Juice? No charge

Samples of the multi-layer insulation and coatings planned to cover the skin of ESA’s Juice spacecraft were subjected to a beam from the electron gun anchored at the top of this Electrostatic Discharge chamber before being selected for the mission to Jupiter.

Space might be a vacuum, but it is far from empty. Once ESA’s Juice spacecraft embarks on its eight-year journey to Jupiter, encounters with charged particles and radiation can gradually build up electrostatic charges across its surfaces. These in turn could perturb the mission’s instruments to measure the electromagnetic and plasma environment surrounding the spacecraft.

Some charging buildup is inevitable but in particular mission designers wished to avoid differential charging across the spacecraft: as well as disturbing instrument readings these might even in the worst case trigger damaging ‘electrostatic discharge’, resembling space lightning.

Accordingly all the surface layers of the Juice spacecraft have been designed to be as conductive as possible, to prevent any buildup of charge. But the sustained low temperatures of the Jupiter system, coupled with ageing effects, has the potential to increase resistance of materials over time, making charge accumulations more likely.

The ESD Chamber, part of ESA’s Materials and Electrical Components Laboratory at ESTEC in the Netherlands, was therefore used to test the charging properties of candidate materials. Its interior can be pumped down to a space-quality vacuum and it incorporates a liquid nitrogen cryogenic shroud to take temperatures down to -150°C. Test samples are placed on a baseplate whose temperature can be controlled down to -240°C.

Charging investigations were carried out on multi-layer insulation, candidate coatings and also the treated cover glass of solar panels, checking in particular how charging properties changed with temperature.

For more information on how the Juice mission was kept ‘clean’ in terms of electromagnetism and plasma buildups, click here.