The most important data from NASA’s first crewed Artemis II mission may not be its photographs, but the radiation measurements that will shape how humans work and survive beyond travel farther from Earth’s magnetic shelter safely.
Artemis II science operations will lay the foundation for safe and efficient human exploration of the Moon and Mars.
The investigations will encompass human health, lunar science, CubeSats, Science Operations and Space weather.
One of ANSTO's radiation dosimetry experts, Dr Mitra Safavi Naeini (pictured left) explored the approach undertaken by NASA.
When NASA launched Artemis II on 1 April 2026, sending Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen on a 10-day lunar flyby, it sent humans beyond low Earth orbit and back into the deep-space radiation environment for the first time since the Apollo program.
Radiation is one of the mission’s core scientific and operational questions. Along with four astronauts went cabin monitors, crew-worn dosimeters, an upgraded German heavy-ion detector, organ chits, saliva and blood sampling, and performance studies. The flight is testing the Orion and the Space Launch System with a crew aboard, but it is also characterising the radiation field inside the spacecraft, measuring how that environment field changes with trajectory and shielding, and linking those physical measurements to biomarkers, performance data and biological experiments.
The radiation environment
The first thing to get right is that 'radiation level' is not a single number. Beyond Earth orbit, astronauts face three overlapping hazards: trapped particles in the Van Allen belts, solar particle events from the Sun, and galactic cosmic rays from outside the solar system. The belts are intense but brief—the spacecraft crosses them quickly. Solar particle events are intermittent and operationally urgent; they can raise dose rates sharply over hours. Galactic cosmic rays are the chronic background: a low-dose-rate field of very high-energy particles, mostly protons but also heavy ions, present all the time and notoriously difficult to shield against.
Radiation science in space is hard because none of this reduces to a single number. Raw absorbed dose is only the beginning. A gray tells you how much energy is deposited, now how much biological trouble that energy will cause. There are more than fifty shades of gray (Gy) in space. Dose rate matters. Particle type matters. Direction matters. Shielding matters. Artemis II is flying in the unsettled aftermath of Solar Cycle 25’s maximum, which creates a useful paradox: the chronic galactic cosmic ray background is somewhat lower around solar maximum, but the chance of a disruptive solar storm is higher.
A proton storm and a background field of heavy ions are therefore biologically different problems, even if a headline number makes them look comparable. Radiation teams therefore care about quantities related to radiation quality, including quantities such as linear energy transfer, because densely ionising particles do more biological damage than the same absorbed dose delivered by sparsely ionising radiation.
Shielding adds another layer of complexity. For solar proton events, extra material helps a considerably. For galactic cosmic rays, the benefit becomes more counterintuitive: it is much smaller when very energetic ions hit spacecraft wall—or body itself—they can fragment and generate secondary radiation, including neutrons—and interactions in shielding generate secondary particles that complicate the picture further.
Artemis I already demonstrated why that nuance matters. The uncrewed mission found that Orion’s shielding was effective for a lunar flight, but exposure varied by location within the cabin and by spacecraft orientation. During one passage through the radiation belts, a change in orientation during an engine burn reduced measured radiation levels by nearly half.
Radiation protection in deep space is therefore partly a materials problem, but it is also a geometry and operations problem—and Artemis II is the first mission to map this geometry with crew on board. Orion carries six Hybrid Electronic Radiation Assessors, active crew dosimeters worn by the astronauts, and updated M-42 EXT detectors from the German Aerospace Centre with much finer energy resolution than Artemis I version. Together they provide time-resolved measurements of the environment where the crew actually live and work.
If the Sun produces a significant solar particle event during the mission, they help Mission Control decide when the crew should shelter and where inside Orion is safest. In practice, that can mean decisions about turning response: whether to change activity, how to use available stowage and water as a makeshift storm shelter inside the vehicle, additional shielding, and where the best-protected volume inside Orion really is.
For living systems, Artemis II goes beyond counting particles. The AVATAR experiment is flying bone-marrow-derived organ chips (see image above) made from each the astronaut’s’ own cells inside a self-contained payload. Bone marrow is a logical target because it is central to immune function and particularly sensitive to radiation.
NASA is also collecting immune biomarkers through saliva and blood sampling, while ARCHeR and Standard Measures track sleep, stress, cognition, performance and other physiological responses. One of most interesting questions is whether the same physical dose field translates into the same biological injury in different people. Radiation never acts in isolation. On a real mission it is layered with microgravity, confinement, altered sleep, workload, heat, carbon dioxide, and distance from Earth.
In Part 2: Learn what one moon flyby can and cannot do and what is next