International Space Station Spacecraft Charging Environments: Modeling, Measurement, and Implications for Future Human Space Flight Programs

Spacecraft charging analysis and mitigation is an interdisciplinary subject combining aspects of electrostatics, plasma physics, ionizing radiation, and materials science, as well as electronic systems electromagnetic interference and compatibility (EMI/EMC) effects. Spacecraft charging hazards are caused by the accumulation of electrical charge on spacecraft and spacecraft components produced by interactions with space plasmas, energetic charged particles, and solar UV photons as well as spacecraft electrical power and propulsion systems operations. Spacecraft charging hazard effects include both hard and soft avionics and electrical power system anomalies and have led to the partial or complete loss of numerous spacecraft.

The International Space Station (ISS) orbital altitude and inclination (~400 km and 51.6 degrees) determines the dominant natural environment factors affecting ISS spacecraft charging: 1) high speed flight through the geomagnetic field and 2) electrical power system interaction with the cold, high-density ionospheric plasma. In addition ISS is exposed to energetic auroral electrons at high latitude.

In this paper we compare ISS spacecraft charging measurements with numerical modeling of ISS charging processes. ISS is a large metallic structure and flight through the geomagnetic field at orbital speed dominates ISS charging. Collection of ionospheric electrons by the large 160 V photo-voltaic arrays is the next largest contributor. Charging by auroral electrons is detectable but makes a relatively minor contribution. Finally, we report the observation of short duration (~ 1 sec) rapid charging peaks associated with shunt/un-shunt operations of the 160 V photo-voltaic arrays, a phenomena not predicted before flight.

ISS spacecraft charging environments are radically different from those encountered at higher altitudes in Earth’s magnetosphere, and in cis-Lunar space. We present a brief review of those charging environments and an assessment of the applicability of ISS spacecraft charging management and flight experience to future human spaceflight programs beyond LEO.