Flight results from the Merlin space weather monitor on Giove-A 3 rd European Space Weather Week 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

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

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

Total ionising dose

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

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

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

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

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

Merlin-Giove-A

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 Space radiation particles Satellite telemetry system Lid 0.6mm Al 0.5mm Al plate 1.0mm Al plate Satellite exterior wal l Satellite ground reference fA.

SURF experiment: internal charging mode

SURF results GTO orbit 500 x 36,000 km

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: SURF plates Housing (lid) RADFETS 0.4 mm Al 2 mm Al 5 mm Al 0.5 mm Al 1 mm Al Thermal blanket mm Al eq.

Merlin pre-flight calibration REEF Sr-90 source

Realistic Electron Environment Facility 90 Sr  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)

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

Merlin pre-flight calibration in REEF

Two particle telescopes (CREDO) – ion LET spectrum – protons (400 keV energy deposition threshold) Pulse height discriminator COINCIDENCE GATE SIGNAL Si diode, area 3cm 2, 300um thick NON-COINCIDENCE COUNTERS COINCIDENCE COUNTERS Merlin-Giove-A

Radiation monitors installed on Giove-A Picture: SSTL

Launch 28 th December 2005

1 st day of data: electrons/charging

Jan & Feb 2006: electrons/charging

Jan & Feb 2006: electrons & dose

21 Feb 2006 electron event

6 days later

Jan-May 2006: electrons & dose

April 06 electron event

Single belt transit – 17 th April 2006

Jan-Aug 2006: electrons and dose

AE8/sectored shielding model of the expected dose.

Sept & Oct 2006: electrons and dose

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

Jan-Aug 2006: electrons and FLUMIC seasonal modulation function

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

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

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

Jan-Aug 2006: electron spectrum ‘hardness’

6th July 2006 – minor SPE

Background LET spectrum

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

…..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 –2 nd Merlin for NASA ‘Living with a Star’ now built & qualified