Space Weather Effects on Satellites

Introduction

Satellites are operating in an environment populated with charged particles. These particles can affect satellites in a variety of ways, either directly by penetrating into the satellite electronics, or indirectly through spacecraft charging with the resulting discharge causing problems. These processes can result in phantom commands, damage to electronics, loss of control, and even satellite failure.

Picture of a geostationary satellite above the Earth with a solar flare proton coming towards the satellite.

Solar Proton Effects

When high velocity ions plough through semiconductor devices they produce a large number of electrons and holes that carry currents within these devices. Large numbers of electron-hole pairs introduced into sensitive regions like memory cells can alter information and result in phantom commands. Effects can be devastating if ion impacts occur in control systems or decision-making circuits. In addition, these impacts degrade semiconductor lifetimes.

Picture of the inside of an integrated circuit showing the N-type and P-type semiconductor material.  Also shown is the trajectory of single fast moving ion that has created extra charges inside the semiconductor layers that disrupt that operation of the circuit.

Surface charging

Surface charging of spacecraft in synchronous orbit can occur due to incidence of a large incoming flux of electrons in the absence of sufficient charge drainage by mechanisms such as photoemission. "Hot" electrons with energies in the range of several to several tens of keV are mainly responsible for surface charging. Intense fluxes of these electrons are closely related to substorm activities, hence surface charging occurs more often in the midnight to dawn sector. The differential charging of spacecraft surfaces can give rise to destructive arc discharges, causing satellite operational anomalies.

Internal Charging

The occurrence of highly energetic (relativistic) electrons with energies greater than 2 Mev represents adverse space weather conditions hazardous for geosynchronous satellites. When this happens, there is a high likelihood of internal charging of satellite components by energetic electrons, with possible electric discharges that could result in malfunction or even complete failure of the satellite. Such an event was the likely cause of a number of satellite operational anomalies in January 1994.

A graph showing the energetic electron flux at geostationary orbit from January 10 to January 24, 1994.  Peaks in the electron flux on January 16, January 18, and January 20 coincide with satellite anomilies on the 505, 504, K, E1, and E2 satellites.

Electrostatic discharge

Electrostatic discharge results from spacecraft charging, be it surface or internal. Once the generated electric field due to charging exceeds a certain threshold, an arc discharge occurs, generating an electromagnetic transient that couples into spacecraft electronics and causes spacecraft operational anomalies. The following figure shows the local time distribution of occurrence of discharges.

A polar plot showing the occurence of static discharges on satellites as a function of local time. The occurence of discharge is greatest in the afternoon and evening sectors.