Parker Solar Probe FIELDS instrument charging in the near Sun
environment: Part I - Computational Model
Abstract
The Spacecraft Interaction Plasma Software package (SPIS), a
three-dimension particle in cell (PIC) code, was used to model the
Parker Solar Probe (PSP) spacecraft and FIELDS instrument and their
interactions with the Solar wind. Our SPIS modeling relied on material
properties of new spacecraft materials that we had obtained in previous
work. The model was used to find the floating potentials of the
spacecraft and FIELDS antennas at different distances from the Sun (from
1AU to 0.046AU). We find the following results: At greater distances
from the Sun, the shadowed spacecraft charges negatively while the
illuminated Thermal Protection System (TPS) charges positive due to the
high resistance of the TPS Alumina shield at low temperatures. As the
spacecraft approaches the Sun, the temperature of the TPS increases, the
resistance between it and the spacecraft drops, and its photoemission
increases, driving the spacecraft more positive. At the same time, an
electrostatic barrier forms near the illuminated surface of the TPS and
reflects the photoelectrons back leading to negative charging of some
surfaces. The FIELDS antennas and shield also see this barrier forming
but on a smaller scale. The FIELDS antennas charge positively at all
distances modeled when no current bias is applied. Current biasing of
the antennas affects their floating potential.