To develop a miniaturised version of an ion emitter to mitigate spacecraft charging effects on plasma measurements for science missions.

Spacecraft potentials in the outer Earth magnetosphere may reach a few tens of volts positive and therefore severely perturb plasma particle and electric field measurements. Therefore, magnetospheric missions from ESA such as Cluster, but also from international partners such as Double Stars and MMS have relied on an ion emitting instrument, ASPOC (Active Spacecraft Potential Control), developed by IWF in Austria for lowering the positive potential down to a few Volts positive. The latter version of ASPOC flown on MMS consists of 2 pairs of instruments (to ensure symmetric emission) of 2.9 kg each and consuming up to 3.7 W. Future magnetospheric missions such would also benefit from such a device. A miniaturised version of an ion emitter (<1 kg) for scientific missions is foreseen to reduce embarkation constraints and allow more mass allocation to payload sensors and their electronics and maintain European leadership for such an instrument.