The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter spacecraft has been operating in lunar orbit since 2009. CRaTER data provide a long-term record of the near-Moon radiation environment that is relevant to human exploration. In considering requirements for operational instruments on crewed lunar missions that are anticipated in the next several years, the question arises whether real-time measurements by existing assets such as Geostationary Operational Environment Satellite (GOES) are adequate for providing radiation warnings for the safety of astronauts on or near the Moon during Energetic Solar Particle Events (ESPEs). ESPEs are distinguished from more typical Solar Particle Events (SPEs) by their large fluxes of higher-energy particles. Here we show direct comparisons of contemporaneous ESPE measurements made in the two locations to establish that the radiation environments in lunar space and in geostationary orbit (GEO) are sufficiently similar to allow the use of GOES as a warning system for crew on or near the Moon. The conclusion is based primarily on data from six ESPEs in the October 2021 to October 2024 time frame in which the integral flux of protons with energies greater than 100 MeV exceeded 1 cm$^{-2}$ sr$^{-1}$ s$^{-1}$ at the event’s peak as measured by operational GOES satellites, and to a lesser extent on data from two earlier ground-level events (GLEs) that are of particular interest. We report new methods for analyzing CRaTER data under high-flux conditions and find good agreement with data reported by GOES-16 and later satellites.

In addition to the omnipresent Galactic Cosmic Rays (GCRs), sudden solar energetic particle (SEP) events present considerable health hazards for manned space missions. These events not only contribute to an increased long-term cancer risk, but can, in extreme cases, cause acute radiation syndromes. Forecasting their imminent occurrence could significantly reduce radiation exposure by warning astronauts to move to shelter. However, all currently available tools are primarily designed for the Earth or Earth-Moon system, which limits their applicability to future Mars missions. To address this, we developed a nowcasting system for SEP events applicable in deep space and on the Martian surface, which serves as a reliable last-resort backup when forecasts fail. The methodology of this system is based on dose rates measured by the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL), which recorded 5 SEP events during the seven-month flight to Mars and 16 since its landing on Mars on August 6, 2012. An SEP event is triggered, and an astronaut is warned as soon as dose rates exceed the omnipresent background level by at least 25%. This approach suggests that our system can provide astronauts with at least 30 minutes to avoid both peak radiation exposure and the majority of the cumulative dose from SEP events. Our nowcasting system is robust, easily implementable in real-life scenarios, and achieves a near-zero false alarm rate both in deep space and on the Martian surface.