Galactic Cosmic Ray Integral Flux Measurements in Lunar Orbit with CRaTER During the Deepest Solar Minimum of the Space Age

We report measurements of increasing intensities of galactic cosmic ray protons and helium ions from 2015 to the end of 2018. The overall decrease in solar activity in this period has led to an increased flux of galactic cosmic rays, to levels that are approaching those observed during the previous solar minimum in 2009/2010, which was the deepest minimum of the Space Age. The data have implications for human exploration of deep space and provide useful benchmarks for models of cosmic ray fluxes as a function of solar modulation.