Comparison of Solar Energetic Particle Flux Measurements by CRaTER and GOES

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Abstract
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–October 2024 time frame in which the integral flux of protons with energies greater than 100 MeV exceeded 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.
Funding Information
  • Johnson Space Center
  • National Aeronautics and Space Administration

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