Electromagnetics & Space Environment Division – TEC-EES Electromagnetics & Space Environment Division – TEC-EES Observations of the GALILEO radiation environment

Electromagnetics & Space Environment Division – TEC-EESElectromagnetics & Space Environment Division – TEC-EES

Observations of the GALILEO radiation environment from MERLIN and SREM

instrumentsDavid 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


GALILEOGalileo – 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.

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)


GIOVEGiove-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-A

Giove-B


MERLIN•Developed by QinetiQ•Evolution of the SURF and CREDO instruments•Mass – 1kg (2kg including CAN bus and additional shielding)

•Launched on Giove-A 28th Dec 2005.

Electron monitor•3x70mm ø aluminium plates•2 sensitivity ranges

RadFETS•3mm Al and 6mm Al shielding•Unbiased


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: 40-100MeVLET: 16 channels100 – 20000 MeV/g/cm2


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


Giove-B SREM

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

06/05/08 19:12 07/05/08 00:00 07/05/08 04:48 07/05/08 09:36 07/05/08 14:24 07/05/08 19:12 08/05/08 00:00

Coun

trate

(#/s

)TC1 (#/s)

TC2 (#/s)

TC3 (#/s)06

/05/

08 2

1:59

07/0

5/08

20:

56

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


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


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

2007


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


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

1/8/06 – 1/1/07


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


Cumulative charge – AE8MAX and MERLIN






Plate 1 (>0.8MeV)

Plate 3 (>1.6MeV)

FLUMIC v2 comparison


ConclusionsA 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.


ConclusionsFLUMIC2 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


END


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.


CEDEX and MERLIN for the first 5 months of 2006.


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


1.E+04

1.E+05

1.E+06

1.E+07

1 2 3 4 5 6 7 8 9L-shell

Flu

x cm

-2 s

-1

AE-8 MINGalileoGPSGEO

>1MeV electron flux according to AE-8.



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

GPS Electron Spectra

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0.1 1 10Energy [MeV]

Flu

x [/

cm2/

s/sr

]

MEOv2 lower

MEOv2 mean

MEO v2 upper

AE-8 (7 years MAX, 4 years MIN)


Data ProcessingMerlin data processed by SSTL/UoS in collaboration with QinetiQ

Data products provided to the Galileo Project

PSI access SREM data

Documents

Electromagnetics & Space Environment Division – TEC-EES Electromagnetics & Space Environment Division – TEC-EES Observations of the GALILEO radiation environment