Space radiation is a significant hazard for long-duration human space exploration, potentially impacting astronauts’ health through increased cancer risks, degenerative diseases, and other tissue damage. For the uncrewed Artemis I lunar mission, radiation exposure was a key focus, as this mission marked a step toward enabling future human spaceflights beyond low-Earth orbit. Measurements were taken aboard the heavily shielded Orion spacecraft, contributing valuable data about radiation exposure in interplanetary space and inside the Earth’s Van Allen belts. The detailed findings are outlined in the study titled “Space radiation measurements during the Artemis I lunar mission”, which provides essential insights into radiation shielding and space travel.
This article outlines the key findings from radiation measurements taken during the Artemis I mission. The findings have implications for spacecraft shielding design and mission planning, especially as human spaceflight ventures deeper into the solar system.
Space Radiation Hazards
Space radiation originates from multiple sources, including galactic cosmic rays (GCRs), trapped-particle radiation (such as the Van Allen radiation belts), and solar-particle events. Each of these sources poses unique challenges:
- Galactic Cosmic Rays (GCRs): High-energy particles from outside the solar system. These are a constant source of radiation in interplanetary space and are difficult to shield against.
- Trapped-particle radiation: These are primarily electrons and protons trapped in Earth’s magnetic field, forming the Van Allen belts. When spacecraft pass through these belts, radiation exposure can significantly increase.
- Solar Particle Events (SPEs): Intense bursts of radiation from solar flares or coronal mass ejections that can drastically increase radiation exposure for astronauts.
The effects of space radiation on human tissue include increased risks of cancer, cataracts, cardiovascular disease, and acute radiation sickness. Understanding these risks is essential for mitigating exposure during long-duration missions to the Moon, Mars, or beyond.
The Orion Spacecraft and the Artemis I Mission
The Orion spacecraft, designed to carry humans to deep space, was equipped with advanced radiation measurement instruments for the uncrewed Artemis I mission. Key to this mission was validating the spacecraft’s radiation shielding and understanding the radiation environment astronauts would experience during future missions.
The NASA HERA (Hybrid Electronic Radiation Assessor), European Space Agency Active Dosimeter (EAD), German Aerospace Center M-42 detector, and the NASA Crew Active Dosimeter (CAD) were among the instruments used to measure radiation inside Orion. Measurements were taken in various parts of the spacecraft, each with different levels of shielding.
Two radiation phantoms, Helga and Zohar, life-size female mannequins equipped with radiation sensors, were used to simulate how radiation would affect human tissue. These phantoms allowed for precise measurement of radiation doses at different body locations, providing critical data on how radiation penetrates the human body.
Inner Proton Belt Measurements
The Artemis I mission provided key insights into radiation levels while passing through the inner proton belt, which consists primarily of high-energy protons trapped in Earth’s magnetic field. As the spacecraft passed through this region, a fourfold difference in radiation dose rates was observed, depending on the location and shielding within the spacecraft.
For instance, measurements showed the following dose rates at different shielded locations:
- M-42 SN127: 69 µGy/min at the most shielded location.
- EAD MU01: 240 µGy/min at the least shielded location.
- HERA HSU2: 287 µGy/min.
These results demonstrated that Orion’s design effectively reduced radiation exposure during proton belt passes, validating the spacecraft’s shielding design against solar-particle events.
Galactic Cosmic Rays in Interplanetary Space
Once the spacecraft exited the Earth’s radiation belts, it spent 25 days in the interplanetary galactic cosmic ray (GCR) environment. Unlike the proton belt, where shielding had a significant impact, the effects of shielding on GCRs were much smaller. GCRs are high-energy, highly penetrating particles, and reducing their biological effects requires substantial shielding.
During the Artemis I mission, dose rates from GCRs were similar across all the measuring instruments, indicating that the spacecraft’s shielding was less effective in reducing GCR exposure. However, an unexpected reduction of about 30% in GCR exposure occurred when the spacecraft was positioned behind the Moon, which acted as a natural shield against GCRs.
Spacecraft Orientation and Radiation Exposure
During the mission, the Orion spacecraft’s orientation had a notable effect on radiation exposure. As the spacecraft rotated during a trans-lunar injection maneuver, a 50% reduction in radiation dose rates was observed. This decrease was attributed to the spacecraft’s bulkier parts, including the airlock and second-stage equipment, blocking incoming radiation from the inner proton belt.
This finding suggests that spacecraft orientation can be a useful strategy in minimizing radiation exposure, particularly during high-risk solar-particle events or belt passes.
Simulations and Validation of Shielding Models
The Artemis I mission also provided an opportunity to validate radiation shielding models. Using tools such as HZETRN and Geant4, which simulate how radiation interacts with shielding materials, researchers compared real-world measurements with predicted radiation levels.
The comparisons showed broad agreement between the simulations and the actual data collected during the mission. This validation is important for future mission planning, as accurate models can help design spacecraft with optimal shielding, reducing risks for astronauts.
Dose Equivalents and Health Implications
The total radiation dose equivalent during the Artemis I mission ranged from 26.7 to 35.4 mSv, depending on the location within the spacecraft. While GCRs contributed the majority of the dose, the proton belt crossing also added significant exposure.
To put these values into perspective, NASA sets a career limit of 600 mSv for astronauts, designed to limit their cancer risk to 3% above the baseline for a 35-year-old female astronaut. The radiation levels observed on Artemis I were well below this limit, and future Artemis missions of similar duration are not expected to exceed it.
For future missions to Mars, radiation exposure is expected to be higher, but the data from Artemis I suggest that even on a mission to Mars, radiation doses could potentially be managed within acceptable limits, depending on shielding and mission duration.
Implications for Future Human Spaceflight
The radiation measurements during Artemis I provided essential data that will inform the design of future spacecraft and space missions. Key takeaways include:
- Spacecraft Shielding: Orion’s shielding was validated during both proton belt passes and GCR exposure in deep space, showing effective radiation protection in different environments.
- Spacecraft Orientation: The orientation of the spacecraft plays a crucial role in minimizing radiation exposure. Aligning the thickest parts of the spacecraft with incoming radiation can significantly reduce dose rates.
- Radiation Models: The validation of radiation shielding models with real-world data is critical for planning future missions, especially those involving long-term exposure to GCRs and solar-particle events.
- Human Health: The radiation exposure levels measured during Artemis I provide confidence that radiation risks can be managed for future human lunar and Mars missions, particularly with continued improvements in shielding design.
As NASA continues to plan for crewed missions beyond low-Earth orbit, the findings from Artemis I will be integral in shaping strategies to protect astronauts from space radiation, ensuring that humanity’s expansion into deep space is done as safely as possible.
