A radiation shielding vest flown on the uncrewed Artemis I mission in 2022 cut effective dose by around 60% in simulations of an August 1972-type solar particle event, and by almost 40% in an October 1989-type event, according to results published in Science Advances.

The AstroRad vest, developed by StemRad Radiation Protection with Lockheed Martin since 2015, spares astronauts the dose equivalent of up to 193 and 131 days of deep-space travel in those two scenarios respectively.

"Exposure to radiation in space is unavoidable, and a single major solar particle event (SPE) can deliver more than one-third of NASA's 600 millisievert career effective-dose limit," said Oren Milstein, an immunologist and CEO of StemRad. "A three-year round trip to Mars would equal or exceed the career limit, which corresponds to a 3% mortality risk from radiation-induced cancer. So we developed the AstroRad vest to significantly reduce this hazard."

How was the vest tested?

The analysis rests on data from two human-tissue-equivalent female torso phantoms seated in the Orion crew capsule during Artemis I. The "Zohar" phantom wore the AstroRad vest; its companion "Helga" did not. Dosimeters placed in and on both phantoms allowed direct comparison of received dose.

Artemis I encountered no solar storm, but Orion traversed the inner Van Allen belt, whose protons span a similar energy range to SPE protons. The team used this to build a Monte Carlo model of the experiment.

"We created digital twins of Helga and Zohar, the AstroRad vest, radiation detectors and spacecraft shielding," said Jordan Houri, lead scientist for space exploration at StemRad. "Using this model, we generated hundreds of billions of virtual protons and electrons representing the radiation environment of the inner Van Allen belt, before comparing the predicted detector responses directly with the measurements recorded during Artemis I."

The predicted and measured detector responses agreed closely, which the researchers say validates the model. They then used it to simulate the two historical SPEs. These are projections grounded in measured flight data, not dose reductions recorded during an actual storm.

Why target organs selectively?

Shielding thickness varies across the garment according to the radiation sensitivity of underlying organs. Breasts, colon, lungs, ovaries, stomach and red bone marrow received concentrated shielding in the test vest.

Milstein traces the design logic to his PhD supervisor, who treated first responders at the 1986 Chernobyl disaster. Bone marrow damage was the accepted cause of death for those emergency workers who died within months of the accident. "That heritage instilled in me a desire to protect people from radiation by selective shielding of the bone marrow," Milstein said.

The experiment focused on female phantoms because women carry a higher predicted risk of radiation-induced cancer than men.

For flexibility, the vest uses thousands of hexagonal tessellated rods of high-density polyethylene (HDPE) sandwiched between elastic fabric layers. The rods slide past one another and stretch. HDPE was selected for its high hydrogen content, effective against charged-particle space radiation.

What does it change for mission planning?

Astronauts currently ride out SPEs in "storm shelters" built from barricades of supplies, or by moving to cabin areas with more wall hardware. AstroRad matches the protection of the most robust shelter configuration while "allowing the astronaut wearing it to move around the cabin and continue mission-critical tasks," Houri told Physics World.

The team is combining these dosimetry results with earlier ergonomics experiments on the International Space Station to improve comfort, ease of motion and mass. One option under study: launching lighter, empty vests and filling them with recycled polyethylene after launch.

Beyond crew health, Milstein argues the economics favour shielding, since reduced exposure extends astronaut careers. He hopes AstroRad can "make lunar habitation and Mars travel truly sustainable and not just a dream."

The researchers plan to keep iterating the design as additional ergonomics and mass-reduction data come in.