Long-Term Galactic Cosmic Ray Environment Response of Plasma Analyzers on High-Altitude Spacecraft

Abstract

The long-term galactic cosmic ray (GCR) environment response of the dosimeter and surface-charging monitors on two high-altitude satellites called F1 and F2 is analyzed. These satellites also host the National Aeronautics and Space Administration’s Two Wide-angle Imaging Neutral-atom Spectrometers. The trend of the GCR intensity with solar cycle from year 2006 through 2012 is estimated from in-situ Advanced Composition Explorer (ACE) and Ulysses data. The dosimeter average 25–45 MeV proton counts and the electron counts at apogee follow the expected GCR solar-cycle trend, but the best-fit variations are smaller than estimated from ACE heavy ion GCR data. The surface-charging monitor average minima ion counts at apogee on F1, one of the host spacecraft, are consistent with the solar-cycle variation of Ulysses proton GCR counts. Linear fits to the F1 surface-charging monitor response to the GCR environment that may be subtracted from the measured counts before conversion to particle fluxes are provided. A similar analysis is performed for the surface-charging monitor on F2, the second host spacecraft. The general trend of the F2 data is not consistent with the cosmic ray solar-cycle trend and is suggestive of microchannel plate degradation.