The twin drivers of globalisation and technological advance have created a developed and developing world that is increasingly dependent on satellite technology for communication, navigation, Earth observation and military surveillance. This growing infrastructure is vulnerable to the damaging effects of space weather.
The concern is such that governments around the world now regard extreme space weather as a potential emergency situation, and it is included in the UK’s National Risk Register of Civil Emergencies.
Space weather hazard
Energetic electrons are an important space weather hazard. They affect satellites in two principle ways. Electrons with energies in the range from ∼keV to ∼100 keV, which are injected during substorms, affect the current balance to the satellite surface. This may result in a high level of surface charging. Higher-energy electrons, known “killer” electrons, which tend to build up during geoeffective geomagnetic storms and high speed solar wind streams, can penetrate surface materials and embed themselves within insulators. Such charging is known as internal charging. Both surface charging and internal charging can lead to the build-up of significant amounts of charge, the subsequent discharge of which can damage components.
“Killer” electrons are found in two regions of near-Earth space – referred to as the inner and outer radiation belts. The inner radiation belt, which typically occurs at altitudes between 650 and 6500 km in the magnetic equatorial plane, is relatively stable. In sharp contrast, the outer radiation belt, which typically occurs at altitudes between 13,000 and 40,000 km, is highly dynamic with fluxes changing by orders of magnitude on timescales ranging from minutes to days. Substorm injected electrons tend to occupy roughly the same region as the outer radiation belt, but in contrast to the “killer” electrons, they are restricted in local time, ranging from the early evening sector through midnight to noon.
Risk to satellites
There are currently 1738 operational satellites in Earth orbit, of which 1071 are in low Earth orbit (LEO), 531 in geosynchronous orbit (GEO), 97 in medium Earth orbit (MEO), and 39 in elliptical orbit. Most are exposed to energetic electrons for at least some of their orbit. In 2016 the total global revenues from the satellite industry were US $260B, showing the importance of the industry to the economy. Extreme space weather events have a real capacity to damage this infrastructure, as happened during a major storm in 2003, when 10% of the satellite fleet experienced anomalies and one satellite (the joint Japanese/US Midori 2 satellite, costing US $640M) was a total loss.
Mitigating the risks
Our research seeks to determine the conditions that would occur in a 1 in 100 year-event to determine the likely impact of an extreme event. The severity of any given event depends on both location and electron energy. To understand this, and provide the information that the satellite industry needs, we conduct independent analyses for different electron energies and orbit types. The findings may be used by satellite operators and engineers to mitigate the risks to new satellites by improving the definition of spacecraft technical requirements and in the evaluation of satellite proposals received from manufacturers.
Modern satellites in medium Earth orbit and at geosynchronous orbit have life expectancies of 10-20 years. Satellite operators and engineers thus need realistic estimates of the flux levels that may be reached on these and longer timescales in order to assess the likely impact of an extreme event on the satellite fleet and to improve the resilience of future satellites by better design of satellite components. Satellite insurers also require this information to help them evaluate realistic disaster scenarios.
The overall aim of these studies is to determine the 1 in 10, 1 in 50, 1 in 100 and 1 in 150 year energetic electron flux levels as a function of energy for various key orbits and locations in near Earth space.
The 1 in 100 year event levels can be used as space weather benchmarks as defined by the Space Weather Operations, Research and Mitigation Subcommittee of the National Science and Technology Council
The benchmarks can be used to
determine the likely impact of an extreme event
improve the resilience of future satellites
evaluate potential disaster scenarios
The benchmarks may also be used for
comparison with ongoing events
the purposes of situational awareness and operational risk assessments
comparison with theoretical maximum fluxes
This work is aligned with the Industrial Strategy challenge for Satellites and Space Technology
Determination of the 1 in 100 year space weather event
In recent studies, as part of the EU FP7 project SPACESTORM, we used a branch of statistics, known as extreme value theory, to determine the 1 in 10, 1 in 50, 1 in 100 and 1 in 150 year space weather events for low and medium Earth orbit and geosynchronous orbit.
Our principle findings are:
the 1 in 100 year flux of E > 2 MeV electrons at geosynchronous orbit is seven times larger than previous estimates [Meredith et al., 2015]
the largest flux of E > 2 MeV electrons observed at geosynchronous orbit in a 20 year period (January 1995 to June 2014) is estimated to be a 1 in 50 year event. During the enhanced fluxes associated with this extreme event, the geosynchronous satellite Galaxy 10R lost its secondary ion propulsion system reducing its lifetime significantly and resulting in an insurance payout of US$75.3 million [Meredith et al., 2015]
the determination of the 1 in 100 year flux of E > 30 keV electrons, responsible for surface charging, in low Earth orbit as a function of orbital position [Meredith et al., 2016a]
the determination of the 1 in 100 year flux of E > 300 keV electrons, responsible for internal charging, in low Earth orbit as a function of orbital position [Meredith et al., 2016a]
the 1 in 100 year internal charging current behind 0.5 mm of aluminium shielding in medium Earth orbit is 2.4 times the current NASA guidelines for safe levels of operation [Meredith et al., 2016b]
the 1 in 100 year internal charging current behind 1.5 mm of aluminium shielding in medium Earth orbit is 1.6 times the current NASA guidelines for safe levels of operation [Meredith et al., 2016b]
the determination of the energy spectra, essential for the calculation of radiation effects on satellite components, of the 1 in 100 year relativistic electron fluxes throughout the Earth’s outer radiation belt from 0.69 to 2.05 MeV [Meredith et al., 2017]
the 1 in 100 year flux of relativistic electrons at equatorial medium Earth orbit, a region that had previously been poorly characterised, is a factor of 3 to 4 times larger than that at geosynchronous orbit, depending on energy [Meredith et al., 2017]
The determination of the 1 in N year fluxes of relativistic electrons at geosynchronous orbit [Meredith et al., 2015], the location of the major telecommunications satellites, have had an immediate impact. The values have been:
used to update the UK Cabinet Office and National security and intelligence National Risk Assessment 
included in a summary of space weather worst case environments compiled by the Chair of the UK Space Environment Impact Experts Group (SEIEG), to provide advice to the UK government to support the UK National Risk Register 
included in the US Space Weather Phase 1 Benchmarks draft report  produced by the Space Weather Operations, Research, and Mitigation Subcommittee of the US National Science and Technology Council. This council, which coordinates science and technology policy in the US, is chaired by the US President
used by a major global satellite operator to improve the definition of spacecraft technical requirements and in the evaluation of satellite proposals received from manufacturers
used by a leading insurance underwriter and its clients to assess if the latter are doing all they can to reduce risk
used by developers and insurers for comparison with theoretical maximum fluxes that might be expected based on physical principles, both as a test of theory and to gain confidence in predictions that have not been observed yet [e.g., Horne et al., 2018; Glauert et al., 2018]
used by engineers to determine the radiation effects of extreme space weather events on satellites [e.g., Hands et al., 2018]
Glauert, S. A., R. B. Horne and N. P. Meredith, A 30-year simulation of the outer electron radiation belt, Space Weather, doi:10.1029/2018SW001981, 2018.
Hands, A. D. P., K. A. Ryden, N. P. Meredith, S. A. Glauert, and R. B. Horne, Radiation effects on satellites during extreme events, Space Weather, doi:10.1029/2018SW001913, 2018.
Horne, R. B., M. W. Phillips, S. A. Glauert, N. P. Meredith, A. D. P. Hands, K. A. Ryden, and W. Li, Realistic worst case for a severe space weather event driven by a fast solar wind, Space Weather,doi:10.1029/2018SW001948, 2018.
Meredith, N.P., R. B. Horne, I. Sandberg, C. Papadimitriou and H. D. R. Evans, Extreme relativistic electron fluxes in the Earth’s outer radiation belt: Analysis of INTEGRAL IREM data, Space Weather, 15, 917-933, doi:10.1002/2017SW001651, 2017.
Meredith, N. P., R. B. Horne, J. D. Isles, K. A. Ryden, A. D. P. Hands and D. Heynderickx, Extreme internal charging currents in medium Earth orbit: Analysis of SURF plate currents on Giove-A, Space Weather, 14, 578-591,doi: 10.1002/2016SW001404, 2016.
Meredith, N. P., R. B. Horne, J. D. Isles, and J. C. Green, Extreme energetic electron fluxes in low Earth orbit: Analysis of POES E > 30, E > 100 and E > 300 keV electrons, Space Weather, 14,136-150,doi: 10.1002/2015SW001348, 2016.
Meredith, N. P., R. B. Horne, J. D. Isles, and J. V. Rodriguez, Extreme relativistic electron fluxes at geosynchronous orbit: Analysis of GOES E > 2 MeV electrons, Space Weather, 13, 170–184,doi: 10.1002/2014SW001143, 2015.