Could a radiation vest mean the difference between life and death on a trip to Mars?

Elon Musk's SpaceX has pledged to send humans to Mars, while NASA is pushing ahead with the Artemis program — its first crewed lunar mission in 54 years — with plans to establish a base on the moon.

The moment a spacecraft leaves Earth, however, the atmosphere and magnetic field that shield us from radiation disappear. Chief among the hazards is a solar storm, which can strike with as little as a few hours' warning. A single storm on the scale of the one that occurred in October 1989 would expose an astronaut to 36.5 percent of the total radiation dose permitted over an entire career.

When the Artemis I spacecraft orbited the moon in 2022, it carried two mannequins — one wearing a radiation protection vest, one without. Researchers calculated that had a solar storm struck during the flight, the unprotected mannequin would have suffered damage to 97.9 percent of its bone marrow, a level that would be fatal. Humans need at least 2.5 percent of their bone marrow intact to survive and recover. The vested mannequin retained 5.5 percent.

Those findings were published in volume 12, issue 33 of the international journal Science Advances by a research team led by Dr. Jordan Houri and Dr. Oren Milstein of StemRad, a US company. The German Aerospace Center, the Israel Space Agency and NASA also participated in the study.

When the body absorbs a large dose of radiation at once, bone marrow is the first organ to fail. This mesh-like tissue inside bones produces blood cells.

Bone marrow can regenerate and recover if as little as 2.5 percent of the total supply remains intact — the same principle used in leukemia treatment, where the body is irradiated before a marrow transplant.

The research team based their calculations on the actual solar storm of October 1989, scaling up the radiation intensity from there. Without a vest, an astronaut's bone marrow would absorb around 6 gray (Gy) — a unit measuring how much radiation energy the body or a material absorbs. A whole-body dose of 6 Gy is a serious, life-threatening level of exposure.

When the research team ran the same test with a vested mannequin, 94.5 percent of bone marrow was still damaged — but 5.5 percent survived, just above the 5 percent clinical threshold the researchers set as their target.

The sun unpredictably erupts from time to time, unleashing torrents of protons. During such events, radiation levels can surge to 10,000 to 100,000 times their normal intensity within hours to days — and a solar storm may give only a few hours' warning at most.

On Earth, the atmosphere and magnetic field absorb that radiation. In space, the only alternative is thickening a spacecraft's outer walls, which adds weight and makes launch far more difficult.

That constraint gave rise to the idea of a vest that shields only the organs most vulnerable to radiation. The material belongs to the same family of plastics used in water bottles and cutting boards, chosen for its ability to block protons efficiently relative to its weight. The vest weighs 26 kilograms.

NASA caps the total career radiation dose for astronauts at 600 millisieverts (mSv).

A single unprotected encounter with a storm on the scale of the October 1989 event would consume 36.5 percent of that lifetime allowance in one go. Wearing the vest reduces that figure to 23.0 percent.

When background galactic radiation is factored in alongside solar storms, the vest extends the time an astronaut can safely remain in space by 40 to 193 days. The wide range reflects the fact that routine radiation levels during periods of high solar activity can be more than three times greater than during quiet periods.

The research team said the vest would prove even more useful aboard next-generation spacecraft. Vehicles with large interiors — such as SpaceX's Starship — and inflatable habitat modules have thinner walls, allowing more radiation to penetrate.

The vest is not a complete solution, however. Beyond solar radiation, astronauts on a Mars mission would also be exposed to galactic cosmic rays throughout the journey, and the vest offers no protection against that cumulative dose — it is an emergency measure to be worn only when a radiation storm strikes.

The team also acknowledged that because no actual solar storm occurred during the mission, all results are based on computational estimates.

Four of the study's 22 authors are employed by StemRad, the company that makes the vest. The corresponding author, Dr. Milstein, is a co-founder and CEO of the company and holds two US patents related to the vest's design.

DOI: 10.1126/sciadv.adz1892

Jordan M. Houri et al., "First evaluation of wearable radiation protection for human deep space exploration, as flown on Artemis I." Sci. Adv. 12, eadz1892 (2026).