Measurements of deep space radiation aboard the ispace RESILIENCE lunar lander

Although most spaceflight activity takes place in Low Earth Orbit (LEO, altitudes below approximately 1000 - 2000 km), recent years have seen an increase in deep space missions beyond this region, including to the Moon, cis-lunar space, and regions beyond. The deep space environment poses many challenges for human and robotic exploration, including stronger ionizing radiation fluxes, more extreme temperature variations, as well as limited data downlink volume. With the growth of flight opportunities to deep space aboard government and commercial lunar missions, characterizing the radiation environment and its effects on electronics during these missions is of critical importance for both crewed and uncrewed missions. Utilizing one of the growing number of rideshare opportunities offered by commercial lunar mission providers, we have completed the rapid development and deployment of a Deep Space Radiation Probe (DSRP), which was launched aboard the HAKUTO-R Mission 2 (M2) RESILIENCE lunar lander from ispace, inc. on January 15, 2025, immediately commencing operations following launch. Mounted on the exterior of the lander with minimal shielding, DSRP measured the accumulated radiation dose, dose rate, and single event upset (SEU) rate throughout the five-month mission, including multiple passes through the radiation belts, at distances far beyond the Moon, as well as in lunar orbit, being active for over 97% of the five-month mission, which was considerably longer than most other recent commercial lunar lander missions. The highest measured radiation dose rates are considerably larger than those aboard past lunar missions during lower solar activity levels, oftentimes inside shielded spacecraft. Passage through the radiation belts and solar radiation storms were correlated with increases in dose rate. On the other hand, bit flips caused by single event upsets (SEUs) that can result in data corruption and flight software malfunction were detected throughout the course of mission, not solely during solar radiation storms, suggesting galactic cosmic rays as the primary cause. A steady background deep space dose rate was also observed during quiet times due to galactic cosmic rays. The radiation data provided by DSRP with its unusually long mission duration will be beneficial for the development of future spacecraft electronics and crewed missions to deep space and the Moon, especially considering the long duration habitation plans of lunar exploration programs such as Artemis.