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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

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

galileo
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)
giove
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

merlin
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
merlin1
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
slide6
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
slide8

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

slide9

2007

MERLIN currents [>0.8 (white), >1.0 (dark green) and >1.6MeV (red)]

and doses [3mm (light green) and 6mm (pink) Al equivalent].

slide11

1/8/06 – 1/1/07

>0.8MeV electrons and “hardness index” plate1/plate3

slide16

Plate 1 (>0.8MeV)

Plate 3 (>1.6MeV)

FLUMIC v2 comparison

conclusions
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
conclusions1
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
abstract
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
slide22

MERLIN currents [>0.8 (red), >1.0 (blue) and >1.6MeV (black)]

and doses [3mm (orange) and 6mm (yellow) Al equivalent].

data processing
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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