Analysis of Cluster spacecraft potential during active control

The floating potential of a spacecraft is determined by an equilibrium between photo-electron emission from the sunlit spacecraft surfaces and the plasma electron current, while other currents play a secondary role. On the Cluster spacecraft, the presence of the experiment ASPOC to control the potential by an ion beam with currents up to several tens of microamperes and energies of several keV provides an opportunity to study the interaction between the spacecraft and the ambient plasma with the current of the artificial ion beam as an additional parameter. The effect of active control on the Cluster spacecraft potential in the various plasma environments is presented in an overall statistics. Changes of the potential resulting from switching the ion beam current to different levels serve to calibrate the density–potential relationship.