of regolith, and robotic systems could pile it over habitat modules before astronauts arrive. Testing Shielding Effectiveness with Stimulants Measuring how effectively different regolith compositions stop radiation requires physical testing using particle accelerators or radiation sources. Researchers use regolith stimulant to create test samples of various compositions and thicknesses and then measure attenuation — how much the radiation is reduced as it passes through the material. Different stimulant compositions may have different shielding effectiveness depending on their hydrogen content and elemental composition. Hydrogen is particularly effective at stopping neutron secondary radiation, which is why water and polyethylene are often proposed as supplemental shielding materials alongside regolith. Solar Weather and Emergency Shelters Even with excellent bulk shielding, the most intense solar particle events can produce radiation spikes that exceed the protection of standard shielding. Future lunar bases will likely include a dedicated storm shelter — a smaller, highly shielded space where astronauts can retreat during solar weather events. Designing this shelter requires understanding exactly how regolith stops different types of radiation under worst-case conditions — knowledge that comes directly from experimental testing with stimulants. STEM Connections Radiation shielding connects physics, materials science, and health science in a genuinely important real-world application. For students, exploring how different materials stop different types of radiation, calculating the thickness of shielding needed to achieve a given protection level, or designing a habitat that optimizes protection against construction cost — these are rich, authentic engineering challenges. Protecting future astronauts from the radiation of deep space is one of the most urgent problems in human spaceflight — and the solutions are being developed in laboratories today.