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 (Banks et al., 2004), 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 understand the potential 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.
Bibliographical noteFunding Information:
The authors thank the scientists and engineers associated with the EFW instrument for providing the high-quality data reported in this paper. They are also thankful to the developers of the NRLMSISE-00 Python package (Joshua Milas, available at https://github.com/DeepHorizons/Python-NRLMSISE-00) and the HWN93 Python package (Michael Hirsch, available at https://github.com/space-physics/hwm93). The work by the EFW team was conducted under NASA contract NNN06AA01C.
- atomic oxygen
- Langmuir probes
- Van Allen Probes