NOAA's Space Weather Prediction Centre recorded Kp=7 overnight on 3 to 4 April, briefly reaching G3 Strong: the highest geomagnetic disturbance during a crewed deep-space transit since the Apollo programme 1. The storm escalated from the G2 conditions reported in Update 2 . A coronal mass ejection launched on 1 April, the same day as Artemis II, arrived as forecast. Conditions are now waning toward Kp=5.
Four astronauts coasted through this event beyond Earth's magnetosphere. Six HERA sensors and personal dosimeters aboard Orion are collecting readings. NASA's Space Radiation Analysis Group (SRAG) is in direct contact with NOAA forecasters 2. Flight controllers confirmed no operational impact. A preplanned radiation shelter protocol was available but not activated.
The number that matters most remains unpublished. Zero crew radiation dose data has been released through the entire G3 event. Only the top 5% of solar particle events produce nausea-level exposure, and the G3 storm does not appear to approach that threshold. The crew is fine. The spacecraft is fine. But the margin of safety rests on institutional trust, not verifiable data.
The two University of Michigan forecasting models deployed for live operational testing are receiving precisely the validation environment their research team sought. No performance assessment has been published.
