Flight results from the Merlin space weather monitor on Giove-A

1. Flight results from the Merlin space weather monitor on Giove-A 3rd European Space Weather Week 13-17 November 2006, Brussels K A Ryden, P A Morris, D J Rodgers, C S Dyer - QinetiQ C I Underwood, B. Taylor, S Jason - SSTL/ University of Surrey H D Evans, E J Daly, G Mandorlo, G Gatti - ESA/ESTEC

2. Giove-A • Test-bed for European Galileo GNSS • obtain frequency filing protection • characterise the MEO environment • validate certain critical payloads • provide representative signal-in-space transmission • Built and operated by SSTL • Successfully launched in December 2005 • Orbit 23,260 km and 56 degrees inclination, 27 month lifetime • electron dominated: charging and total dose hazards • exposed to solar particle events SSTL image

3. Galileo orbit • Severe trapped electron environment • Charging effects • Total ionising dose • Galactic cosmic rays • Solar protons and ions

4. Total ionising dose

5. Internal charging High energy electrons from space environment • ESD transients can cause anomalies and outages • Cables, connectors, pcbs etc Shielding Dielectric

6. Merlin space weather hazard monitor • Electrons and charging • Total ionising dose • Protons • Ions (LET) • 1kg, 2.5W (standard) Developed from the earlier CREDO and SURF science detectors

7. QinetiQ space radiation monitors • CREAM Cosmic Ray Effects and Activation Monitor (1986 onward) • Charge deposition events in Si • Flights: Shuttle(10 flights) /BA Concorde/Qantas/ • CREDO Cosmic Ray Effects and Dosimetry Experiment (1991 onward) • Ion LET spectra and proton flux • Flights: UoSAT, STRV1a, Skynet, APEX, MIR, MPTB • SURF (2000 onward) • Surface charging and internal charging (electron flux) • Flights: STRV1d • Merlin (2005 onward) • Charging/LET spectra/proton flux/TiD • Flights: Giove-A, LWS/SET

8. Merlin space weather hazard monitor Electrons & electrostatic charging (3 shielding depths) Total dose RADFET (x2) Protons (>40 MeV flux) Ions (linear energy transfer) Integral rad-hard computer, data storage, power conditioning and communications

9. Merlin block diagram Sensor suite (CREDO + SURF + Radfet) Data handling

10. Merlin-Giove-A

11. Space radiation Lid 0.6mm Al particles 0.5mm Al plate 1.0mm Al plate Satellite exterior wall fA fA Satellite ground Satellite reference telemetry system . Electrons & charging: SURF experiment • Novel approach • internal charging current vs depth measurement • each plate has unique energy response curve so spectrum can be obtained • Virtually immune to proton contamination • Built and flown on STRV1d • 300g, 0.3W

12. SURF experiment: internal charging mode

13. SURF results • GTO orbit • 500 x 36,000 km

14. Merlin-Giove-A • Located externally (under thermal blanket) • Extra box shielding incorporated (5mm thick walls) due to severity of orbit • SURF and Radfet set-up for Giove-A: 2 mm Al Thermal blanket - 0.1 mm Al eq. 0.4 mm Al Housing (lid) 5 mm Al SURF plates 0.5 mm Al 1 mm Al RADFETS

15. Merlin pre-flight calibration REEF Sr-90 source

16. Realistic Electron Environment Facility • 90Sr  source: 3.7 G Bq • Vacuum chamber • -10 to +40°C temperature control of thermal plate • Electron current controlled by variation of source-to -sample distance • ESD detection system • Surface potential measurements (‘TREK’ probes)

17. Electron spectrum comparisons • REEF capability brackets the average (AE8) and worst-case (FLUMIC) electron environments predicted for GEO

18. Merlin pre-flight calibration in REEF

19. Merlin-Giove-A • Two particle telescopes (CREDO) • ion LET spectrum • protons (400 keV energy deposition threshold) COINCIDENCE COUNTERS Si diode, area 3cm2, 300um thick NON-COINCIDENCE COUNTERS Pulse height discriminator COINCIDENCE GATE SIGNAL

20. Radiation monitors installed on Giove-A Picture: SSTL

21. Launch 28th December 2005

22. 1st day of data: electrons/charging

23. Jan & Feb 2006: electrons/charging

24. Jan & Feb 2006: electrons & dose

25. 21 Feb 2006 electron event

26. 6 days later

27. Jan-May 2006: electrons & dose

28. April 06 electron event

29. April 06 electron event

30. Single belt transit – 17th April 2006

31. Jan-Aug 2006: electrons and dose

32. Jan-Aug 2006: electrons and dose AE8/sectored shielding model of the expected dose.

33. Sept & Oct 2006: electrons and dose

34. Jan-Oct 2006: electrons and dose (Daily average)

35. Jan-Aug 2006: electrons and FLUMIC seasonal modulation function

36. Jan-Oct 2006: top SURF plate compared to DICTAT worst case

37. Jan-Oct 2006: middle SURF plate compared to DICTAT worst case

38. Jan-Oct 2006: bottom SURF plate compared to DICTAT worst case

39. Jan-Aug 2006: electron spectrum ‘hardness’

40. 6th July 2006 – minor SPE

41. Background LET spectrum

42. Conclusions • Good data from all Merlin sensors • Electrons/charging rates measured at three shielding depths • Total dose at two shielding depths • > 40 MeV protons (500 keV deposition threshold to be sure of protons) • LET spectrum (background) • Numerous electron enhancement events have been observed via the charging (electron deposition) and total dose effects • Clear 27 day interval in electron enhancements (persistent coronal holes) • April ‘event’ was the most severe so far • ‘worst case’ events are of engineering significance and their magnitude needs to be captured • April event still produced less than DICTAT ‘worst case’ predicted charging currents for the plates

43. …..conclusions • Ionising dose is delivered in surges during the electron events • From Jan to August 2006, approximately half of the dose was delivered by just one electron event • Dose at 6mm shield depth (Merlin +z direction) observed is greater than the predicted value (using AE8/sectored shielding models) at this stage: however may not be typical of whole solar cycle • Post-script • 2nd Merlin for NASA ‘Living with a Star’ now built & qualified