Observations of internal charging and outer-belt electron enhancements from Giove-A

The planned Galileo global navigation system will employ an array of satellites in medium Earth orbit. Internal charging is one of the primary hazards for any spacecraft in MEO and accordingly the Galileo test spacecraft, Giove-A, carries the dasiaSURFpsila detector to undertake measurements of internal charging currents deposited at three different shielding depths (0.5, 1.0 and 1.5 mm Al). Giove-A was successfully launched on 28th December 2005 into a 23,300 km circular, 56 degree inclination orbit. In this paper we provide data on the charging currents observed in 2006, with particular emphasis on two large charging events, one in April and one in December. Comparisons are made between the flight data and predictions made using ESA´s internal charging tool, DICTAT, which employs the FLUMIC dasiaworst casepsila electron belt model. The DICTAT predictions of charging current are exceeded for a few days in the 1.5 mm Al shielded plate in the course of the December event.