Abstract-The Galileo global navigation system will employ an array of satellites in medium Earth orbit (MEO). Internal charging is one of the primary hazards for any spacecraft in MEO, and accordingly, the Galileo test satellite, Giove-A, carries a detector, SURF, to undertake the measurement of internal charging currents at three different shielding depths. The currents are due to electrons stopped in three aluminum plates: the first plate is 0.5 mm thick and located under 0.5-mm Al-equivalent shielding, the second is 0.5 mm thick and located underneath the first plate, and the third is 1.0 mm thick and located underneath the second plate. Giove-A was successfully launched on December 28, 2005 into a 23 300-km circular 56• inclination orbit. In this paper, we provide data on the internal charging currents observed in 2006, with particular emphasis on two large charging events, one in mid-April and one in mid-December. Comparisons are made to predictions using the DICTAT internal charging tool and the FLUMIC "worst case" trapped electron belt model. In general, the charging currents observed are safely within the standard DICTAT 3.5/FLUMIC 3.0 predictions but are exceeded in the most shielded plate on five calendar days during December 2006. The December event was unique in 2006 in that it was triggered by the arrival of a coronal mass ejection (CME) rather than being due to the effects of a fast solar wind stream flowing from a coronal hole. The currents measured in the December event were, however, an order of magnitude lower than those predicted using the "anomalously large event" supplement to FLUMIC which models the most extreme electron enhancements associated with CMEs. Index Terms-Energetic electron belts, internal charging, medium Earth orbit (MEO).

The radiation monitors on board the Galileo Giove-A satellite, CEDEX and Merlin, and their data are presented. The instruments include energetic proton and ion detectors, an internal charging monitor, RADFETs and experimental dose-rate photodiodes. A comparison of the data with existing monitors and models is presented.

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Abstract-Two new, miniaturised scientific radiation monitoring payloads are presented prior to their first flight on the TechDemoSat-1 Spacecraft. They are capable of monitoring the space radiation environment and its effects on radiation sensitive devices. MuREM and SSTL RM carry RADFET dosimeters, dose rate sensitive photodiodes and PIN diode particle detectors. SSTL RM is also connected to external RADFET sensors placed around the spacecraft, whilst MuREM carries a radiation effects payload consisting of COTS devices which will be monitored whilst exposed to the space radiation environment.

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