Four astronauts are preparing to fly around the Moon on a roughly 10-day mission, and for the entire trip, teams on the ground will be watching the Sun as closely as they watch the spacecraft. NASA and NOAA plan to provide continuous space-weather monitoring and decision support during Artemis II, NASA’s first crewed Artemis mission around the Moon, because solar activity can raise radiation levels that pose a key risk to crews traveling beyond Earth’s protective magnetic field.
Why Solar Storms Threaten Lunar Crews
Astronauts aboard the International Space Station work inside Earth’s magnetic field, which deflects most charged particles hurled outward by the Sun. The Artemis II crew will not have that shield. As four astronauts venture beyond Earth’s protective magnetic field, they become directly exposed to solar particle events, the primary radiation risk identified by NASA for this mission. These events occur when solar flares or coronal mass ejections accelerate protons and heavier ions to dangerous speeds, flooding interplanetary space with radiation that can penetrate spacecraft walls and human tissue.
The danger is not limited to biology. Severe or extreme solar activity increases solar energetic particle density with the potential to damage electronic circuits and disrupt radio communications, according to NASA’s published weather criteria for the mission. That means a single intense eruption could simultaneously threaten crew health, spacecraft electronics, and the communication link back to mission control. For a crew orbiting the Moon with no quick way home, losing any one of those three is a serious problem.
A Joint Forecasting Operation
To counter that risk, NASA and NOAA have built a joint space weather operation that goes well beyond standard solar forecasting. NOAA’s Space Weather Prediction Center will provide specialized interpretive support for the full duration of the mission, working directly with NASA’s Space Radiation Analysis Group, known as SRAG. The arrangement means SWPC forecasters will not simply issue public bulletins. They will deliver tailored analysis to mission leadership and console operators in real time, focusing specifically on developments that increase the chance of radiation exposure to the crew.
The Goddard Space Flight Center team will track any solar eruptions that occur, measuring their size, speed, and likelihood of impacting the Earth-Moon system. NASA is also tapping an unusual asset: as NASA notes, because of Mars’ current position, the Perseverance rover can help monitor solar activity from a different vantage point, including regions of the Sun that are not directly visible from Earth at the same time. That extra vantage point could provide earlier warning of active regions rotating toward the crew’s line of exposure, a capability that did not exist during the Apollo program.
Launch Rules and the S1-to-S5 Scale
NASA has set an explicit launch constraint: the agency will not send Artemis II off the pad during severe or extreme solar activity. NOAA’s SWPC categorizes solar radiation storms on a scale from S1 (minor) to S5 (extreme), based on GOES satellite energetic proton flux measurements. Events at the higher end of that scale pose direct risks to humans in space and satellites alike. SWPC issues forecast and warning products for any event reaching S1 or above, and for Artemis II those warnings will feed directly into launch and mission decisions.
Mission planners will weigh several factors, including the current solar cycle phase, recent flare history, and the likelihood that an active region could produce additional eruptions. The formal weather criteria outline how proton flux thresholds, geomagnetic conditions, and ongoing radiation storms translate into launch commit rules. If conditions exceed those limits, the countdown will be halted, even if local weather at the launch site is perfect.
Most coverage of Artemis II treats the launch weather constraint as a simple go/no-go checkbox. That framing misses the harder question: what happens if a major eruption occurs after liftoff, when the crew is already en route to the Moon? The answer lies in a layered defense that combines external forecasting with onboard detection and well-rehearsed procedures.
Radiation Sensors Inside Orion
Inside the Orion capsule, six radiation sensors form part of the Hybrid Electronic Radiation Assessor, a system designed to monitor radiation at different shielding locations throughout the spacecraft. These devices can alert the crew to seek shelter during a solar storm. Each astronaut will also carry personal dosimeters in their pockets, measuring individual radiation exposure in real time. The gradual rise in radiation that typically precedes a full-blown solar particle event gives analysts on the ground time to evaluate the situation and relay guidance before conditions peak.
This onboard system represents a meaningful upgrade over what was available during Artemis I, the uncrewed test flight. That mission carried thousands of passive sensors and dozens of active detectors to map the radiation environment inside the capsule. The detailed findings, published by NASA in its Artemis I radiation measurements update, showed that Orion’s orientation and shielding helped reduce radiation exposure inside the capsule. For Artemis II, the crew will benefit from those validated shielding designs while also having real-time alerts that the uncrewed mission could only simulate.
NASA has also built radiation research directly into the Artemis II science portfolio. The mission will carry biomedical experiments and dosimetry investigations described in the agency’s overview of planned science, allowing researchers to correlate instrument readings, spacecraft configuration, and crew activities with measured exposure. Those data will inform designs for longer journeys to lunar orbiting stations and, eventually, Mars.
Rehearsing for a Solar Emergency
None of this coordination works without practice. In the April to May 2025 timeframe, NOAA SWPC, NASA SRAG, and NASA’s Moon-to-Mars Space Weather Analysis Office ran a multi-week spaceflight support exercise to rehearse their roles. Using simulated solar eruptions and radiation storms, forecasters practiced issuing alerts, while flight controllers walked through the steps they would take to protect the crew. The goal was to test not just the models and tools, but the communication pathways and decision timelines that would matter during a real emergency.
During such a scenario, the sequence would unfold quickly. Space weather models would flag a dangerous eruption and estimate when high-energy particles might reach the Earth-Moon corridor. SWPC would brief SRAG and mission control, highlighting expected intensity and duration. Onboard Orion, the Hybrid Electronic Radiation Assessor would confirm rising levels, while ground teams compared those readings to model forecasts. Within minutes, flight controllers could instruct the crew to take protective actions such as moving to the most shielded part of the capsule and postponing nonessential activities, consistent with procedures rehearsed in training exercises.
These rehearsals also force teams to confront edge cases. For example, what if a storm arrives while Orion is performing a critical engine burn, when the crew cannot immediately move to shelter? How should controllers weigh the risk of delaying that maneuver against the risk of added radiation exposure? By working through such trade-offs in a simulated environment, NASA and NOAA aim to refine playbooks before astronauts face those choices in deep space.
Building a Template for Future Missions
Artemis II is a relatively short mission, but the systems being tested are designed with a longer horizon in mind. The same solar monitoring network, forecasting models, and onboard sensors will underpin later Artemis flights that plan to send crews to a lunar orbiting platform and, eventually, to the surface. NASA’s broader Moon-to-Mars strategy assumes that astronauts will spend weeks to months outside Earth’s magnetic field, where cumulative radiation dose and rare, intense storms both matter.
For those future expeditions, the Artemis II approach offers an early template: combine global solar surveillance, rapid information sharing, strict launch rules, and real-time in-cabin monitoring. The mission’s radiation measurements, together with the outcomes of the joint exercises, will help determine how thick spacecraft walls must be, how much dedicated storm shelter volume is required, and how conservative launch rules should remain as crews push farther from home.
In that sense, the Sun is shaping human exploration plans as much as rockets and landers are. By treating space weather as a central mission design driver rather than a background concern, NASA and NOAA are trying to ensure that when Artemis II leaves the safety of Earth’s magnetic cocoon, the crew will have more than luck standing between them and the next solar storm.
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*This article was researched with the help of AI, with human editors creating the final content.
