Enhanced Radiation Barriers and Artemis Radiation Levels Assessment

Enhanced Radiation Barriers and Artemis Radiation Levels Assessment

The Perilous Presence of Galactic Cosmic Rays in Deep Space Travel

Although solar flares pose a well-known danger to astronauts, another form of radiation, Galactic Cosmic Rays (GCRs), presents an often-overlooked hazard for those venturing beyond Earth's magnetosphere. These highly energetic particles, primarily protons and heavy ions, can have energies ranging from hundreds of MeV to tens of GeV or more.

During NASA's Artemis I mission, sophisticated instruments within the Orion spacecraft recorded radiation levels lower than expected given the estimated average GCR flux of approximately 3 particles per square centimeter per second at ~1 GeV. This discrepancy results from a combination of factors related to shielding, detector sensitivity, energy thresholds, and secondary radiation.

1. Spacecraft shielding and detector sensitivity: Orion's multi-layered aluminum and polyethylene hull provides substantial shielding, attenuating many lower-energy particles and reducing the overall flux. However, the most energetic GCR particles penetrate the spacecraft with minimal energy loss, passing quickly through detectors and depositing less energy per interaction, making them harder to detect or distinguish from background noise.
2. Detector energy thresholds and saturation: Some active detectors are calibrated to measure energy deposition within specific ranges, which can lead to complications when extremely high-energy particles traverse detectors with minimal interaction or cause overlapping signals during intense radiation events, making accurate flux measurement challenging.
3. Secondary radiation and dose contribution: High-energy GCRs interact with spacecraft materials to produce secondary particles, such as neutrons, protons, and lighter ions, that contribute significantly to the measured dose. Consequently, the dose equivalent recorded reflects a combination of primary GCRs and secondary radiation.
4. Measurement location and shielding variation: Sensors places in different locations within the spacecraft may detect lower fluxes due to variations in local shielding thickness and geometry. The Artemis I data show a variable radiation landscape inside the spacecraft, indicating an average flux that doesn't accurately represent the unshielded GCR flux in free space.

The challenges of shielding high-energy GCRs are significant. Given their range of many centimeters of aluminum-equivalent material, it is impossible to completely stop them without adding excessive mass. Increased shielding thickness can reduce lower-energy particles but may increase secondary radiation, which also contributes to dose. To strike a balance between mass constraints and dose reduction, Artemis I employed a shielding strategy that provided roughly 50% dose reduction during Van Allen belt crossings and effective protection during solar particle events.

The recorded radiation doses during Artemis I (26.7-35.4 mSv over ~25 days) are indicative of effective shielding and operational protocols that keep exposures below NASA career limits for lunar missions. However, high-energy GCRs still pose long-term risks, including vision impairment. To minimize these risks, Artemis employs countermeasures such as the AstroRad radiation vest to protect radiosensitive organs like eyes, and operational strategies like using storm shelters and limiting extravehicular activities during solar storms.

In conclusion, the discrepancy between the estimated average GCR flux and measurements aboard the Artemis I spacecraft arises because the highest-energy GCRs are difficult to fully detect and cannot be completely stopped by spacecraft shielding. Instead, a combination of Artemis's multi-layer shielding, advanced detectors, and operational protocols effectively reduces astronaut radiation exposure to safe levels for lunar missions while acknowledging the unavoidable penetration of high-energy cosmic rays.

As NASA prepares for longer-duration deep-space missions, improving shielding materials, active magnetic shielding concepts, and biological countermeasures will be essential in protecting crews from the full spectrum of space radiation.

Sources:- Space radiation measurements during the Artemis I lunar mission, Nature (2024)- Artemis I Radiation Measurements Validate Orion Safety for Astronauts, NASA (2023)- Comparison of Artemis I Radiation Measurements with Orion EFT-1 and ISS Data, Texas Tech University (2023)- Measurements of Materials Shielding Properties with 1 GeV/nuc 56Fe, Lawrence Berkeley National Laboratory (2010)

1. Space-and-astronomy: Despite advances in spacecraft technology, the challenge of shielding high-energy Galactic Cosmic Rays (GCRs) remains significant in deep space travel due to their extreme energy levels and inability to be completely stopped.
2. Health-and-wellness: As NASA prepares for longer-duration deep-space missions, taking care of astronauts' health and wellness requires continued research and implementation of improved shielding materials, active magnetic shielding concepts, and biological countermeasures to protect crews from the full spectrum of space radiation.

Read also: