To Protect Artemis II Astronauts, NASA Experts Keep Eyes on Sun

As four astronauts travel around the Moon on NASA’s Artemis II mission, they will venture beyond Earth's protective magnetic field. The crew’s spacecraft, Orion, will carry and protect them as they journey into deep space and serves as the main protection against the Sun’s intense power.  During their 10-day flight, NASA and the National Oceanic and Atmospheric Administration (NOAA) will monitor the Sun around the clock and translate space weather conditions into real-time decisions to protect the astronauts. 

Space weather refers to the changing conditions driven by solar wind and eruptions from the Sun. Solar flares are the most powerful eruptions in the solar system, the strongest unleashing more energy than a billion hydrogen bombs. Coronal mass ejections are giant clouds of solar particles hundreds of times the size of Earth that burst from the Sun.  

While both flares and coronal mass ejections can affect technology, the primary concern for astronauts is the solar particle events they can trigger, accelerating some particles to near light speed. If a significant solar particle event occurs near the Artemis II crew, it could raise radiation levels inside the spacecraft. Too high a total lifetime exposure can contribute to increased risks of developing cancer or health disorders that could impair cognition and performance. During the Artemis II mission, NASA will minimize that risk.

For the first time in half a century, four astronauts are leaving Earth’s protective magnetic field to enter a realm where massive solar eruptions can unleash more energy than a billion hydrogen bombs. The Artemis II crew will fly through a dangerous environment, but they’re not going it alone. On the voyage, the astronauts and their Orion capsule are outfitted with radiation trackers as ground teams monitor solar eruptions 24/7. Here’s how NASA and the National Oceanic and Atmospheric Administration (NOAA) are protecting explorers from the most powerful eruptions in the solar system.
NASA/Joy Ng

Tracking solar eruptions 

“Our focus will be real-time space weather analysis, prioritizing solar energetic particles and events that could produce them,” said Mary Aronne, operations lead for the space weather analysis office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re looking for the trigger, which would typically be a flare or a coronal mass ejection.” 

This animation shows a solar eruption that produces a solar flare, a coronal mass ejection, and a flurry of energetic particles. The particles follow the spiral shape of the solar wind's magnetic fields into interplanetary space.

NASA's Goddard Space Flight Center Conceptual Image Lab

The Goddard team will track any solar eruptions that occur, measuring how big they are, how fast they’re moving, and how likely they are to generate energetic particles that will cross Orion’s path. To this end, they’ll use real-time data from Sun-watching spacecraft strategically placed across the solar system, such as NASA’s recently launched Interstellar Mapping and Acceleration Probe, NASA’s Solar Dynamics Observatory, the ESA (European Space Agency)/NASA Solar and Heliospheric Observatory, NOAA’s Geostationary Operational Environmental Satellites-19 satellite, and many others. 

Other NASA spacecraft also will help monitor the Sun. Due to Mars’ current position, NASA’s Perseverance Mars rover can look at the far side of the Sun, where Earth has no view. The rover’s Mastcam-Z cameras can give NASA’s space weather teams a view of the largest sunspots up to two weeks earlier so the team can monitor and prepare for possible solar flares.  

NASA’s Perseverance Rover captured these images of sunspots crossing the Sun from its vantage point on the Martian surface between February 24 - 27, 2026. Mars is currently on the opposite side of the Sun, giving the rover a view of sunspots not visible from Earth. Perseverance will monitor sunspots leading up to and during the Artemis II launch window, giving the Moon to Mars Space Weather Analysis Office (M2M SWAO) and Space Radiation Analysis Group (SRAG) teams advance notice of regions that could produce solar eruptions before they rotate onto the Earth-facing side of the Sun.

NASA/JPL-Caltech/ASU/MSSS/SSI

Monitoring crew exposure 

Energetic solar particles don't stream straight out from the Sun. They spiral along the Sun’s magnetic field lines, tracing loops tens of thousands of miles across and scattering due to particle collisions along the way. The chaotic swarm is so large that, from inside it, particles seem to be coming from every direction.  

“It’s more like you’re sitting in a bathtub and it’s gradually filling with water,” said Stuart George, a space radiation analyst at NASA Johnson. 

That gradual rise in radiation gives analysts time to evaluate the situation. Inside Orion, six radiation sensors, part of the Hybrid Electronic Radiation Assessor system designed and built by NASA, measure dose rates in different parts of the cabin. Artemis II astronauts also wear personal radiation trackers called crew active dosimeters. If radiation levels increase, Orion’s onboard systems display warnings accompanied by an audible alarm. 

Artist’s concept of the components of the Orion spacecraft.

NASA

NASA has dosage level thresholds they'll look for inside Orion. The first threshold signals a caution, prompting closer monitoring and coordination with medical and flight operations teams. A higher threshold triggers a recommendation for the crew to take shelter. 

Radiation shielding in space is all about mass. Charged particles are slowed and absorbed as they pass through matter. Astronauts are trained to reconfigure their cabin during a solar particle event, removing stowed equipment from storage bays and securing it along areas of the cabin to add mass between themselves and incoming particles. Since Artemis II is the first crewed Artemis mission, testing this procedure in the Orion spacecraft is a major objective of the mission. 

“Once crews add mass to the places that tend to be hotter in terms of radiation exposure, they can then continue to go about their duties,” George said. 

Artist’s concept of the Trajectory for Artemis II, NASA’s first flight with crew aboard SLS and Orion to pave the way for long-term return to the Moon and missions to Mars.

NASA

The complexity of solar particle events is one reason NASA places spacecraft across the solar system. During a solar storm in January, NASA analysts tracked a coronal mass ejection on its way to Earth. When it arrived, satellites detected two distinct spikes in energetic particles where there would normally be one. Measurements from NASA’s BioSentinel CubeSat, deployed during the Artemis I mission, revealed what happened. The spacecraft, about 55 million miles away from Earth, detected a distinct eruption that later merged with the coronal mass ejection headed to Earth. Ultimately, two separate eruptions occurred.

The crew also must account for exposure to Earth’s radiation belts and galactic cosmic rays. The Van Allen Radiation Belts are two rings of high energy particles that surround our planet. Any mission headed to the Moon or farther must pass through them. Galactic cosmic rays are very high-energy particles from sources beyond our solar system. Together, the radiation exposure from these sources is expected to be comparable to a 1-month stay on the International Space Station, or about 5% of an astronaut’s career limit. Any exposure from solar radiation events would add to this baseline. 

The Moon to Mars Space Weather Analysis Office, based at NASA Goddard, continuously assesses solar activity and any eruptions that occur. The team shares its analysis with the Space Radiation Analysis Group, based at NASA’s Johnson Space Center in Houston. Together, their forecasts and those from NOAA’s Space Weather Prediction Center, plus real-time measurements from inside the Orion spacecraft will inform recommendations for the flight control team.  

By Miles Hatfield
NASA’s Goddard Space Flight Center, Greenbelt, Md. 

Source: To Protect Artemis II Astronauts, NASA Experts Keep Eyes on Sun  - NASA Science