Estimating the risk of SEPE: a service dedicated to spacecraft operations - Feedback from ATV missions Ph. Yaya, L. Hecker CLS (Collecte Localisation Satellites) Toulouse, FRANCE

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Effect of particles on space vehicles Charged particles are well known to be hazardous for on-board electronics. Miniaturization and digitization of electronics and logic circuits have made space vehicles (launchers/satellites/…) more vulnerable to radiation. Origin of radiation : Van Allen radiation belts (mostly trapped p+/e-)  SAA Cosmic rays (very high energies but very low flux) Proton solar flares  « feed » radiation belts + direct impact if intense enough

Effect of particles on space vehicles Mean rate of daily SEU on all memories for SAC-C satellite (alt. 715 km) (from C. Boatella-Polo, CNES) Position of UOSAT-3 (alt. 785 km) when memory errors were detected (Fabien Faure, PhD thesis, INPG, 2005)

Effect of particles on space vehicles Solar flares Correlation between solar flares and number of SEU on SAC-C KM684000 memory (Hubert et al, Multi-scale modeling to investigate the single event effects for space missions, Acta Vol 69, Is. 7-8, pp 526-536, 2011) Correlation between number of days : when >2 MeV electron fluence exceed 108cm-2sr-1 when there was an ESD switch (internal discharge) (G. Wrenn, R. Smith, Qinetiq)

Effect of particles on space vehicles Effect of solar flares on SOHO solar panel Effect of solar flares (inversed triangles) on CLUSTER solar panel power ADEOS-II failure : Debris impacted the solar panel harness which was charged due to auroras  electric arc ! Complete satellite failure on Oct 23rd 2003 (no direct link with a solar flare)

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Flare characterization SOHO/MDI magnetogram, oct 28, 2003 Mechanism : Complex loops of magnetic field near active regions Energy release with magnetic reconfiguration Possible acceleration of energetic particles (e-, p+, ions), with electromagnetic signatures in many wavelength NB. Particles events represent only a few percentage of the solar flares

Propagation in the IMF The Sun rotates with a 27 days period, creating a curved interplanetary magnetic field (Parker spiral) The charged particles ejected from a proton solar flare follow the curved magnetic lines.  Most of the flares that produce an SEPE are located in the Western visible part of the Sun. E W J.P.Vallée, Observations of the Magnetic Fields Inside and Outside the Solar System, "Fundamentals of Cosmic Physics", Vol. 19, pp. 319-422, 1998.

Measurements on Earth « Official » data provider for the X-ray and proton flux : GOES satellite (geostationary), which is an operational satellite (redundancy) Charged particles can reach Earth in various delays, from a few minutes (intense flare from well-connected active region) to a few hours (max 2 days). Depending on the presence of a CME, or the location of the flare on the solar disk, proton flux shape may differ gradual impulsive

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Customers of the service CLS forecast service was active for the 5 ESA/ATV missions (2008-2015) Critical operations of ATV w.r.t. solar flares : ATV-ISS approach ISS refueling ISS propulsion support ATV-ISS undocking ATV re-entry ESA/D. Ducros In 2013-2014, service for ESA/Gaia mission : post launch manoeuvers integration to L2 point ESA/J. Huart Since 2006, the service is also active for SSO launches ESA

Presentation of SFC service for ATV What : SEPE forecast service from CLS/SFC (Solar Forecast Center) When : Each day of the the ATV missions (from launch to re-entry). on working days: manual bulletin (with a previsionist) on week-ends: automatic bulletin, except in case of a critical operation ( human analysis) How : CLS service to provide a level of risk of a SEPE within 48h, for which the criteria were established in collaboration with the Paris Obs./LESIA, the CPTh/X, ONERA... Every day, an operator analyses the sun looking for precursors or indicators of SEPEs. They may be related to active regions morphology, position on the solar disk (Earth connection), magnetic complexity, associated electromagnetic activities (radio burst…), …

Presentation of SFC service for ATV The level of risk depends on the sensitivity of the spacecraft instruments to particles  important step = technical requirements. Example for ATV: flux critical threshold define the event: FEp+>50MeV > 10 p.f.u. (E) 4 levels of risk: NO risk Probability of (E) < 1% LOW risk Probability of (E) 1-10% MEDIUM risk Probability of (E) 10-50% HIGH risk Probability of (E) > 50%

Time distribution of SEPEs Page 16 SEPE may also occur during cycle minimum !! Eg. 1985, 2006. ATV-1 ATV-2 ATV-5 ATV-3 ATV-4

Forecast & indicators analysis EXAMPLE OF A WEEKLY SYNOPTIC : small variations of proton fluxes Favorable longitude for the first SEPE. Effect of flare “chain reaction” for the 2nd one ? Type II or IV radio bursts every day

Far side informations Far side STEREO Helioseismology (NSO/GONG) Page 18 Far side STEREO This region which was Earth directed (#11236) on June 21 2011, was detected when it was on the far side Helioseismology (NSO/GONG)

Example of forecast bulletin

January 23rd 2012 event

June 7th 2011 event The >50 MeV proton flux reached 12 pfu (only 34 events exceeded10 pfu on the last cycle) BUT : no signs of a > 50 MeV SEPE risk

July 17th 2012: 10 MeV event NASA/SRAG : no risk CLS : high level risk

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Forecast statistics & validation 639 daily bulletins emitted between January 2012 and February 2015 17 events (50 MeV proton flux > 10 pfu in the 48 following hours) Level Forecasted probability (%) A posteriori event rate (%) None [0; 1 [ 0.0 Low [1; 10 [ 0.9 Medium [10; 50 [ 4.1 High [50; 100] 32.1

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Prediction of ATV exposition to particles Goal : identify the hour of passes of the ISS in the zones exposed to particles. How ? 1/ Estimation of a worst case energy (Halloween event) corresponding to a 10 pfu flux. risk ! 10 pfu@>75MeV = ATV threshold of sensitivity to particles

Prediction of ATV exposition to particles 2/ Identify the geographical zone on a energy cutoff* map. We used the equations from « Adams, J., Letaw, J. & Smart, D., 1983. Cosmic ray effects on microelectronics part II: The Geomagnetic cutoff effects » Max lat of ISS Min lat of ISS 3/ Compute the hours of passes in these zones thanks to the ISS ephemeris (from ATV-CC) * Cutoff energy : minimum energy needed for a particle to reach a given point of the Earth environment (depends on the altitude)

Prediction of ATV exposition to particles No risk of solar particles reaching ATV when cutoff is high : The geomagnetic field blocks the dangerous part of the SEPE spectrum (proton flux > 10 pfu) Risk of solar particles reaching ATV when cutoff is low : The visible part of the SEPE spectrum includes > 50 MeV protons at fluxes > 10 pfu

Prediction of ATV exposition to particles Low geomagnetic cutoff periods of the following 2 days : Windows of a few minutes corresponding to passes over North America and South Indian Ocean Windows groups over a few hours each day UT times of beginning and end of windows groups The color of windows is adaptating to the predicted risk level of SEPE

Summary Effect of particles on space vehicles Flare characterization Presentation of the service Forecast validation for ATV-3/4/5 Improvements for ATV-4/5 Other possible improvements

Other possible improvements Inputs sources: Use of radio bursts information in real time (Nançay radioheliographs) Historical data (GOES protons flux up to cycle 21) Ions wrt protons (distribution, density) Algorithm : Before SEPEs start After SEPEs start (SOLPENCO) Other indicator : confinement or SXR-SEP peak flux (Klein et al), CME conditions… Better understanding of some particular flare mechanism (ex: June 7th 2011 event)