Interpreting Dust Impact Signals Detected by the STEREO Spacecraft

Abstract

There is no comprehensive understanding yet of how dust impacts on spacecraft (SC) generate signals detected by antenna instruments. The high sensitivity of the S/WAVES instrument and the large number and high diversity of dust impacts detected make the STEREO mission particularly well suited for a closer investigation. A floating perturbation model (FPP) was recently proposed to explain the characteristic shape of dust impact signals with an overshoot. The FPP model posits that the overshoot is due to the different discharge time constant of the SC and the individual antennas. Kinetic simulations are performed to demonstrate that, contrary to common belief, antennas are inefficient collectors of charged particles from impact plasmas. The collection efficiency is small, only 0.1–1%, varying weakly with the bias potential between the antenna and the SC, and more strongly with impact location. The low recollection efficiencies and an analysis of the shapes and scaling of typical and atypical signals recorded by S/WAVES suggest that, besides the mechanism described by the FPP model, there is another, possibly stronger mechanism that is responsible for generating the characteristic overshoot for most dust impact signals observed by STEREO.