Abstract
The Van Allen Probes Mission consists of two identical spacecraft flying
in highly elliptical orbits, with perigee altitudes originally near 600
km. During the low altitude periods of the orbits, the spacecrafts are
immersed in a region of high-density atomic Oxygen. Atomic Oxygen is
known to change and degrade the properties of spacecraft surfaces, such
as those of the Van Allen Probes Electric Field and Waves (EFW)
instrument. The consistency of the sensor surfaces in EFW is important
because the mechanisms used to ensure the collection of high quality
electric field measurements requires that the photoemission properties
of each sensor are uniform and stable. Oxidation or erosion of the
sensor surfaces could limit the instrument’s ability to balance the
currents produced by both the plasma electrons and the controlled bias
current applied to the sensors, and thus to properly operate the device.
We have modeled the atomic Oxygen exposure to the spacecraft to help
determine the impact it has had on the sensors. We have calculated the
fluence (time integrated flux) of atomic Oxygen particles that have
collided with the spacecrafts over the entire course of the mission. We
have also looked at the distribution of atomic Oxygen flux over time to
further analyze malfunctions in the sensor readings at different points
along the course of the mission. Additionally, we have investigated how
different surfaces of the spacecraft are affected differently due to
their orientation with respect to the spacecraft’s motion.