Permanent Magnets Could Shield Astronauts From Solar Storms Without Power or Cryogenics
Featured image: Artist’s concept of an Orion spacecraft with a protective magnetic field. Credit: NASA
Radiation shielding is the single biggest unresolved problem for sending humans to Mars. Current options fall into two camps, both with serious drawbacks: passive shielding (water, polyethylene, aluminum) requires prohibitive masses that the rocket equation punishes, while active superconducting magnets need continuous cryogenic cooling and constant power, introducing single-point-of-failure risk for a system that must never fail during a solar storm.
A team of Italian and German researchers has published a first-order assessment of a third path: arrays of neodymium permanent magnets that require no power, no cooling, and have no moving parts. The study, published June 30 in the journal Aerospace, demonstrates that a 1-square-meter array of 1,482 neodymium-iron-boron (NdFeB) magnets, each 3 centimeters cubed and totaling under 300 kilograms (660 pounds), can deflect approximately 20 percent of incoming protons in the 0.1 to 10 MeV energy range, the most dangerous part of a solar particle event.
“A magnetic shield designed to protect a space probe from cosmic radiation via magnetic deflection using neodymium permanent magnets,” as lead author Valerio Parisi of Sapienza University of Rome and his colleagues describe it, acts as a high-pass filter for charged particles. Low-energy protons, the ones that deliver the highest localized dose to biological tissue, get bent away. Higher-energy particles, galactic cosmic rays in the GeV range, punch through largely unaffected.
That limitation makes the system unsuitable as a primary shield against GCRs, which are continuous, omnidirectional, and carry energies that would require impractically strong fields to deflect. But for solar particle events, which are directional, sporadic, and carry the risk of acute radiation sickness, a permanent magnet screen offers a lightweight insurance policy.
The hybrid approach
The researchers position the permanent magnet array explicitly as a supplementary system in a multi-layered radiation mitigation strategy. Passive shielding handles the omnidirectional background radiation. Permanent magnets handle the occasional solar proton bursts at a fraction of the mass cost of equivalent passive shielding. Active superconducting magnets, if and when they reach sufficient technological readiness, could eventually provide full-spectrum protection.
The mass savings are the selling point. Equivalent passive shielding for the same level of solar proton protection would likely require several metric tons of polyethylene or water, a mass penalty that propagates through every stage of the rocket equation. A permanent magnet array at under 300 kilograms is cheap to launch and requires no operational overhead.
“Even some shielding is better than none at all, and there might very well be a place for permanent magnets in a hybrid system that combines all three techniques of radiation mitigation,” the authors note.
Limitations that need solving
The study is a first-order assessment, and the authors are candid about its limitations. The prototype tested a collimated proton beam in one direction, mimicking a solar particle event but not the multi-directional, mixed-spectrum environment of actual deep space. Galactic cosmic rays, which contribute the majority of long-term cancer risk on a Mars mission, are not addressed by this approach.
The question of secondary radiation is also unresolved. Protons that hit the magnet material itself could produce secondary neutrons and gamma rays, potentially increasing the local radiation dose in certain locations inside the spacecraft. Shielding against the shield, so to speak, could eat into the mass savings.
And then there is demagnetization. NdFeB magnets exposed to space radiation degrade over time. Research indicates some grades lose half their magnetic strength at approximately 4 million rad of proton exposure and are fully demagnetized at around 70 million rad. Samarium-cobalt (SmCo) magnets offer two to forty times better radiation resistance, but are more expensive and produce slightly weaker fields. The team notes that alternative magnet chemistries should be evaluated in follow-up work.
The road ahead
The next steps involve advanced Monte Carlo simulations in realistic multi-directional radiation environments, representing actual solar particle event spectra and galactic cosmic ray spectra. Beyond that, the team envisions CubeSat-scale validation experiments that could test the concept in orbit at relatively low cost.
The paper adds to a broader resurgence of interest in magnetic shielding for deep-space missions. NASA’s MAARSS (Magnet Architectures and Active Radiation Shielding Study) program has been investigating large superconducting coil designs at 1 Tesla field strength with expandable 16-meter-diameter coils. Those concepts target full-spectrum protection but require cryogenic cooling to approximately 70 Kelvin and carry the single-point-of-failure risk that a permanent magnet array avoids.
For a permanent magnet solution to be viable for a Mars mission, the research must move from analytical modeling and lab prototypes to demonstration in the relevant radiation environment. The team’s proposal for a CubeSat mission is the logical next step. If it works, permanent magnets could become one layer of a hybrid radiation defense system, quiet, passive, and always on, requiring nothing from the crew except to be there when a solar storm hits.