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).
Abslracl-Results are reporled from the first flight of SURF, a new instrument designed to measure electrostatic charging effects on satellites. Internal charging currents detected around the geostationary transfer orbit at two different shielding depths are presented in the form of pmfiies of deposited current agairst L Data is limited to three periads: l6*-17* November MOO, 21"-29* November ZOO0 and 21"-W" March 2001. Large temporal variations of (negative) charging currents within the wter wne have been observed ranging, at the peak of the belt, over two orders of magitude. Substantial internal charging currents are also observed within the inner wne, particularly on the less well shielded collector plate. The polarity of the inner belt charging currents is also negative showing the dominance of electron deposition: for the shielding depths used, proton currents are d N I a t e d to be small, even at the peak of the inner bell. The new data suggests that for the higher eledron energies (> 1 MeV), the inner belt is softer than currently madelled in AE-8.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.