Internal charging in MEO using the SURF sensor
Abstract
The SURF instrument is a shielded current sensor with fA/cm-2 sensitivity which measures the key space weather hazard of internal charging in a very direct fashion. One such sensor has been operating in a GPS-like medium earth orbit (MEO) on the Giove-A spacecraft for a full solar cycle with only a few interruptions. Using three stacked shielded plates we observe internal charging currents due to electron energies from about 500keV to >3MeV. These currents have been converted to differential fluxes using plate response functions alongside some assumptions about spectral shape. No dead-time corrections are required since there is no counting process involved. In addition there is negligible contamination from protons even during intense solar particle events. The simplicity of the instrument and careful reference irradiations before flight mean that the results are highly reliable. We will present data obtained over the solar cycle and review periods of particular interest including the electron desert period in 2009 and the recent upsurge in internal charging events in the decline from solar maximum. We also describe a new model of the outer belt, MOBE-DIC, which has been developed from the SURF data which is intended for engineering applications. Furthermore reference is made to an earlier data set from the very first SURF instrument in geostationary transfer orbit which found significant inner belt charging currents which is at odds with recent Van Allen Probes measurements from this region and thus that data might be more significant than first thought. Looking to the future a further SURF instrument should be launched on DSX in June 2018 so further results from MEO should soon be available.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E2925R