Dust Observations with Antenna and Faraday Cup Measurements.

We address the physics of dust impacts and its influence on detecting dust particles in space.Dust impacts onto spacecraft can be observed by detecting dust surface charge directly.They can also be detected by antenna instruments, because the impacts generatefree atoms, molecules and particulate fragments, most of them in a charged state.Depending on the spacecraft potential a fraction of the impact-generated charges arerecollected, and the antenna instruments can register a transient charging event,typically 100 microseconds long. The shape of the signal is set by to the formation ofthe impact cloud, the escape of electrons and ions, and a subsequent relaxation tothe equilibrium potential depending on the surrounding plasma environment. Weconsider this process of impact cloud generation, expansion, charge separation andre-collection that take place before the spacecraft potential reaches its equilibriumagain. We discuss typical pulse shapes observed with antennas in different plasmaconditions. This type of impact process is best described at high velocities (few10 km/s) where impact-generated charges exceed by far the dust charges. At lowimpact velocities, as e.g. on atmospheric rockets, the dust is also measured via itssurface charge with Faraday cups. We discuss secondary charging processes thatinfluence these measurements. This is the effort of a team at the International SpaceScience Institute, in ISSI Bern brings together researchers who are studying differentaspects of dust and dust impacts (http://www.issibern.ch/teams/physdustimpact/). [ABSTRACT FROM AUTHOR]