  There has been important understanding of the process by which a hypersonic
dust impact makes an electrical signal on a spacecraft sensor, leading to a
fuller understanding of the physics. Zaslavsky (2015) showed that the most
important signal comes from the charging of the spacecraft, less from charging
of an antenna. The present work is an extension of the work of Zaslavsky. An
analytical treatment of the physics of a hypersonic dust impact and the
mechanism for generating an electrical signal in a sensor, an antenna, is
presented. The treatment is compared with observations from STEREO and Parker
Solar Probe. A full treatment of this process by simulations seems beyond
present computer capabilities, but some parts of the treatment can must depend
on simulations but other features can be better understood through analytical
treatment. Evidence for a somewhat larger contribution from the antenna part of
the signal than in previous publications is presented. Importance of
electrostatic forces in forming the exiting plasma cloud is emphasized.
Electrostatic forces lead to a rapid expansion of the escaping cloud, so that
it expands more rapidly than escapes, and frequently surrounds one or more
antennas. This accounts for the ability of dipole antennas to detect dust
impacts. Some progress toward an understanding occasional negative charging of
an antenna is presented, together with direct evidence of such charging. Use of
laboratory measurements of charge to estimate size of spacecraft impacts are
shown to be not reliable without further calibration work.

Space Physics