NASA’s Artemis I mission brought back some very practical — and promising — information about protecting astronauts from radiation.
NASA engineer Stuart George and his colleagues recently delved into the data from dozens of sensors on the Orion capsule to learn more about what the Artemis I flight told us about Orion, astronauts, and space radiation, and overall the news is good for future Moon explorers. George and his colleagues published their work in the journal Nature.
The Adventures of Helga and Zohar
NASA’s Artemis I mission carried a crew of mannequins (well, one whole mannequin and two torsos, technically called “phantoms,” because that’s much less morbid) on its 2022 lap around the Moon. The pair of plastic and resin torsos, nicknamed Helga and Zohar, were each fitted out with more than 5600 instruments, including 34 radiation sensors in different parts of their bodies. Those sensors measured the dosage of radiation that Helga and Zohar received at different points during the flight — in a remarkable amount of detail. (Fun fact: astronaut’s right lungs absorb about 20% less radiation than their left lungs during a flight to the Moon.)
When Artemis II launches late next year, its Orion capsule will become the first crewed spacecraft in 53 years to venture beyond the protection of Earth’s magnetic field, which blocks most of the cosmic rays from deep space and electrically-charged particles from the Sun which would otherwise bombard our planet’s surface. Spacecraft in low Earth orbit, like the International Space Station, are partially shielded by the magnetic field, too. But beyond Earth’s magnetosphere, spacecraft have no protection from cosmic rays and solar wind, or the occasional full-on solar storm.
Crews flying to the Moon on the upcoming Artemis missions will rely on the Orion capsule’s radiation shielding, which is made with a combination of high-tech composite materials and aluminum. When the space weather gets really rough, astronauts will even have a storm shelter — a compartment in the middle of the ship, which usually serves as a storage space but can be emptied in a hurry so crews can take shelter. It’s the spacefaring equivalent of ducking into a storage closet when the tornado sirens go off.
The good news, based on data from Helga, Zohar, and instruments scattered around Orion, is that the storage closet actually makes a pretty good storm shelter for astronauts. And a few well-planned maneuvers can also help reduce the amount of radiation exposure Artemis crews might face at crucial moments, like flying through the Van Allen belts or riding out a solar storm. Orion is likely to be able to keep crews safe on even longer flights, like a future expedition to Mars.
Instruments on a wall inside the storm shelter and one out in the main crew cabin measured radiation doses as Orion passed through the lower Van Allen radiation belt (the same one the private mission Polaris Dawn just visited). It turns out that the sensor in the storm shelter recorded about half as much radiation as the one in the main crew cabin. Since that’s exactly what the storm shelter was supposed to accomplish, that’s good news for NASA and future Artemis crews.
No solar storm happened during the Artemis I flight, so the sensors only recorded how well the shelter worked while the spacecraft flew through the Van Allen belts. But George and his colleagues combined that data with a computer model of a 1989 solar storm to simulate what might happen – and it turns out the shelter should be even more effective against the radiation of a solar storm than the higher-energy radiation of the Van Allen Belts.
Evasive Maneuvers
In addition to ducking into the storage closet, astronauts may have an option to give themselves a little extra protection from incoming radiation: point the ship like a weather vane.
As part of the maneuver that set Artemis on a course from Earth orbit to the Moon, Artemis I rotated, pointing its nose into the flow of charged particles trapped in the Van Allen belt. And for those few minutes, the amount of radiation hitting the sensors in the ship’s cabin dropped by 50%. (Think about what happens when you’re driving through the rain and briefly drive through an underpass and you can get the picture.) The rotation put the bulkiest parts of the Orion capsule — the second-stage rocket at the back end, and the airlock up front — in between the cabin and the flow of radiation through the Van Allen belts.
And it made a tremendous difference.
That could be a useful trick for future missions, anytime astronauts are facing a flow of radiation or charged particles that mostly come from one direction in space – like passing through the radiation belts or riding out a solar storm. Since one of the mission abort options involves looping through Earth’s radiation belts several times, pointing the ship like a weather vane could be a handy part of the contingency plan.
What’s Next?
While NASA restricts its astronauts to a lifetime radiation dosage of 600 milliSieverts, the Artemis mannequins picked up just 26.7 (Zohar, who wore a radiation protection vest) and 35.4 (Zohar, with no vest) milliSieverts on their Moon mission. And that’s even without either mannequin having a seat in the storm shelter. Since future missions are about the same duration, George and his colleagues say, future astronauts should be able to safely make several round trips before worrying about how much radiation they’ve accumulated along the way.
A little math also shows that Orion may even be able to carry future astronauts to Mars without exceeding NASA’s safety limits, which are designed to minimize the long-term cancer risk from radiation exposure. George and his colleagues calculated how much radiation astronauts could expect to absorb on a flight to Mars in Orion, based on the Artemis I data. Their result suggests about 30% less radiation exposure than previous studies, which didn’t have the Artemis I data to work with.
“However,” George and his colleagues write in their recent paper, “the details of future missions will depend heavily on shielding, trajectory, modulation of galactic cosmic rays with the solar cycle, and severity of solar particle events.”
