Almost two years after the Artemis 1 mission, which tested the unmanned Orion spacecraft in a flight around the moon, the first scientific paper on radiation levels measured en route to the moon was published last week.
The Israeli-American company StemRad, which develops a protective vest designed to shield astronauts from particle radiation during intense solar storms, participated in the experiment. The experiment was conducted with the participation of the Israel Space Agency and was led by researchers from the German Space Agency (DLR) and NASA.
Effective shielding
During the experiment, radiation levels were measured by numerous sensors placed throughout different parts of the spacecraft, as well as on and inside two human-sized mannequins, Helga and Zohar. One was fully exposed, while the other was equipped with the Israeli protective vest. The article published in Nature does not yet discuss the performance of the Israeli vest, focusing instead on a general overview of the radiation levels recorded during the mission.
These levels were encouragingly low in terms of the risk level for astronauts on such missions. "This is the first time we've continuously measured radiation levels in a spacecraft designed to carry humans beyond Earth's magnetic field. The Orion spacecraft’s design includes radiation shielding, and we can attribute the relatively low measurements to this shielding compared to what was recorded during the Apollo program," explained Dr. Christine Hellweg, head of the department of Radiation Biology at the Institute of Aerospace Medicine at the DLR, in an interview with the Davidson Institute website.
The radiation that the shielding is intended to block consists of charged particles (ions),primarily emitted by the sun, traveling through space at extremely high speeds, nearing the speed of light. Earth is relatively protected from this radiation by its magnetic field, which traps these particles in two layers known as the Van Allen belts, named after the researcher who discovered them. As the spacecraft passes through these belts—especially the denser inner belt—it is exposed to higher levels of radiation.
At this stage, the most shielded area of the spacecraft, referred to as the “shelter,” plays a crucial role. "In the less shielded areas, radiation levels during the inner belt crossing were four times higher than in the most shielded area," Hellweg explained. "The continuous measurement of radiation levels throughout the mission allows us to plan the mission's duration and characteristics according to the amount of radiation astronauts are expected to encounter at each stage: passing through the belts, deep space travel, orbiting the moon, and landing on its surface. It also helps us design optimal shielding for each stage.”
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Inside the spacecraft: the mannequins Helga (right) and Zohar, with the protective vest, aboard the Orion spacecraft
(Photo: NASA/Lockheed Martin/DLR )
Beyond the Van Allen belts, the main radiation the spacecraft was exposed to came from galactic cosmic rays—particles originating from outside our solar system—which have a much lower intensity. Another significant risk factor is the potential increase in radiation levels during solar storms. These events involve a significant increase in particle radiation emitted by the sun, known as the "solar wind." Despite the general activity cycles of the sun, solar storms cannot be predicted in advance to plan space missions accordingly. During the 25 days of the Artemis 1 mission, no significant solar eruptions occurred. Nonetheless, Hellweg noted that the findings indicate the spacecraft would remain safe even during such events.
“In terms of radiation exposure, the Orion spacecraft is safe for a lunar journey in accordance with the framework of the Artemis program, for a duration similar to Artemis 1 during 'quiet' periods of the sun,” she clarified. “In the event of a strong solar storm, astronauts would need to remain in the more shielded part of the spacecraft. The mission data, combined with simulations we've conducted, show that even during a strong solar storm, the shelter provides good protection, and astronauts are unlikely to suffer from radiation sickness (the symptoms caused by rapid exposure to a high dose of radiation).”
En route to mars
The findings on radiation levels from the Artemis 1 mission were so encouraging that the authors of the article even used them to estimate the expected radiation exposure levels for a mission to Mars aboard the Orion spacecraft or a similarly shielded vehicle. This is despite the fact that such a mission would be much longer—the round trip to and from Mars is expected to take about a year and a half. “Projections for a manned mission to Mars indicate radiation levels 30% lower than previously calculated, meaning that in such a mission, including a short stay on Mars, astronauts would not exceed NASA’s maximum allowable cumulative radiation exposure level, provided solar activity remains similar to that during the Artemis 1 mission,” Hellweg explained.
As mentioned, this article did not examine the Israeli part of the experiment— the effectiveness of the "AstroRad" protective vest and the level of protection it provides against radiation. This data is expected to be published in the coming months in a follow-up article. As we previously reported, an initial analysis of the findings showed that the vest effectively protected the Zohar mannequin. “The AstroRad vest shields internal organs sensitive to radiation during periods of heightened solar activity,” Hellweg noted. “During weak or moderate solar storms, it will allow astronauts to continue their regular activities aboard the Orion spacecraft. In the event of strong or extreme storms, when astronauts need to take refuge in the spacecraft’s shielded area, it will provide an additional layer of protection, reducing the radiation dose absorbed, ensuring it does not exceed dangerous levels, and minimizing the long-term risks of radiation exposure, such as cancer.”
“The data on the vest that protected Zohar during this journey will be published soon and will highlight its importance, both in terms of health and operational efficiency,” said StemRad co-founder and CEO Dr. Oren Milstein to the Davidson Institute website. “The article now published in Nature demonstrates the capabilities of the Orion spacecraft to take us further— to the Moon and even to Mars. Radiation protection will become increasingly important as we advance on this exciting journey for humanity.”
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