Ilkka Sillanpaa

Oxygen ions at Titan's exobase in a Voyager 1–type interaction from a hybrid simulation

the conditions during the Voyager 1 flyby. Our model shows that the ionotail and the magnetotail bend in a direction opposite to the convection electric field. This is validated with the total force on the incident flow species derived from basic plasma equations. We also present a simulated impact map for the oxygen ions of the flow with total O + precipitation rate 1.3 � 10 24 s � 1 at Titan’s exobase. Although this rate indicates that the plasma conditions above the exobase do not inhibit O + precipitation on the exobase, the direction of the O + flow is shown to turn drastically near the exobase. The energy deposition of the medium-weight flow ions (such as O + ) thus seems to be orders of magnitude larger than the energy deposition by pickup ions formed near Titan. However, the lightweight flow ions (H + ) are effectively deflected by the magnetic barrier formed around Titan.

Spacecraft surface charging induced by severe environments at geosynchronous orbit

Severe and extreme surface charging on geosynchronous spacecraft is examined through the analysis of 16 years of data from particles detectors on-board the Los Alamos National Laboratory spacecraft. Analysis shows that high spacecraft frame potentials are correlated with 10 to 50 keV electron fluxes, especially when these fluxes exceed 1 × 108 cm−2 s−1 sr−1. Four criteria have been used to select severe environments: 1) large flux of electrons with energies above 10 keV, 2) large fluxes of electrons with energies below 50 keV and above 200 keV, 3) large flux of electrons with energies below 50 keV and low flux with energies above 200 keV, and 4) long periods of time with a spacecraft potential below - 5 kV. They occur preferentially during either geomagnetic storms or intense isolated substorms, during the declining phase of the solar cycle, during equinox seasons and close to midnight local time. The set of anomalies reported in Choi et al. (2011) is concomitant with a new database constructed from these events. The worst-case environments exceed the spacecraft design guidelines by up to a factor of 10 for energies below 10 keV. They are fitted with triple Maxwellian distributions in order to facilitate their use by spacecraft designers as alternative conditions for the assessment of worst-case surface charging.