NIFTY: We’ve flown a radiation-blocking vest to the Moon and back, and it worked.

Spacecraft designers have spent decades weighing shielding options, from aluminum hulls to water-filled walls to superconducting magnets that would deflect charged particles before they reach the crew. All of them run into the same challenge. “The question was how to use mass in a very efficient way,” Milstein says. “Mass is really the bottleneck—every gram counts.”

A shielding garment an astronaut could wear is simultaneously sensible and ridiculous. The ridiculous part was that, for a long time, people thought that a protective garment would need to look like full-plate armor in order to offer meaningful protection. It would presumably need to be made of lead or other high-density materials that would add mass and make moving around nearly impossible.

StemRad engineers, though, figured dressing as a medieval knight doesn’t really get you all that much. The human body, Milstein explains, isn’t uniformly vulnerable to radiation. “Tissues like the bone marrow are a lot more sensitive to radiation compared to the brain,” he says. Following this idea, StemRad developed a belt for nuclear first responders, worn around the hips, which hold roughly half the body’s bone marrow, the tissue that makes blood cells. Protecting even a fraction of the bone marrow lets a person regrow it and survive a high-dose exposure.

So, StemRad, working with Lockheed Martin, expanded this idea into a female vest that, aside from the hips, also covered the breasts, stomach, colon, and reproductive organs. These are all less immediately life-threatening when irradiated, but carry a long-term cancer risk.

The details are intriguing.