Note on the Pantellini et al. process for dust impact signals on spacecraft

In some recent papers it has been proposed that thick antennas are much more sensitive for the detection of dust impacts than thin wire antennas. This proposal attributes a large part of the signal on the antenna to a disruption of the photoelectron cloud around the antenna, and the signal is larger on thick antennas because there are more photoelectrons. However, comparison of thick and thin wire antennas on the Wind spacecraft has shown that thick antennas are somewhat more sensitive than thin wire antennas, but the difference is not as great as first supposed. Here an attempt is made to understand the quantitative difference between the responses of thick and thin antennas. It is found that a recent conjecture by the present author that the necessary increase in angular momentum for photoelectrons to avoid returning to a thick antenna would compensate for the larger number of photoelectrons is not correct. It is shown, however, that there is a significant difference in sensitivity between thin and thick antennas. An accurate calculation of the antenna sensitivities is not done here, as it depends on a number of factors, including a large difference in electric field around the antennas. Nevertheless, the photoelectron disruption mechanism is an important advance in understanding the coupling of dust impacts to antennas.