Internal Charge Estimates for Satellites in Low Earth Orbit and Space Environment Attribution

Space assets are continuously bathed by charged particles making their components susceptible to the effects of spacecraft charging. While their orbits are not embedded within the radiation belts, low earth orbiting assets with high inclinations do pass through the horns of these belts during each polar crossing, transiting through potentially dangerous charged particle populations many times per day. Occasionally, these low altitude horns include significant populations of energetic ~1 MeV electrons, which can penetrate typical spacecraft shielding and accumulate within dielectric materials and on ungrounded conductors, a process known as internal charging. The National Oceanic and Atmospheric Administration Polar Operational Environmental Satellites (POES) have experienced on-orbit anomalies in the boost voltage regulator (BVR) that is suspected to be associated with the accumulation and discharge of ~800 keV electrons. We have used observations from the Medium Energy Proton and Electron Detector (MEPED) instrument and a first principles model of charge accumulation [11] to develop estimates of electron internal charge (IC) accumulation over the lifetime of each POES and Metop spacecraft for a range of typical discharge time constants. With the advantage afforded by a larger database of anomalies, we are able to show that these BVR anomalies are generally not attributable in a simple way to the accumulation and subsequent discharge from >800 keV nor a higher fluence of lower energy >300 keV electrons. To the best of our knowledge, this paper presents the first long-term estimates of IC for spacecraft in highly inclined low earth orbits.