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  • Satellite Effects of Space Weather
  • Satellites and spacecrafts
  • Single Event Upsets (SEUs)

Single Event Upsets (SEUs)

  • Single event upsets occur when a high-energy particle (>~50 MeV) penetrates spacecraft shielding and has the misfortune to hit a device in just the wrong way to cause disruption. This is generally a hit or miss situation. Effects can range from simple device tripping to component latch-up or failure. Particle bombardment of memory devices can also change on-board software through physical damage or through deposition of charge resulting in a "bit flip." There are two natural phenomena that cause this type of problem - Galactic Cosmic Rays (GCRs) and Solar Proton Events (SPEs). Galactic cosmic "rays" are actually particles, sometimes with high Z number (nuclear mass) and energies exceeding GeV levels. Fortunately, the flux of GCRs is relatively low so the resulting SEU rate is also low. GCR fluxes are highest by approximately 25% during solar minimum. It is at this time that the Sun expels little solar material and magnetic fields to detect the incoming GCRs prior to arrival at Earth. Solar Proton Events at Earth can occur throughout the solar cycle but are most frequent in solar maximum years. SPEs result from powerful solar flares with fast coronal mass ejections. During an SPE satellites experience dramatically increased bombardment by high-energy particles, primarily protons. Fluxes of particles with energies > 10 MeV, can reach 70,000 protons/cm2/sec/ster. SEU rates increase with high fluxes since there is a higher likelihood of impact with a sensitive location. High-energy particles reach Earth from 30 minutes to several hours following the initiating solar event. The particle energy spectrum and arrival time seen by satellites varies with the location and nature of the event on the solar disk.

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