Satellites can be damaged by high energy charged particles in the Earth’s radiation belts and during solar energetic particle (SEP) events. Here we review the growing reliance on satellite services, new vulnerabilities to space weather, and previous events that have led to loss of service. We describe a new European system to forecast the radiation belts up to 3 h ahead, which has three unique features: first, it uses physics-based models, which include wave-particle interactions; second, it provides a forecast for the whole outer radiation belt including geostationary, medium, and slot region orbits; third, it is a truly international effort including Europe, United States, and Japan. During the 8–9 March 2012 storm and SEP event, the models were able to forecast the >800 keV electron flux to within a factor of 2 initially, and later to within a factor of 10 of the GOES data. Although ACE and GOES data became unreliable during the SEP event, the system continued forecasting without interruption using ground-based magnetometers. A forecast of the 24 h electron fluence >2 MeV is used to provide a risk index for satellite operators. We show that including wave-particle interactions for L* > 6.5 improves the agreement with GOES data substantially and that a fast inward motion of the magnetopause to L* < 8 is related to rapid loss of relativistic electrons at geostationary orbit. Thus, we suggest that better wave-particle models and better coupling between the solar wind and the models of the magnetopause and radiation belts should lead to better forecasting.
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