StemRad vest cuts astronaut radiation dose 60% in Moon test

A wearable radiation-shielding vest flown to the Moon and back aboard NASA's uncrewed Artemis I mission would cut an astronaut's radiation dose by up to 60 percent during a solar storm, according to a study published August 13, 2026 in Science Advances. The AstroRad vest, developed by Israeli-American startup StemRad in collaboration with Lockheed Martin, performed roughly as well as the Orion spacecraft's heavily shielded onboard storm shelter, but without confining the crew to a small area.

Solar storms, such as the August 1972 event that occurred between Apollo 16 and Apollo 17, can hurl bursts of protons intense enough to raise cancer risk or cause radiation sickness. Earth's atmosphere and magnetic field absorb this radiation, but crews heading to the Moon or Mars lack that protection, and no spacecraft built so far has enough shielding to stop it. The vest addresses this by shielding the astronaut rather than the entire spacecraft, focusing on radiation-sensitive tissues like bone marrow, breasts, stomach, colon, and reproductive organs.

The vest's design uses high-density polyethylene (HDPE), a plastic that packs more hydrogen by mass than water, making it an effective shield. To maintain flexibility, engineers broke the HDPE into thousands of hexagonal rods, 9 to 60 millimeters long, sandwiched between elastic fabric layers. The rods' lengths were calculated using the Bethe-Bloch formula, which describes how charged particles lose energy in matter. The vest weighed 26 kilograms on Artemis I, roughly as much as a full suit of medieval plate armor.

Because Artemis I flew without a crew, the vest was worn by a torso phantom named Zohar, while an identical phantom, Helga, went unprotected. Both were packed with thousands of dosimeters. Most radiation recorded came from Earth's inner Van Allen belt, since no solar storm occurred during the flight. The team used the belt crossing as a proxy, building Monte Carlo simulations that matched dosimeter readings within five percent. They then modeled two historical storms: the vest cut effective dose by about 60 percent for the August 1972 event and about 40 percent for the October 1989 storm, which was more energetic.

Wearing the vest during a single major storm could extend an astronaut's career by roughly 40 to 193 days against NASA's 600-millisievert lifetime dose limit, comparable to Orion's storm shelter but allowing mobility. The vest does little against galactic cosmic rays, which arrive continuously at higher energies. StemRad has already reduced the vest's weight from 26 to 16 kilograms using Artemis I data, aiming for a lighter version wearable for days around a storm's peak. The study is published at http://dx.doi.org/10.1126/sciadv.adz1892.