Mass-Minimized Lunar Radiation Protection Using In Situ Regolith and Distributed Magnetic Shielding: Physics, Engineering Feasibility, and a Specification for Dose Validation

We evaluate a distributed superconducting perimeter fence for lunar surface protection against solar energetic particle (SEP) events. A relativistic Boris-pusher simulation shows that a 22-coil, two-channel fence attenuates SEP protons as effectively as a monolithic dipole of equal magnetic moment (94.9% versus 95.1% proton number-fluence removal; 75.4% versus 72.2% energy-fluence removal for a representative soft SEP spectrum), while leaving the protected volume field-free and avoiding a single point of failure. We then address two questions that determine buildability. First, permanent magnets are ruled out as a primary moment source: NdFeB's remanence bounds achievable moment-per-mass roughly four orders of magnitude below the superconducting design, requiring approximately 2.65×105 t of material to match the design moment. Second, propagating previously uncosted engineering margins (current derating, structural/cryostat overhead, thermal cycling, dust mitigation) gives a credible system mass of median 81 t (90% CI 55–116 t); substituting regolith-derived structure for Earth-launched structural mass reduces this to 46.4 t at unchanged attenuation. We add first-order feasibility estimates for launch, cooling, and power, plus a dose-context section situating energy-fluence attenuation against NASA dose limits and published benchmarks (regolith cladding, the AstroRad vest). These fluence-based results establish mass and attenuation feasibility but not dose reduction; we specify the coupled HZETRN2020/Geant4 transport calculation required to close that gap. The central architectural finding is that the optimal lunar SEP-mitigation strategy is asset-dependent: regolith cladding is more mass-efficient for fixed equipment, while the fence's durable role is protecting rovers, EVA crew, and distributed infrastructure that regolith cannot reach. Plain Language Summary A burst of energetic particles from the Sun can be dangerous to astronauts and equipment on the Moon’s surface, where there is no atmosphere or global magnetic field for protection. One proposed defense is a ring of superconducting magnetic coils around a work site — a “magnetic fence” — that deflects incoming particles, similar to how Earth's own magnetic field protects us from the solar wind. An earlier study by the author showed this fence shields about as well as a single large magnet at the habitat, but only roughly estimated how much material it would take to build and launch from Earth and did not connect that shielding to how much radiation a person or a piece of equipment would actually receive. This paper folds earlier physics analysis into a single, complete study and adds three new contributions. First, it checks the mass estimate more carefully and looks for ways to reduce it: ordinary permanent magnets cannot replace the coils' superconducting wire, since they are tens of thousands of times too weak per unit of mass, and building the fence's support structure from lunar soil instead of shipping it from Earth cuts the Earth-launched mass from approximately 81 tonnes to approximately 46 tonnes. Second, it adds a first-order look at the practical engineering problems of actually running such a system on the Moon—how much electrical power the cryogenic cooling would need, how large the radiators would have to be, and how the mass figures compare with what a large future rocket such as Starship could plausibly deliver to the lunar surface. Third, it connects the shielding numbers to what they mean for a person or a piece of electronics by comparing the concept with current approaches such as a few centimeters of soil cover, a water-filled protective vest, or a temporary storm shelter, each of which has published dose-reduction figures from real missions or measurements. The central finding remains that no single technology is best everywhere. For equipment that remains in one place, simply piling on 2 cm of lunar soil blocks more than 90% of the particle energy using almost no Earth-launched material, which is more efficient than the fence. The real value of the fence is to protect things that soil cannot cover, such as rovers and astronauts working outside, and the ISRU-built version of the fence makes that protection less expensive in Earth-launch terms without changing how well it shields.