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 (as of Dec 2019) 2218 operational satellites in Earth orbit, of which 1468 are in low Earth orbit (LEO), 562 in geosynchronous orbit (GEO), 132 in medium Earth orbit (MEO), and 56 in elliptical orbit. Most are exposed to energetic electrons for at least some of their orbit. In 2018 the total global revenues from the satellite industry were US $277B, 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 are 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 in dialogues with clients and in the evaluation of 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
The award recognises Professor Horne’s unique ability to combine basic and applied research to develop useful space weather products.
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, medium and high 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]. This important result allows spacecraft operators to better trade-off risk versus the increased cost of protecting future satellites from worst-case conditions.
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 fluxes of E > 30keV and E > 300keV electrons, responsible for surface and internal charging respectively, in LEO as a function of orbital position [Meredith et al., 2016a]. This work extends the scope beyond the GEO regime to LEO (and potentially low-MEO) where the future large satellite constellations such as SpaceX Starlink and Oneweb are expected to operate.
the 1 in 100 year internal charging currents behind 0.5mm (typical for lightly shielded cables) and 1.5mm of aluminium (typical for better protected equipment within the body of the spacecraft) shielding in MEO is 2.4 and 1.6 times the current NASA guidelines for safe levels of operation respectively [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 but is increasingly used operationally, 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 100 year flux of relativistic electrons at geosynchronous orbit [Meredith et al., 2015], the location of the major telecommunications satellites, has had an immediate impact. The revised value, which is seven times that estimated from an earlier study, has been:
used by the Met Office to update the UK Cabinet Office and National Security Risk Assessment in 2017.
included in the US Space Weather Phase 1 Benchmarks produced by the Space Weather Operations, Research, and Mitigation Subcommittee of the US National Science and Technology Council.
used by a major satellite operator to improve the definition of spacecraft technical requirements and in the evaluation of satellite proposals received from manufacturers.
used by a major insurance consortium in dialogues with 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].
More generally, the 1 in 100 year event levels in LEO, MEO, GEO and HEO, as a function of electron energy, serve as space weather benchmarks. In particular:
they are being used in the revision of the UK National Risk Assessment.
they are being used by satellite operators to provide feedback to satellite manufacturers based on the on-orbit performance of their products.
they are being used by satellite operators and satellite equipment manufacturers for the purposes of situational awareness, operational risk assessments and post event analysis.
they are being used by a leading insurance underwriter to support space Realistic Disaster Scenarios.
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.
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