Component Failures and Anomalies
4
H|0|star|star tracker|182|193|
G|0|ed|electrostatic discharge|243|265|
G|0|radiation|radiation|304|312|
G|0|proton|protons|841|847|
    Of the thousands of components aboard TOPEX/Poseidon, the only outright failures have been a few minor status indicators, external temperature sensors, and the disabling of one star tracker. Most of these failures have been attributed to electrostatic discharge through electronic components and to radiation. None have significantly impacted the spacecraft or its performance. The main effect of these failures is that component redundancy has been reduced. This limits options for work-arounds for possible failures in the future. 
    One phenomenon observed aboard the spacecraft is the Single-Event Upset, or SEU, in which single bits in semiconductor memories are changed. SEUs occur at random and with no warning, and affect memories and processors in many systems of the spacecraft. SEUs are caused by collisions of high-energy protons with semiconductor elements, and are geographically correlated with the South Atlantic Anomaly, an area known for a high density of energetic protons. SEUs are corrected automatically by memory-refresh programs, or through ground based intervention. To date, all affected systems have recovered from SEUs with no ill effects.
