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Observations of the GALILEO radiation environment from MERLIN and SREM instruments

Observations of the GALILEO radiation environment from MERLIN and SREM instruments. David Rodgers, Hugh Evans , Eamonn Daly, Ali Mohammadzadeh, ESA/ESTEC, Noordwijk, The Netherlands Keith Ryden, Alex Hands, Clive Dyer QinetiQ Ltd, Farnborough, Hampshire, UK Craig Underwood, Ben Taylor

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Observations of the GALILEO radiation environment from MERLIN and SREM instruments

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  1. Observations of the GALILEO radiation environment from MERLIN and SREM instruments David Rodgers, Hugh Evans, Eamonn Daly, Ali Mohammadzadeh, ESA/ESTEC, Noordwijk, The Netherlands Keith Ryden, Alex Hands, Clive Dyer QinetiQ Ltd, Farnborough, Hampshire, UK Craig Underwood,Ben Taylor University of Surrey, Guildford, UK

  2. Galileo – Europe’s future Global Navigation Satellite System 23200km altitude circular orbit 3 orbital planes at 56° inclination. 9 equally-spaced operational satellites per plane, plus 1 spare. GALILEO • Radiation Environment • Main threat comes from relativistic electrons • Electrons are trapped in two belts around the Earth. • Galileo orbit lies at and above the outer belt peak. (higher than GPS)

  3. Giove-A and -B Secure the frequencies allocated by the International Telecommunications Union (ITU) Verify critical technologies e.g. atomic clocks and signal generator Provide a test signal for ground-based systems. Characterise the radiation environment of the Galileo orbit. GIOVE Giove-A Giove-B

  4. MERLIN • Developed by QinetiQ • Evolution of the SURF and CREDO instruments • Mass – 1kg (2kg including CAN bus and additional shielding) • Launched on Giove-A28th Dec 2005. • Electron monitor • 3x70mm ø aluminium plates • 2 sensitivity ranges • RadFETS • 3mm Al and 6mm Al shielding • Unbiased

  5. MERLIN • Two telescopes • Heavy Ion LET • Proton Flux • Each Telescope • - Two large-area planar silicon diodes • Species discrimination through pulse-height analysis • Non-coincidence channels • Coincident channels • Protons: 40-100MeV • LET: 16 channels • 100 – 20000 MeV/g/cm2

  6. SREM • Developed by Oerlikon/Contraves and PSI (Switzerland) • Evolution of REM • One of a set of near-identical instruments purchased by ESA. • Mass 2.5kg • Power <2W • Launched on Giove-B on 26th April 2008 • Previously launched on Integral, STRV-1C, Proba-1 and Rosetta • 3 x Si surface barrier detectors • >0.5MeV electrons • >10MeV protons • >150MeV ions

  7. Giove-B SREM count-rate for 1 day (~ >0.8, >2.0 >2.8MeV)

  8. Solar wind velocity SREM (>0.8 MeV, >2 MeV and >2.8 MeV) MERLIN (>0.8MeV, >1.0MeV and >1.6MeV) 13-17 June 2008

  9. 2007 MERLIN currents [>0.8 (white), >1.0 (dark green) and >1.6MeV (red)] and doses [3mm (light green) and 6mm (pink) Al equivalent].

  10. >40MeV protons, >1.6MeV electrons and dose under 6mm Al

  11. 1/8/06 – 1/1/07 >0.8MeV electrons and “hardness index” plate1/plate3

  12. SREM electron data (>2MeV) from GIOVE-B (red) and INTEGRAL (green)

  13. Cumulative charge – AE8MAX and MERLIN

  14. Cumulative charge – AE8MAX and MERLIN

  15. Cumulative charge – AE8MAX and MERLIN

  16. Plate 1 (>0.8MeV) Plate 3 (>1.6MeV) FLUMIC v2 comparison

  17. A new radiation environment is being explored. Merlin and SREM are returning good-quality data. There is good agreement between the datasets. Spacecraft in the Galileo orbit are subject to frequent space weather enhancements of the outer belt in response to changes in the solar wind. Electron enhancements are the dominant source of dose. Hardening of electron spectra during enhancements is typically seen. These instruments can tell us about space weather and the long term environment. Conclusions

  18. FLUMIC2 model may be too conservative for >0.8MeV electrons exceeded by CME-related enhancement consider yearly maximum for FLUMIC, for this orbit AE-8 model conservative ~0.8 MeV under-predicts at higher energy Divergence from the AE-8 model is within model uncertainties (factor 2-3) A small fraction of one solar has been monitored. Further monitoring with IOV/FOC are planned EMU - a Merlin-like instrument Conclusions

  19. END

  20. The GIOVE satellites (A, B) are test satellites for the European Galileo constellation. It is recognized that the Galileo orbital radiation environment is particularly severe and therefore these satellites carry environment monitoring equipment. This contribution will present some of the observations made and discuss what they teach us about the environment expected for the final Galileo constellation. Abstract

  21. CEDEX and MERLIN for the first 5 months of 2006.

  22. MERLIN currents [>0.8 (red), >1.0 (blue) and >1.6MeV (black)] and doses [3mm (orange) and 6mm (yellow) Al equivalent].

  23. >1MeV electron flux according to AE-8.

  24. ONERA MEOv2 and AE-8 model spectra for the GPS orbit.

  25. Merlin data processed by SSTL/UoS in collaboration with QinetiQ Data products provided to the Galileo Project PSI access SREM data Data Processing

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