Artemis 2 is days from launch, and NASA says it's a go. The solar storm risk that would have been a roll of the dice in 1972 now has a name, a sensor array, and a procedure.
NASA has deemed the mission GO. A solar flare occurred during the countdown window; it did not change the call. The radiation environment the crew will fly through is monitored in real time by six Hybrid Electronic Radiation Assessor sensors distributed throughout the Orion crew module, and the vehicle has a procedure for sheltering if a solar particle event occurs. The crew is trained to reconfigure the cabin — repositioning stowed equipment and supplies to add mass shielding between themselves and incoming particles — creating a protected zone that NASA Science describes in detail. Dosage thresholds aboard Orion trigger increasing response levels: a caution level prompts closer monitoring and coordination with medical and flight operations teams; a higher threshold triggers a recommendation for the crew to take shelter. NOAA's Space Weather Prediction Center provides the primary space weather forecasts that inform NASA's Space Radiation Analysis Group, which makes the GO or NO-GO call for the crew. The prediction window for a significant solar particle event is typically 24 to 48 hours.
That infrastructure — the sensor array, the shelter procedure, the forecast chain — did not exist during Apollo. The six HERA sensors measure dose rates continuously throughout the mission and feed data to the crew and mission control in real time. If levels rise, Orion's systems display warnings with an audible alarm. NASA's Artemis I radiation measurements confirmed the spacecraft can protect crew from hazardous radiation levels during lunar missions. Apollo had no equivalent. Sixty years of post-Apollo research into what solar particle events do to human physiology and spacecraft electronics built the system flying now.
The solar cycle is in its active phase. NASA and NOAA announced in October 2024 that the Sun has reached solar maximum, with the active period expected to continue for roughly a year — meaning the declining phase, during which significant solar storms remain possible, extends through 2025 and into 2026. NOAA's Space Weather Prediction Center predicts the cycle peak at a smoothed sunspot number of 115, with an error band spanning November 2024 through March 2026. Artemis 2 is flying through the tail of that window.
The astronauts on Artemis 2 are not flying blind. Orion carries radiation instruments that did not exist on the last crewed lunar mission. The SEP sensor was added because the next program needed it. That is worth noting as the first crewed lunar flight since 1972 approaches.
