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© Copyright QinetiQ limited 2006 A New Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC) Alex Hands 1, Keith Ryden 1, Craig Underwood.

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Presentation on theme: "© Copyright QinetiQ limited 2006 A New Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC) Alex Hands 1, Keith Ryden 1, Craig Underwood."— Presentation transcript:

1 © Copyright QinetiQ limited 2006 A New Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC) Alex Hands 1, Keith Ryden 1, Craig Underwood 1, David Rodgers 2 and Hugh Evans 2 1 University of Surrey, Guildford, United Kingdom 2 European Space Agency, ESTEC, Netherlands 15 th July 2015, NSREC, Boston

2 www.QinetiQ.com © Copyright QinetiQ limited 2006 2 15 th July 2015, NSREC, Boston Outline Background Internal Charging Existing Models The SURF Instrument Electron flux determination The MOBE-DIC Model Input Data Worst-Case Estimation Outer Belt Extrapolation Implementation

3 www.QinetiQ.com © Copyright QinetiQ limited 2006 3 15 th July 2015, NSREC, Boston Internal Charging Energetic trapped electrons in Van Allen belts pose a threat to satellites through internal charging of dielectric materials: The outer electron belt is extremely dynamic - large changes in flux occur over short timescales, driven by coronal holes and coronal mass ejections (CMEs) Radiation belt pumping e.g. April 2010: >2 MeV flux at GEO increases by ~4 orders of magnitude in a few hours! Electrostatic charging of spacecraft materials Electrostatic discharge Energy coupling into circuit Satellite anomaly / outage /failure

4 www.QinetiQ.com © Copyright QinetiQ limited 2006 4 15 th July 2015, NSREC, Boston Existing Environment Models Several models describe the Van Allen belts: AE8: Industry standard for decades Static model – no flux variability Inadequate for internal charging AE9: Successor to AE9 Multiple data sources Comprehensive statistics Complex (many input parameters & run options) FLUMIC: Worst-case model for internal charging Based primarily on GEO data (not near peak) User-friendly but not up-to-date Various others targeted at specific environments/orbits Objective of this work: develop new simple model for internal charging worst case environment - successor to FLUMIC but based on medium Earth orbit (MEO) data Vette (1991) Johnston et al. (2014)

5 www.QinetiQ.com © Copyright QinetiQ limited 2006 5 15 th July 2015, NSREC, Boston The SURF Detector Part of Merlin instrument suite on Giove-A (technology demonstrator for Galileo) Medium Earth Orbit (~23,200 km, 56°) SURF Three stacked aluminium charge-collecting plates Direct measure of energetic electrons No proton contamination or dead-time Launched in 2005

6 www.QinetiQ.com © Copyright QinetiQ limited 2006 6 15 th July 2015, NSREC, Boston SURF Data Giove-A / Galileo orbit is in the heart of the outer belt Perfect location for internal charging currents First Day: First 6 months: Recurrence of coronal hole Samples peak of belt every ~7 hours

7 www.QinetiQ.com © Copyright QinetiQ limited 2006 7 15 th July 2015, NSREC, Boston SURF Data 2005 – 2014:

8 www.QinetiQ.com © Copyright QinetiQ limited 2006 8 15 th July 2015, NSREC, Boston Electron Flux Determination Instrument response functions determined by Monte Carlo simulations: Iterative fit used to derive flux based on assumed exponential spectrum Validated with independent fluxes from other Giove instruments (SREM, Cedex) Need flux, rather than current to produce model…

9 www.QinetiQ.com © Copyright QinetiQ limited 2006 9 15 th July 2015, NSREC, Boston Worst Case Statistics Use derived flux time series to create cumulative distribution functions (CDFs) at discrete energies in the range 0.5 – 3 MeV (peak of instrument response) (Note: harder spectra in more extreme events) Fit baseline spectra at three confidence levels - 90%, 99% & 100%: Create reduced series of average flux at equatorial peaks (L≈4.7) CDFs based on equatorial flux: These three spectra form the basis of the MOBE-DIC model

10 www.QinetiQ.com © Copyright QinetiQ limited 2006 10 15 th July 2015, NSREC, Boston Extrapolating to other L-Shells Equatorial spectra at L≈4.7 form the basis of the model Need to derive profile of L-shell to extrapolate, however… L-Shell profile is not stable, e.g.: SURF on STRV1d (Ryden et al. 2001) Van Allen Probes, REPT (Baker et al. 2014) AE8 AE9 FLUMIC Van Allen Probes, ERM (Maurer et al. 2013)

11 www.QinetiQ.com © Copyright QinetiQ limited 2006 11 15 th July 2015, NSREC, Boston Extrapolating to other L-Shells (2) Our approach is to use high-latitude SURF data Inclination of Giove-A orbit means higher L shells only encountered at higher latitudes Need to renormalise non-equatorial fluxes: L≈4.7 at equator Assume Vette function (like AE8 and FLUMIC) [Scaling is (slightly) L-dependent but not energy-dependent] Equatorial Flux All Flux Fit ‘envelope’ to renormalised data (at each energy) ￫ Energy-dependent L-Shell profile

12 www.QinetiQ.com © Copyright QinetiQ limited 2006 12 15 th July 2015, NSREC, Boston Extrapolating to other L-Shells (3) Final (energy-dependent) L-shell profile (3 < L < 8) FLUMIC function used below L=4.5 (no Giove data) Normalised to L=4.7: Normalised to L=6.6: (NB slightly modified version used for integral flux)

13 www.QinetiQ.com © Copyright QinetiQ limited 2006 13 15 th July 2015, NSREC, Boston Comparison to GOES data Equivalent CDFs constructed from GOES (geostationary) electron flux data Compare with MOBE-DIC prediction at L=6.6: >2 MeV flux adjusted to L=6.6 and for dead-time effects (Meredith et al., 2015) MOBE-DIC prediction for ‘100%’ (worst case) at GEO for >2 MeV flux is: 2.34 x 10 5 e/cm 2 /s/sr Theoretical upper limit (Koons et al. 2001)… 2.34 x 10 5 e/cm 2 /s/sr !! Good agreement between MOBE- DIC and GOES at 99% and 100% (slightly worse at 90% due to conservative L-shell envelope) Unsurprisingly, excellent consistency at L=4.7 (MEO)

14 www.QinetiQ.com © Copyright QinetiQ limited 2006 14 15 th July 2015, NSREC, Boston Comparison to existing models Comparison to FLUMIC model (other comparisons in paper): Differential Spectra Integral Spectra MOBE-DIC gives harder spectrum at MEO Good agreement at GEO (FLUMIC in between 99% & 100% MOBE-DIC level)

15 www.QinetiQ.com © Copyright QinetiQ limited 2006 15 15 th July 2015, NSREC, Boston MOBE-DIC: Implementation MOBE-DIC model is defined by a set of parameters and simple equations At present simple spreadsheet implementation: Public version available on request (a.hands@surrey.ac.uk) To be made available via Spenvis…

16 www.QinetiQ.com © Copyright QinetiQ limited 2006 16 15 th July 2015, NSREC, Boston Summary Data from Giove (A & B) satellites analysed and cross-correlated Spacecraft now graveyarded, SREM and Cedex instruments ceased in 2012 Merlin instrument (including charging current, proton telescope and RadFETs) continues to collect useful data on Giove-A SURF charging currents used to calculate electron flux (free from proton contamination) ‘Worst case’ fluxes derived as function of confidence level at MEO Non-equatorial fluxes used to extrapolate to other L-shells Implemented in new Model of Outer Belt Electrons for Dielectric Internal Charging (MOBE-DIC) (successor to FLUMIC) Aimed at spacecraft engineering community, specifically for concerns over internal charging during enhanced environments To be made publically available via Spenvis

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