Dust detection by antenna instruments: the effect of impact location

Abstract:

Antenna instruments on space missions have been used for the detection of dust particles and characterize their populations. The antennas register transient electric signals generated by the expanding plasma cloud following a dust impact on the spacecraft body or the antenna. Given their larger impact-sensitive area, antenna dust detections are complementary to dedicated dust detectors and enable the characterization of particles with lower fluxes. The dust accelerator facility operated at the University of Colorado has been employed to investigate the physical mechanisms of antenna signal generation. We have carried out several experimental campaigns to characterize variation in dust impact waveforms associated with variables such as the dust material, impact speed, spacecraft potential, and impact location. Here we report a physical model that provides a good qualitative and quantitative description of the antenna waveforms recorded in laboratory conditions. The model is based on the separation of electrons from the ions in impact plasma, taking into account their different expansion speeds. The spacecraft floating potential affects the fraction of electrons and ions from the impact plasma that are collected by the spacecraft or escape. A combination of the net collected charge and the induced charge from the escaping electron/ion populations is responsible for generating a voltage difference that is measurable by the antenna. Fitting the model to waveforms measured in the laboratory provides parameters of the dust impact plasma cloud. This new in-depth understanding of the signal generation mechanisms will enhance the analysis of data collected by several missions, including Cassini, STEREO, Parker Solar Probe, and Solar Orbiter.