Modelling of SURF detector responses in mixed electron/proton environments
Hands, A; Ryden, K; Dyer, C; Ford, K
QinetiQ

Energetic electrons, and the charging currents which they produce, represent one of the primary hazards to spacecraft in the space radiation environment. Internal charging of materials leads to electrostatic discharge (ESD) events that can cause catastrophic damage to the on board electronics. QinetiQ has developed the Merlin radiation monitor, which contains a suite of instruments including the ‘SURF’ detector which measures internal charging currents at three different shielding depths. Using both experimental and simulation techniques we have modelled the response of SURF to both proton and electron radiation environments. Here we demonstrate that SURF is especially well-suited to measuring the electron environment in both the inner and outer Van Allen belts with only minor contamination from either trapped or solar protons, thus avoiding the problems experienced by other techniques such as particle counters. In addition we use SURF data from the flight of Merlin on Giove-A, a test-bed for the forthcoming Galileo constellation, to show how the trapped electron spectrum may be derived from the internal charging current measurements at different shielding depths. This technique provides valuable data for the future updating of trapped electron belt models such as AE8 and FLUMIC.