Keith Ryden

Professor Keith Ryden


Reader in Space Engineering
PhD MSc BSc(Hons) CEng FIET
+44 (0)1483 682226
22 BA 01

Biography

Areas of specialism

Space Environment; Radiation Effects

Research

Research interests

Courses I teach on

Postgraduate taught

Undergraduate

My publications

Publications

A. D. P Hands, F Baird, K. A Ryden, C. S Dyer, F Lei, J. G Evans, J. R Wallbank, M Szczykulska, D Rylett, R Rosolem, S Fowler, D Power, E. M Henley (2021)Detecting Ground Level Enhancements Using Soil Moisture Sensor Networks, In: Space Weather19(8)e2021SW002800

Ground level enhancements (GLEs) are space weather events that pose a potential hazard to the aviation environment through single event effects in avionics and increased dose to passengers and crew. The existing ground level neutron monitoring network provides continuous and well-characterized measurements of the radiation environment. However, there are only a few dozen active stations worldwide, and there has not been a UK-based station for several decades. Much smaller neutron detectors are increasingly deployed throughout the world with the purpose of using secondary neutrons from cosmic rays to monitor local soil moisture conditions (COSMOS). Space weather signals from GLEs and Forbush decreases have been identified in COSMOS data. Monte Carlo simulations of atmospheric radiation propagation show that a single COSMOS detector is sufficient to detect the signal of a medium-strength (10%–100% increase above background) GLE at high statistical significance, including at fine temporal resolution. Use of fine temporal resolution would also provide a capability to detect Terrestrial Gamma Ray Flashes (via secondary neutrons) which are produced by certain lightning discharges and which can provide a hazard to aircraft, particularly in tropical regions. We also show how the COsmic-ray Soil Moisture Observing System-UK detector network could be used to provide warnings at the International Civil Aviation Organization “Moderate” and “Severe” dose rate thresholds at aviation altitudes, and how multiple-detector hubs situated at strategic UK locations could detect a small GLE at high statistical significance and infer crucial information on the nature of the primary spectrum.

Rémi Pacaud, Thierry Paulmier, Pierre Sarrailh, Keith Ryden, Alex Hands, Denis Payan (2019)Study of internal charging of four commonly used polymers through experimental and numerical analysis, In: Journal of Applied Physics125(4)045108pp. 045108-1 AIP Publishing

This paper focuses on the study of internal charging of four space used polymers: polyetheretherketone, fluorinated ethylene propylene, polyimide films, and epoxy based material (Epoxy FR4). Experiments were carried out for each material using the GEODUR facility (Toulouse, ONERA) that mimics the geostationary space environment behind shielding. Two different irradiation currents have been applied: 1 pA/cm2 and 10 pA/cm2. 1 pA/cm2 is used to analyze the charging behavior and the intrinsic electrical properties of each polymer. 10 pA/cm2 is used to study the influence of high electric field levels on their charging behavior. In this paper, two different numerical tools used for the study of internal charging are presented: Monte-Carlo Internal Charging Tool (MCICT) and Transport of Holes and Electrons Model under Irradiation in Space (THEMIS). MCICT has been used in the space community for several years. THEMIS has been recently developed at ONERA and is compared to MCICT. Both numerical tools showed consistent results for the 1 pA/cm2 integrated current but with deviations for the 10 pA/cm2 integrated current, supposedly due to nonlinear electric field effects on charge transport. THEMIS has a more refined physical model for the conductivity than MCICT. It studies more accurately the electron-polymer interactions and the charge transport kinetics of polymers under space radiations. Subsequently, the analysis of the underlying physical phenomena responsible for the polymers’ charging behaviors will be carried out with THEMIS. In addition, studying these phenomena will permit to assess the risks of electrical discharges that may occur on a spacecraft in orbit (e.g., Geostationary (GEO) spacecraft) or during an elliptic trajectory (e.g., sub-GEO) in an Electric Orbit Raising case [E. Y. Choueiri, A. J. Kelly, and R. G. Jahn, J. Spacecr. Rockets 30(6), 749–754 (1993)].

Keith Ryden, PA Morris, KA Ford, ADP Hands, CS Dyer, B Taylor, CI Underwood, DJ Rodgers, G Mandorlo, G Gatti, HDR Evans, EJ Daly (2008)Observations of Internal Charging in Medium Earth Orbit, In: IEEE Trans. Plasma. Sci36(5)pp. 2473-2481
CJ Mertens, GP Gronoff, RB Norman, BM Hayes, TC Lusby, T Straume, W Kent Tobiska, A Hands, KA Ryden, E Benton, S Wiley, B Gersey, R Wilkins, X Xu (2016)Cosmic Radiation Dose Measurements from the RaD-X Flight Campaign, In: Space Weather14(10)pp. 874-898

Abstract The NASA Radiation Dosimetry Experiment (RaD-X) stratospheric balloon flight mission obtained measurements for improving the understanding of cosmic radiation transport in the atmosphere and human exposure to this ionizing radiation field in the aircraft environment. The value of dosimetric measurements from the balloon platform is that they can be used to characterize cosmic ray primaries, the ultimate source of aviation radiation exposure. In addition, radiation detectors were flown to assess their potential application to long-term, continuous monitoring of the aircraft radiation environment. The RaD-X balloon was successfully launched from Fort Sumner, New Mexico (34.5°N, 104.2°W) on 25 September 2015. Over 18 hours of flight data were obtained from each of the four different science instruments at altitudes above 20 km. The RaD-X balloon flight was supplemented by contemporaneous aircraft measurements. Flight-averaged dosimetric quantities are reported at seven altitudes to provide benchmark measurements for improving aviation radiation models. The altitude range of the flight data extends from commercial aircraft altitudes to above the Pfotzer maximum where the dosimetric quantities are influenced by cosmic ray primaries. The RaD-X balloon flight observed an absence of the Pfotzer maximum in the measurements of dose equivalent rate.

Richard B Horne, Mark W Phillips, Sarah A Glauert, Nigel P Meredith, Alexander Hands, Keith Ryden, Wen Liu (2018)Realistic Worst Case for a Severe Space Weather Event Driven by a Fast Solar Wind Stream, In: Space Weather16(9)pp. 1202-1215 American Geophysical Union

Satellite charging is one of the most important risks for satellites on orbit. Satellite charging can lead to an electrostatic discharge resulting in component damage, phantom commands, and loss of service and in exceptional cases total satellite loss. Here we construct a realistic worst case for a fast solar wind stream event lasting 5 days or more and use a physical model to calculate the maximum electron flux greater than 2 MeV for geostationary orbit. We find that the flux tends toward a value of 106 cm−2·s−1·sr−1 after 5 days and remains high for another 5 days. The resulting flux is comparable to a 1 in 150‐year event found from an independent statistical analysis of electron data. Approximately 2.5 mm of Al shielding would be required to reduce the internal charging current to below the National Aeronautics and Space Administration‐recommended guidelines, much more than is currently used. Thus, we would expect many satellites to report electrostatic discharge anomalies during such an event with a strong likelihood of service outage and total satellite loss. We conclude that satellites at geostationary orbit are more likely to be at risk from fast solar wind stream event than a Carrington‐type storm.

B. J. Clewer, K. A. Ryden, A. C. R. Dyer, A. D. P. Hands, D. R. Jackson (2019)A Citizen Science Network for Measurements of Atmospheric Ionising Radiation Levels, In: Space Weather17(6)pp. 877-893 American Geophysical Union

Historically, gathering data on atmospheric radiation levels during solar particle events (SPEs) has been difficult, as there is little or no time warning of events. Being able to accurately quantify radiation levels within the atmosphere during solar events is of significance to the aviation industry, as described in the International Civil Aviation Organization's (ICAO) Space Weather manual, particularly during a large Ground Level Enhancement (GLE) where the ionising dose to passengers and crew can exceed the recommended general public annual dose limits, set by the International Commission for Radiological Protection (ICRP) Barlett, Beck, Bilski, Bottollier‐Depois, and Lindborg (2004), in one flight. The Smart Atmospheric Ionising RAdiation (SAIRA) Monitoring Network is a new system of handheld radiation detectors that can be carried on aircraft to monitor and record atmospheric radiation levels. The system operates via citizen science volunteers, who record radiation data as they travel for normal purposes. Over 30 flights have been conducted with volunteers to demonstrate that a citizen science network is possible. Volunteers have used a new Android application to record and upload data to a central server to form a database of flight measurements. The demonstration has shown there is a willingness in public volunteers to use radiation detectors and engage in science outreach. A fully developed system will ideally provide the capability to quantify radiation levels during a Solar Particle Event (SPE) or GLE and the data can be used by relevant organisations to minimise potential risks.

ADP Hands, Keith Ryden, NP Meredith, SA Glauert, RB Horne (2018)Radiation Effects on Satellites During Extreme Space Weather Events, In: Space Weather16(9)pp. 1216-1226 American Geophysical Union

High-energy trapped electrons in the Van Allen belts pose a threat to the survivability of orbiting spacecraft. Two key radiation effects are total ionizing dose and displacement damage dose in components and materials, both of which cause cumulative and largely irreversible damage. During an extreme space weather event, trapped electron fl uxes in the Van Allen belts can increase by several orders of magnitude in intensity, leading to an enhanced risk of satellite failure. We use extreme environments generated by modeling and statistical analyses to estimate the consequences for satellites in terms of the radiation effects described above. A worst-case event could lead to signi fi cant losses in power generating capability — up to almost 8% — and cause up to four years ’ worth of ionizing dose degradation, leading to component damage and a life-shortening effect on satellites. The consequences of such losses are hugely signi fi cant given our increasing reliance on satellites for a vast array of services, including communication, navigation, defense, and critical infrastructure.

A. D. P. Hands, H. Evans, K.A Ryden, I. Sandberg, D. Heynderickx, G. Provatas, S. Aminalragia-Giamini, A. Tsigkanos, C. Papadimitriou, D. Rodgers (2019)An Update to MOBE-DIC Using Current Monitor Measurements From Galileo, In: IEEE Transactions on Nuclear Science67(1)pp. 181-190 Institute of Electrical and Electronics Engineers

We use electron flux derived from the environment monitoring unit “(EMU)-SURF” current monitor on board a Galileo Global Navigation Satellite System (GNSS) constellation satellite to modify and update the model of outer belt electrons for dielectric internal charging (MOBE-DIC). We describe how this data set, together with data from similar current-measuring instruments on Van Allen Probes, Giove-A, and STRV1d, are used to improve and expand the model. We have extended the spatial range to include the inner belt, exploited EMU data to widen the energy range for the electron spectrum, updated the statistical analysis of flux variation using a data set double the size used for the original model, and established a new and independent latitude function that yields improved agreement in medium earth orbit compared to the original model. The model is entirely characterized by a set of equations and parameters that produce fluxes as a function of magnetic coordinates at three distinct statistical levels.

A Hands, P Morris, K Ryden, C Dyer, P Truscott, A Chugg, S Parker (2011)Single event effects in power MOSFETs due to atmospheric and thermal neutrons, In: IEEE Transactions on Nuclear Science58(6)pp. 2687-2694 IEEE

Eight commercially available n-channel power MOSFETs were exposed to high energy spallation neutrons and thermal neutrons in separate experiments. Single event burnout (SEB) was observed in several of the devices in both environments. Measurements of SEB at derated drain-source voltages show very strong reductions in burnout cross-sections, but suggest that current recommendations for safe operation of devices may need updating for high voltage devices. In one device a different failure mode was observed, with subsequent investigations suggesting that single event gate rupture (SEGR) was responsible. This first observation of SEGR in accelerated neutron testing of power MOSFETs represents a new consideration for designers of high voltage control systems. © 2011 IEEE.

A Hands, P Morris, C Dyer, K Ryden, P Truscott (2011)Single event effects in power MOSFETs and SRAMs due to 3 MeV, 14 MeV and fission neutrons, In: IEEE Transactions on Nuclear Science58(3)pp. 952-959

Various SRAM and MOSFET devices were exposed to 3 MeV and 14 MeV neutrons at a fusion facility and to a fission neutron spectrum with a californium-252 source. Single event burnout (SEB) was observed in several of the MOSFETs in all three environmentsthe first time this phenomenon has been observed at neutron energies below 10 MeV. In addition to observing single event upsets (SEU) and single event latchup (SEL) in the SRAMs, two devices experienced significant multiple cell upset (MCU) effects which dominated the upset rate. The physical mechanisms underlying these phenomena and the consequences for various radiation environments are discussed. © 2011 IEEE.

Keith Ryden, Alexander Hands (2017)Modelling of electric fields inside spacecraft dielectrics using in-orbit charging current data, In: IEEE Transactions on Plasma Science45(5) IEEE

Internal charging caused by energetic electrons is a recognized threat to critical space infrastructure such as navigation and communication satellites. In this paper the electric field developed inside selected on-board dielectrics over a 10-year period in a GPS-like orbit is modelled using actual charging currents measured directly in orbit. The charging currents provide both charge deposition and dose rate inputs to the model, the latter allowing the introduction of radiation induced conductivity (RIC) to improve realism. As expected we find that RIC is a mitigating factor for the electric fields but they can still become very large e.g. a 1.0 mm thickness of PEEK under 0.5mm of Al shielding would be at risk of breakdown almost throughout the mission. We also find that RIC tends to reduce sensitivity to space weather perturbations of the environment such as the April 2010 storm event. This seems physically reasonable but we also know that some satellite anomalies do correlate quite well with space weather and short term (daily) electron fluence increases. We recommend that correlation of anomaly data sets with electric field models of this type is undertaken in future: this will require accurate materials parameters and also needs to take account of sudden depletion of the electric field due to discharges. In addition more charging current sensors with greater shielding levels (>2mm Al equivalent) should be flown to allow modeling of a wider range of realistic cases, including inside well-shielded electronic boxes.

S Bourdarie, D Lazaro, A Hands, K Ryden, P Nieminen (2009)Electron environment specification models for navigation orbits, In: Proceedings of the European Conference on Radiation and its Effects on Components and Systems, RADECSpp. 364-368

Electron environment specification models have been developed to assess long term effects (e.g. doses) as well as short term effects (e.g. internal charging) for navigation orbiting spacecraft design. © 2009 IEEE.

A Hands, P Morris, K Ryden, C Dyer (2012)Large-scale multiple cell upsets in 90 nm commercial SRAMs during neutron irradiation, In: IEEE Transactions on Nuclear Science59(6)pp. 2824-2830

During neutron irradiation of 4-Mb SRAMs, large-scale multiple cell upsets (MCUs) were observed. These were observed in 90-nm devices at accelerated test facilities providing fission, fusion, and spallation neutron environments. The MCUs are shown to manifest themselves in 2-D patterns encompassing scores of cells, which, even with bit interleaving, lead to uncorrectable multiple bit upsets (MBU) in the same word. The mechanism behind the MCU appears to be micro-latching within blocks of the memory array that are powered up sequentially during the read cycle of the device. © 1963-2012 IEEE.

R Gowen, A Smith, B Winter, C Theobald, K Rees, AJ Ball, A Hagermann, S Sheridan, P Brown, T Oddy, M Dougherty, P Church, Y Gao, A Jones, KH Joy, I Crawford, T Pike, S Kumar, T Hopf, N Wells, K Green, Keith Ryden (2008)An update on MoonLITE, In: Proceedings of 59th International Astronautical Congress7pp. 4359-4369

MoonLITE is a proposed, UK led lunar science mission involving 4 scientific penetrators that will make in situ measurements at widely separated locations on the Moon. MoonLITE will create the first global lunar network with nodes near and far-side, and in permanently shaded crater(s). With such a network MoonLITE will be able to determine much about the interior of the Moon, including characterisation of its core. Penetrator(s) at the poles will seek and characterise frozen volatiles, possibly of cometary origin and of great importance both to human exploration and to astrobiology. MoonLITE penetrators will reach the Moon at ~300 m/s and so must be able to stand the forces associated with this impact. As part of a programme aimed to establish reliable penetrator technologies the first full-scale impact trials have been conducted and are described here.

I. Sandberg, S. Aminalragia-Giamini, G. Provatas, A. Hands, K. Ryden, D. Heynderickx, A. Tsigkanos, T. Papadimitriou, T. Nagatsuma, H. Evans, D. Rodgers (2019)Data Exploitation of New Galileo Environmental Monitoring Units, In: IEEE Transactions on Nuclear Science Institute of Electrical and Electronics Engineers (IEEE)

The radiation environment of the Galileo spacecraft is severe and poorly characterized. The Galileo orbit takes the spacecraft through the heart of the outer radiation belt, while the low levels of geomagnetic shielding throughout the orbit expose the spacecraft to intermittent intense fluxes of protons during Solar Energetic Particle Events. In the Galileo constellation, two Environmental Monitoring Units (EMU) are currently flying in two different orbital planes. These units monitor the radiation environment and provide critical information related to hazards for the host spacecraft and its payload. In this work, we present results from the analysis of the surface charge collecting plates and of the proton telescope sensors. The performed numerical calibration of the EMU sensors and the application of novel unfolding and in-flight cross-calibration techniques allow the calculation of high quality proton and electron differential fluxes. The creation of a high-quality, long-term EMU electron flux dataset, is a step forward towards the improved characterization of MEO environment through the update of existing or the development of new radiation environment models.

KA Ryden, PA Morris, Alexander Hands, R Rampini, D Rodgers (2012)Enhanced Experimental Facility to Study Internal Charging at Extremely Low Temperatures, In: Proceedings of 12th Spacecraft Charging Technology Conference
WK Tobiska, W Atwell, P Beck, E Benton, K Copeland, C Dyer, B Gersey, I Getley, A Hands, M Holland, S Hong, J Hwang, B Jones, K Malone, MM Meier, C Mertens, T Phillips, K Ryden, N Schwadron, SA Wender, R Wilkins, MA Xapsos (2015)Advances in Atmospheric Radiation Measurements and Modeling Needed to Improve Air Safety, In: SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS13(4)pp. 202-210 AMER GEOPHYSICAL UNION
KA Ryden, ADP Hands, CI Underwood, DJ Rodgers (2015)Internal Charging Measurements in Medium Earth Orbit Using the SURF Sensor: 2005-2014, In: IEEE TRANSACTIONS ON PLASMA SCIENCE43(9)pp. 3014-3020 IEEE
NP Meredith, RB Horne, JD Isles, KA Ryden, ADP Hands, D Heynderickx (2016)Extreme internal charging currents in medium Earth orbit: Analysis of SURF plate currents on Giove-A, In: Space Weather14 American Geophysical Union

Relativistic electrons can penetrate spacecraft shielding and can damage satellite components. Spacecraft in medium Earth orbit pass through the heart of the outer radiation belt and may be exposed to large fluxes of relativistic electrons, particularly during extreme space weather events. In this study we perform an extreme value analysis of the daily average internal charging currents at three different shielding depths in medium Earth orbit as a function of L∗ and along the orbit path. We use data from the SURF instrument on board the European Space Agency's Giove-A spacecraft from December 2005 to January 2016. The top, middle, and bottom plates of this instrument respond to electrons with energies >500 keV, >700 keV, and >1.1 MeV, respectively. The 1 in 10 year daily average top plate current decreases with increasing L∗ ranging from 1.0 pA cm−2 at L∗=4.75 to 0.03 pA cm−2 at L∗=7.0. The 1 in 100 year daily average top plate current is a factor of 1.2 to 1.8 larger than the corresponding 1 in 10 year current. The 1 in 10 year daily average middle and bottom plate currents also decrease with increasing L∗ ranging from 0.4 pA cm−2 at L∗=4.75 to 0.01 pA cm−2 at L∗=7.0. The 1 in 100 year daily average middle and bottom plate currents are a factor of 1.2 to 2.7 larger than the corresponding 1 in 10 year currents. Averaged along the orbit path the 1 in 10 year daily average top, middle, and bottom plate currents are 0.22, 0.094, and 0.094 pA cm−2, respectively.

Mike Hapgood, Matthew J Angling, Gemma Attrill, Mario Bisi, Paul S Cannon, Clive Dyer, Jonathan P Eastwood, Sean Elvidge, Mark Gibbs, Richard A Harrison, Colin Hord, Richard B Horne, David R Jackson, Bryn Jones, Simon Machin, Cathryn N Mitchell, John Preston, John Rees, Neil C Rogers, Graham Routledge, Keith Ryden, Rick Tanner, Alan W.P Thomson, James A Wild, Mike Willis (2021)Development of Space Weather Reasonable Worst Case Scenarios for the UK National Risk Assessment, In: Space Weather19(4)e2020SW002593 American Geophysical Union

Severe space weather was identified as a risk to the UK in 2010 as part of a wider review of natural hazards triggered by the societal disruption caused by the eruption of the Eyjafjallajökull volcano in April of that year. To support further risk assessment by government officials, and at their request, we developed a set of reasonable worst‐case scenarios and first published them as a technical report in 2012 (current version published in 2020). Each scenario focused on a space weather environment that could disrupt a particular national infrastructure such as electric power or satellites, thus, enabling officials to explore the resilience of that infrastructure against severe space weather through discussions with relevant experts from other parts of government and with the operators of that infrastructure. This approach also encouraged us to focus on the environmental features that are key to generating adverse impacts. In this paper, we outline the scientific evidence that we have used to develop these scenarios, and the refinements made to them as new evidence emerged. We show how these scenarios are also considered as an ensemble so that government officials can prepare for a severe space weather event, during which many or all of the different scenarios will materialize. Finally, we note that this ensemble also needs to include insights into how public behavior will play out during a severe space weather event and hence the importance of providing robust, evidence‐based information on space weather and its adverse impacts.

Gemma D. R Attrill, Andrew C Nicholas, Graham Routledge, Junayd A Miah, Dhiren O Kataria, Cathryn N Mitchell, Robert J Watson, James Williams, Alex Agathanggelou, Charles M Brown, Scott A Budzien, Tobias Carman, Rahil Chaudery, Kenneth F Dymond, Ted T Finne, Alex Fortnam, Bruce Fritz, Alex Hands, Peter J Marquis, Talini Pinto-Jayawardena, Sean Murphy, Duncan Rust, Keith A Ryden, Dave Schofield, Andrew W Stephan, Kevin Wiggins, Craig Underwood (2021)Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE), In situ and Remote Ionospheric Sensing (IRIS) suite, In: Journal of space weather and space climate11

The UK’s Defence Science and Technology Laboratory (Dstl) is partnering with the US Naval Research Laboratory (NRL) on a joint mission to launch miniature sensors that will advance space weather measurement and modelling capabilities. The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) comprises two 6U cube-satellites that will be launched into a near-polar low earth orbit (LEO), targeting 500 km altitude, in 2021. The UK contribution to CIRCE is the In situ and Remote Ionospheric Sensing (IRIS) suite, complementary to NRL sensors, and comprising three highly miniaturised payloads provided to Dstl by University College London (UCL), University of Bath, and University of Surrey/Surrey Satellite Technology Ltd (SSTL). One IRIS suite will be flown on each satellite, and incorporates an ion/neutral mass spectrometer, a tri-band global positioning system (GPS) receiver for ionospheric remote sensing, and a radiation environment monitor. From the US, NRL have provided two 1U Triple Tiny Ionospheric Photometers (Tri-TIPs) on each satellite (Nicholas et al., 2019), observing the ultraviolet 135.6 nm emission of atomic oxygen at night-time to characterize the two-dimensional distribution of electrons.

Alexander Hands, F Lei, Keith Ryden, C Dyer, Craig Underwood, C Mertens (2016)New Data and Modelling for Single Event Effects in the Stratospheric Radiation Environment, In: IEEE Transactions on Nuclear Science64(1)pp. 587-595 IEEE

The upper atmosphere is a transition region between the neutron-dominated aviation environment and satellite environment where primary protons and ions dominate. We report high altitude balloon measurements and model results characterising this radiation environment for single event effects (SEE) in avionics. Our data, from the RaySure solid-state radiation monitor, reveal markedly different altitude profiles for low linear energy transfer (LET) and high LET energy depositions. We use models to show that the difference is caused by the influence of primary cosmic ray particles, which induce counts in RaySure via both direct and indirect ionization. Using the new Model of Atmospheric Ionizing Radiation Effects (MAIRE), we use particle fluxes and LET spectra to calculate single event upset (SEU) rates as a function of altitude from ground level to the edge of space at 100 km altitude. The results have implications for a variety of applications including high altitude space tourism flights, UAVs and missions to the Martian surface.

Alex Hands, Keith Ryden, Rémi Pacaud, Thierry Paulmier, Pierre Sarrailh, Denis Payan, David Rodgers (2019)Validation of Internal Charging Tools with Experiments in REEF, In: IEEE Transactions on Plasma Science Institute of Electrical and Electronics Engineers (IEEE)
B Taylor, CI Underwood, KA Ryden, PA Morris (2009)A GIOVE derived galileo electron spectrum and comparison to models, In: IEEE Transactions on Nuclear Science56(6)pp. 3423-3428
C Dyer, Alexander Hands, Keith Ryden, F Lei (2017)Extreme Atmospheric Radiation Environments & Single Event Effects, In: IEEE Transactions on Nuclear Science65(1)pp. 432-438 IEEE

Data from ground-level radiation monitors and cosmogenic nuclides are combined to a give a probability distribution for severe radiation events related to the well quantified event of 23 February 1956. Particle fluxes, single event effects rates and dose rates are calculated for ground-level and aerospace systems. The event of February 1956 would provide a challenge to air safety while more extreme events seen in historical records would challenge safety-critical ground systems. A new space weather hazard scale based on this event could be used to give rapid assessment of the radiation hazard using high latitude neutron monitor data.

D Rodgers, H Evans, C Underwood, B Taylor, K Ryden, G Mandorlo, E Daly (2008)Lessons learned on Galileo radiation environment from GIOVE, In: International Astronautical Federation - 59th International Astronautical Congress 2008, IAC 200813pp. 8277-8281
KA Ryden, PA Morris, DJ Rodgers, CS Dyer, CI Underwood, B Taylor, S Jason, HD Evans, EJ Daley, G Mandorlo, G Gatti (2006)Initial radiation measurements from Europe's Galileo test-bed satellite, GIOVE-A, In: AIAA 57th International Astronautical Congress, IAC 20064pp. 2775-2782

In preparation for deployment of the Galileo satellite navigation system, Europe has launched a test satellite, Giove-A. One of its objectives is to measure the radiation environment encountered in medium Earth orbit (MEO) which is a new regime for European missions. Giove-A therefore includes two radiation environment monitors: Merlin supplied by QinetiQ and CEDEX supplied by the University of Surrey. Merlin measures electrostatic charging and electron fluxes, total ionising dose, energetic proton fluxes and heavy ion linear energy transfer (LET) spectra. CEDEX monitors energetic proton fluxes, heavy ion linear energy transfer (LET) spectra and ionising dose rates. Giove-A, which was built by SSTL (UK), was successfully launched on 28th December 2005 into a 23,600 km circular, 56 degree inclination orbit. Data received since launch has been analysed and demonstrates that the MEO environment is highly dynamic due to the influence of space weather. Numerous electron belt enhancement events have been observed and the charging effects of these events been characterised. Total ionising dose is also seen to be delivered almost wholly during electron events.

KA Ryden, PA Morris, KA Ford, CS Dyer, A Hands, B Taylor, CI Underwood, DJ Rodgers, G Mandorlo, G Gatti, HD Evans, EJ Daly (2007)Observations of internal charging and outer-belt electron enhancements from Giove-A, In: Proceedings of the European Conference on Radiation and its Effects on Components and Systems, RADECS

The planned Galileo global navigation system will employ an array of satellites in medium Earth orbit. Internal charging is one of the primary hazards for any spacecraft in MEO and accordingly the Galileo test spacecraft, Giove-A, carries the 'SURF' detector to undertake measurements of internal charging currents deposited at three different shielding depths (0.5, 1.0 and 1.5 mm AI). Giove-A was successfully launched on 28th December 2005 into a 23,300 km circular, 56 degree inclination orbit. In this paper we provide data on the charging currents observed in 2006, with particular emphasis on two large charging events, one in April and one in December. Comparisons are made between the flight data and predictions made using ESA's internal charging tool, DICTAT, which employs the FLUMIC 'worst case' electron belt model. The DICTAT predictions of charging current are exceeded for a few days in the 1.5mm AI shielded plate in the course of the December event. © 2007 IEEE. © 2007 IEEE.

Alexander Dyer, Keith Ryden, Alexander Hands, Clive Dyer, C. Burnett, M. Gibbs (2018)Zenith: A Radiosonde detector for Rapid-Response Ionising Atmospheric Radiation Measurements during Solar Particle Events, In: Space Weather16(3)pp. 261-272 American Geophysical Union

Solar energetic particle events create radiation risks for aircraft, notably single event effects (SEEs) in microelectronics along with increased dose to crew and passengers. In response to this, some airlines modify their flight routes after automatic alerts are issued. At present these alerts are based on proton flux measurements from instruments on-board satellites, so it is important that contemporary atmospheric radiation measurements are made and compared. This paper presents the development of a rapid-response system built around the use of radiosondes equipped with a radiation detector, Zenith, which can be launched from a Met Office weather station after significant solar proton level alerts are issued. Zenith is a compact, battery-powered solid-state radiation monitor designed to be connected to a Vaisala RS-92 radiosonde which transmits all data to a ground station as it ascends to an altitude of ~33 km. Zenith can also be operated as a stand-alone detector when connected to a laptop, providing real-time count rates. It can also be adapted for use on unmanned aerial vehicles. Zenith has been flown on the Met Office Civil Contingency Aircraft (MOCCA), taken to the CERN-EU high energy Reference Field (CERF) facility for calibration and launched on a meteorological balloon at the Met Office's weather station in Camborne, Cornwall, UK. During this sounding, Zenith measured the Pfotzer-Regener maximum to be at an altitude of 18 - 20 km where the count rate was measured to be 1.15 counts s-1 cm-2 compared to 0.02 counts s-1 cm-2 at ground level.

Alexander Hands, Keith Ryden, Remi Pacaud, Thierry Paulmier, Pierre Sarrailh, Denis Payan, David Rodgers (2019)Validation of Internal Charging Tools With Experiments in REEF, In: IEEE Transactions on Plasma Science47(8)pp. 3824-3833 Institute of Electrical and Electronics Engineers (IEEE)

The objective of the European Space Agency validation of internal charging tools using the realistic electron environmental facility (REEF) project is to assess the performance of internal charging tools against experimental measurements made at the REEF facility at the University of Surrey. REEF uses an intense strontium-90 beta-emitting radioactive source to simulate the space environment. This project is complemented by parallel experiments to derive material parameters, conducted by ONERA. We report results from REEF with four different types of dielectric material and compare these results to predictions from the DICTAT, MCICT, and NUMIT internal charging simulation tools. The materials under investigation are Cirlex, PEEK, FR4, and Neoflon (FEP). We find that in many cases, the computer codes struggle to recreate REEF results, which raises significant questions over the validity of internal charging mitigation analyses. We show the advantages and disadvantages of each model and suggest what features could be added in order to improve the fidelity of their predictions.

Alexander Hands, Keith Ryden (2017)Experimental Measurement of Low-Intensity and Long-Duration Internal Charging Behavior, In: IEEE Transactions on Plasma Science45(8)pp. 1938-1946 IEEE

We report initial results from the EU FP7 Spaces- torm project on the experimental behavior of commonly-used space dielectric materials in an electron environment where the incident electron current is significantly below safe levels specified by design standards. The realistic electron environment facility (REEF), which uses an intense strontium-90 beta-emitting radioactive source to simulate the space environment, has been recommissioned at the University of Surrey for this purpose. Using a combination of shielding and variable source-sample separation REEF can achieve a very wide dynamic range in electron current, from the very high levels associated with an extreme space weather event, down to the levels below the Euro13 pean Cooperation for Space Standardization low temperature (

Keith Ryden, PA Morris, KA Ford, ADP Hands, CS Dyer, B Taylor, Craig Underwood, DJ Rodgers, G Mandorlo, G Gatti, HDR Evans, EJ Daly (2008)Observations of Internal Charging Currents in Medium Earth Orbit, In: IEEE TRANSACTIONS ON PLASMA SCIENCE36(5)pp. 2473-2481 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Alexander Hands, Keith Ryden, CJ Mertens (2016)The Disappearance of the Pfotzer-Regener Maximum in Dose Equivalent Measurements in the Stratosphere, In: Space Weather14(10)pp. 776-785 American Geophysical Union

The NASA Radiation Dosimetry Experiment (RaD-X) successfully deployed four radiation detectors on a high altitude balloon for a period of approximately twenty hours. One of these detectors was the RaySure in-flight monitor, which is a solid-state instrument designed to measure ionizing dose rates to air crew and passengers. Data from RaySure on RaD-X show absorbed dose rates rising steadily as a function of altitude up to a peak at approximately 60,000 feet, known as the Pfotzer-Regener maximum. Above this altitude absorbed dose rates level off before showing a small decline as the RaD-X balloon approaches its maximum altitude of around 125,000 feet. The picture for biological dose equivalent, however, is very different. At high altitudes the fraction of dose from highly ionizing particles increases significantly. Dose from these particles causes a disproportionate amount of biological damage compared to dose from more lightly ionizing particles and this is reflected in the quality factors used to calculate the dose equivalent quantity. By calculating dose equivalent from RaySure data, using coefficients derived from previous calibrations, we show that there is no peak in the dose equivalent rate at the Pfotzer-Regener maximum. Instead the dose equivalent rate keeps increasing with altitude as the influence of dose from primary cosmic rays becomes increasingly important. This result has implications for high altitude aviation, space tourism and, due to its thinner atmosphere, the surface radiation environment on Mars

A Hands, K Ryden, C Underwood, D Rodgers, H Evans (2015)A New Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC), In: IEEE TRANSACTIONS ON NUCLEAR SCIENCE62(6)pp. 2767-2775 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
B Taylor, C Underwood, HDR Evans, E Daly, KA Ryden, G Santin (2008)Galileo GIOVE-A MEORAD Results and Analysis, In: IEEE T NUCL SCI55(6)pp. 3151-3157 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The Giove-A spacecraft carries two radiation monitors, CEDEX, built by the University of Surrey and Merlin, built by QinetiQ, to study the radiation environment encountered in the Galileo orbit. The two monitors have been functioning since the beginning of the mission and have measured protons, heavy ions and electrons. The electron environment has been found to be highly variable and driven by solar interactions. Comparisons with AE-8 indicate that the electron energy spectrum for the period measured was somewhat harder than that expected from the model. A series of large Solar proton events were detected in December 2006, registering as enhanced fluxes of protons, heavy ions and also triggering a large enhancement in the outer electron belt. Comparisons with POLE and INTEGRAL/IREM show an improved spectral match over AE-8.

C Dyer, A Hands, F Lei, P Truscott, KA Ryden, P Morris, I Getley, L Bennett, B Bennett, B Lewis (2009)Advances in measuring and modeling the atmospheric radiation environment, In: IEEE Transactions on Nuclear Science56(6)pp. 3415-3422

New radiation monitors based on solid-state detectors have been developed to perform wide-ranging measurements of the atmospheric environment and provide warnings of sudden increases during solar particle events. Results have been obtained during the current deep solar minimum across the full range of latitudes and from sea level to 13 km altitude. Results for ambient dose equivalent agree very closely with Tissue Equivalent Proportional Counters carried on the same flights. Values of 10 μSv/hr are being reached at 12 km altitude and high latitude. Comparisons are made with the QinetiQ Atmospheric Radiation Model and the need to include cosmic-ray heavy ions is demonstrated. © 2009 IEEE.

D Lazaro, S Bourdarie, Alexander Hands, Keith Ryden, P Nieminen (2010)Electron environment specification models for Galileo, In: 38th COSPAR Scientific Assembly Proceedings
Paul Cannon, Matthew Angling, Les Barclay, Charles Curry, Clive Dyer, Robert Edwards, Graham Greene, Michael Hapgood, Richard Horne, David Jackson, Cathryn Mitchell, John Owen, Andrew Richards, Christopher Rogers, Keith Ryden, Simon Saunders, Martin Sweeting, Rick Tanner, Alan Thomson, Craig Underwood (2013)Extreme space weather: impacts on engineered systems and infrastructure Royal Academy of Engineering
Bryn Jones, C Dyer, Alexander Hands, R Iles, Keith Ryden, M Smith, M Stills, G Taylor (2010)Development in Aviation Space Weather Services, In: AMS Poster paper

In 1998, the first Polar route test flight between Asia and North America was carried out. By the end of 2009, over 10,000 Polar flights will have taken place. However, as cross polar traffic continues to increase, the aviation industry is realising the impacts that space weather has on high-altitude, high-latitude, flights (>50N) and polar operations (>78N). Effects include disruption in High Frequency (HF) communications, satellite navigation system errors, and radiation hazards to humans and avionics. These concerns not only apply to current operations, but become even more important at all latitudes when considered within the framework for the Next Generation Air Transportation System (NextGen), an interagency initiative to transform the U.S. air transportation system by 2025. The AMS/SolarMetrics report, Integrating Space Weather Observations and Forecasts into Aviation Operations (published March 2007), offers recommendations to increase the safety, reliability, and efficiency of aviation operations through more effective use of space weather information. This report highlighted several policy issues that need to be addressed to ensure the best use of current and future space weather information, namely: . Communication of space weather information . Standardization of information and regulations . Education and training . Cost benefit and risk analysis SolarMetrics is working with the airline and space transportation industries to identify and develop new integrated space weather services that will meet their demands for real-time operational decision tools and products. This poster will present some of the operational issues raised above and how they are being tackled.

KA Ryden, PA Morris, Alexander Hands, V Alpe (2010)Measurements of internal charging currents in MEO: 2005-2010, In: 11th Spacecraft Charging Technology Conference Proceedings
Alexander Dyer, Alex Hands, Keith Ryden, Clive Dyer, Ian Flintoft, Alexis Ruffenach (2020)Single-Event Effects in Ground-Level Infrastructure During Extreme Ground-Level Enhancements, In: IEEE Transactions on Nuclear Science67(6)pp. 1139-1143 Institute of Electrical and Electronics Engineers

We take an initial look at hard single-event effects (SEEs) in power electronics and static random access memories (SRAMs) during space weather-induced extreme ground-level enhancement (GLE) events. We show that there is a significant risk of failure of silicon power metal–oxide–semiconductor field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) at ground level during a 10× February ’56 GLE. If the devices are not derated, then we find that 21% of power MOSFETs and 14% of IGBTs are, in the worst case, predicted to fail. The probability of failure increases to 68% and 52% during a once-in-a-10 000-year GLE for power MOSFETs and IGBTs, respectively. Silicon carbide devices show a lower failure rate by more than an order of magnitude, where only 2.8% are predicted to fail during a once-in-a-10 000-year GLE. It is clear that these events could disrupt critical infrastructure if mitigating precautions are not implemented.

B Taylor, Craig Underwood, HDR Evans, Keith Ryden, D Rodgers, EJ Daly, G Mandorlo, M Falcone, PA Morris, RG Prieto (2007)Results from the Galileo giove - A radiation monitors and comparison with existing radiation belt models, In: IEEE TRANSACTIONS ON NUCLEAR SCIENCE54(4)pp. 1076-1081 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The radiation monitors on board the Galileo Giove-A satellite, CEDEX and Merlin, and their data are presented. The instruments include energetic proton and ion detectors, an internal charging monitor, RADFETs and experimental dose-rate photodiodes. A comparison of the data with existing monitors and models is presented.