In late 2022, NASA's Orion spacecraft carried two dummies - Helga and Zohar - as part of the MARE project, led by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR), along with numerous radiation sensors. The dummies embarked on a 25-day round-trip journey to the Moon and back, providing continuous data on radiation levels between Earth and the Moon, a distance of almost 500,000 kilometers. The initial findings, now published in Nature, offer valuable insights into space radiation exposure.

Thomas Berger, a radiation physicist at the DLR Institute of Aerospace Medicine in Cologne and the Principal Investigator for the MARE experiment, explained: "We had two main objectives for the Artemis I mission. For the first time, we wanted to collect a comprehensive and coherent data set on the radiation conditions during a lunar flight, and we are still analysing this data. And, together with NASA and ESA, we wanted to characterise the variations in radiation exposure inside the Orion spacecraft, for which the results are now available."

Berger went on to explain that numerous dosimeters (radiation detectors) were strategically placed in different locations throughout the spacecraft and inside the life-size mannequins Helga and Zohar. The MARE project is a collaboration between DLR, the Israeli company StemRad, NASA, Lockheed Martin, and the Israeli Space Agency (ISA).

Key findings: Radiation levels varied significantly inside Orion

The data, now available in Nature, shows significant differences in radiation exposure inside the spacecraft as it passed through Earth's proton belt (the inner Van Allen belt). Depending on the position of the detectors, radiation exposure varied by a factor of four. This variation validates the design and shielding of the Orion spacecraft. In the most shielded part of the spacecraft (the Storm Shelter), radiation levels during intense solar events were capped at 150 millisieverts, which is below the threshold for acute radiation sickness.

Suitability of Orion for human missions
The data also indicates that spacecraft orientation during the proton belt passage significantly influenced the radiation exposure. A 90-degree turn at the end of the inner Van Allen belt passage reduced radiation exposure by 50 percent. "This shows us that this flight manoeuvre can significantly reduce the radiation exposure for the crew. This is also a good sign and confirms the basic suitability of Orion for future spaceflight with astronauts. Our measurement data also provides a solid knowledge base for the design of future missions," Berger emphasized.

The study also highlights that modern computer simulations of radiation environments are increasingly accurate. Experimental measurements largely aligned with predicted models, supporting future cost-effective development of radiation protection technologies for Orion and other spacecraft.

The findings suggest that radiation exposure during future Artemis missions, lasting a few days to several weeks, will remain within NASA's current safety limits for astronauts, provided mission conditions remain similar. However, managing radiation exposure remains a critical challenge for long-term human spaceflight.

Joint efforts by NASA, ESA, and DLR to protect Orion's future crews
The Artemis I mission marked the beginning of NASA's broader Artemis program, which aims to return humans to the Moon, establish a permanent lunar base, and create a space station in lunar orbit as a stepping stone to Mars. The first uncrewed Artemis I mission launched on November 16, 2022, from Kennedy Space Center, combining new systems: the Orion spacecraft, the European Service Module (ESM), the Space Launch System (SLS) heavy-lift rocket, and ground systems.

NASA equipped Orion with the Hybrid Electronic Radiation Assessor (HERA) to monitor radiation levels. This system includes three sensors placed in different shielded areas of the spacecraft to trigger alerts in the event of high-energy radiation events, such as solar flares. If such an event occurs, astronauts will be directed to seek shelter in more shielded areas, installing additional material over their heads for added protection.

ESA contributed five mobile dosimeters (EAD-MUs) to monitor radiation across the spacecraft. These systems have been used previously on the International Space Station (ISS), and data from Artemis I will help refine safety measures for future crewed Artemis missions. A future version of this system will be deployed on the planned Lunar Gateway station orbiting the Moon.

The DLR Institute of Aerospace Medicine developed both the ESA dosimeters and DLR's own M-42 radiation devices, used in conjunction with passive sensors inside Helga and Zohar. "The detectors measure different types of radiation, enabling us to use the values to draw conclusions about their biological effects," Berger noted. Both mannequins were designed to mimic female anatomy, allowing researchers to study how radiation affects women during long-duration space missions.

The Nature publication represents only the first set of results. Ongoing analysis of the radiation data from Artemis I will continue. Currently, the DLR MARE team is comparing data from Helga, who flew unprotected, and Zohar, who wore the AstroRad vest, to assess the effectiveness of radiation shielding.

Research Report:Space radiation data gathered during Artemis I lunar mission

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MARE project
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