Space Weather Workshop Rydges Sydney Central, 3 Dec 2015 Space Weather Service Satellite and SATCOM Effects Dave Neudegg
Overview • Communications from/to satellites may be degraded by the ionosphere – especially near equatorial • Spacecraft operate in a radiation environment that is always changing • Multiple radiations issues can arise – not always interrelated • Effects depend heavily on the spacecraft design and location • Space weather support services are somewhat R&D
Satellite Communications - SATCOM • Radio signals are UHF/SHF (300MHz +, usually GHz) and pass through the electrically charged plasmasphere and ionosphere with very small angular deviation. • During disturbed ionosphere, radio ‘scintillation’ may occur. Rapid fluctuations in signal phase and amplitude. • Increased bit error rates (BER) for digital systems and distortion for analogue. Less or no throughput, so more expensive to run the circuit. • Standard scintillation index is S4 (square-root of the normalised variance of signal intensity over a given interval of time) • Most significant at low (near equatorial) and high (polar) latitudes. • Weak scintillation in most of solar cycle 24 but increased in late 2015 near end of maximum. • No reported problems from operators. But do they know if they have suffered higher BER due to scintillation?
Scintillation Effects SATCOM MESSAGE ERRORS 15 SATCOM Message 064. THE QUICK BROWN FOX JUMPS OVER THE LAZY DOGS BACK 01234567<9"TI Ascension Island 12 ?65.( VHE UUicK vROWN$GOX JUMPS OVER†THE!McZY(f~d¸z.9g?_f_}_ j›sSL 33 6 April 1997 s %E QUICK$BROWN(FOX JUM‘S OVER THE0L— ZY ?OGS ‚— CK 0123456789 TIÌU¤M ?67. (THE QUKcK BROWN GOY"JUMPS _V˜Z ™‰.O ÁOx'??.9 :c™l???0SsQJ.ª:.$~ $ U ¶S?IcK0 SˆN …? MUM“Û!_VGS* THE LAZY DOGS BACK 01=3456789 TIMES 9 Relative Signal Strength (dB) 069. THE QUICK BROWN FOX JUMPS OVER THE LAZY DOGS BACK 0123456789 TIM 6 3 Average Signal Level 0 -3 -7 Receiver Fade Margin -9 -12 00:21:00 00:22:00 00:23:00 Universal Time (hh:mm:ss) Thanks to T.Bogdan (NOAA) for S. Basu, private communication
Important latitudes for SATCOM/SATNAV effects Low latitude/Equatorial equatorial fountain, sub-equatorial anomalies. Mid-latitudes Sub-equatorial anomalies/crests High-latitudes/auroral/sub-auroral Strong gradients around auroral zone. Big storm response. M. Terkildsen
SWS SATCOM services SUBJ: IPS SCINTILLATION ALERT ISSUED AT 07:38UT Email alerts 07 Oct 2015 BY IPS RADIO AND SPACE SERVICES AREA AFFECTED: NIUE Ionospheric scintillation has been detected in the IPS ionospheric scintillation monitor located at Niue. Satellite communication and navigation may be adversely impacted near this location. To see more details of this event please go to the scintillation events page at http://www.ips.gov.au/Satellite/1/3 and the scintillation map at http://www.ips.gov.au/Satellite/1/2. Web pages
Spacecraft Environment • GEO (geostationary – 36,000km), MEO (medium earth orbit – low 20,000km) and LEO (low earth orbit <2000km) are different radiation environments • GEO = communications, weather; MEO = navigation; LEO = weather, remote sensing, recon COMSATS cost ~$1-200M each, ~400 at GEO, weather/remote sensing sats cost $3- 400M each • GEO and MEO in the radiation belts. Active during geomagnetic storms. Both protons and electrons a problem. • LEO polar orbit passes through auroral ‘field -aligned- currents’ • LEO susceptible to ‘ South Atlantic anomaly ’ enhanced radiation due to magnetic field offset • Solar Proton Events • High energy solar electrons
Primary Spacecraft Effects (a) Single Event Upset (SEU) Direct electronic circuit penetration by high energy protons or heavier ions. ‘ Solar Energetic P articles’ (SEPs) reach Earth in 1 -4 hours and can penetrate deep into the geomagnetic field, affecting at least GEO/MEO and sometimes LEO. (b) Deep Dielectric Discharge (DDD) (bulk charging) Relativistic electrons (> 1~2 MeV) penetrate and accumulate in dielectrics either outside the satellite (cables, thermal blankets, or power panel structure) or inside (circuit boards), and discharge (DDD) with destructive effect. (e.g. Equator-S) (c) Surface Charging Differential voltages on satellite outer surface due to (1) cloud of thermal energy electrons (~10-15 Kev), or (2) change that interrupts the balance of charge (orbital eclipse or structural shadowing). Changes in reference voltages that trigger circuits (Phantom Commands), or generate destructive electrostatic discharges.
S4 SEUs probable S3 S2 S1 Maximum >10 MeV flux = 24,000 pfu, 4 th highest intensity event since 1976
Satellite Anomalies: 14-16 July 2000 Proton Event & Geomagnetic Storm GEO – orientation problems during magnetopause crossing • • GEO Satellites lost ~0.1 amp output from solar arrays • LEO Satellites affected – deep penetration into geomagnetic field. • ASCA (Advanced Satellite for Cosmology and Astrophysics) – lost attitude fix resulting in solar array misalignment and power loss, satellite probably lost • GOES-8 & -10 – SEM Electron sensor problems, power panels • ACE (Advanced Composition Explorer) – Temporary SW and other sensor problems WIND – Permanent (25%) loss of primary transmitter power & Temporary loss of Sun and star • sensors SOHO (also YOHKOH & TRACE ) – High energy protons obscure solar imagery • Many anomalies caused by SEUs
SWS Severe Event Service • Predicts when a flare occurs, if an associated CME is likely to cause a severe geomagnetic storm (Dst < -250 nT). • email warning from [Ips-esws-general] Severe space weather WATCH • Associated Solar Energetic Particles? • Radiation belt energisation? Severe space weather WATCH Issued at 0438 UT on 22 Jun 2015 by IPS Radio and Space Services from the Australian Space Forecast Centre A recent Coronal Mass Ejection associated with a solar flare is anticipated to impact the Earth within the next 48 hours. The effects are expected to be significant. Increased awareness of critical infrastructure is advised. Solar Energetic Particle (SEP) Prediction • ARC Linkage Grant bid with University of Sydney Solar Physics • Magnetic mapping technique between the Earth and Sun allows us to accurately predict the occurrence and properties of SEP events at Earth.
Deep Dielectric Discharge (DDD) not just a a threat at Solar Max • Enhanced velocity solar wind streams emerge from ‘coronal hole’ regions and spread outward from Sun in the “Parker Spiral” pattern. • As the streams sweep past Earth, they inject a greater volume of higher-speed electrons. • Most often seen during years of low or declining sunspot number. • During the first 24-hours of recurrent geomagnetic storm, high energy (MeV) electrons at GEO drop to minimum background levels. Sudden two or three order of magnitude increase in counts of electrons at energies greater than 1~2 MeV at GEO. • These are the energetic particles that cause DDD events and have been called “Killer Electrons”. Accelerated within the radiation belts by plasma waves.
Annual difference in flux of energetic electrons [Dan Baker]
SWS web service - Deep Di-electric Discharge (DDD) Algorithm by J. Kennewell, website by G. Paterson Electro ctron Fluence ce and DDD D Foreca recast st Less than 10e8 Normal Background N Greater than 10e8, less Fluence M than 5x10e8 Moderate Fluence H Greater than 5x10e8, High Fluence VF less than 10e9 Very High Fluence Greater than 10e9 Current 27 day solar rotation Previous 27 day solar rotation windows
Other web services Geosynchronous Plasma Environment Model (GEOPOT08) - Shaded nonlit spacecraft surfaces - Sunlight spacecraft surfaces (photoemission on Al) - Two-Maxwellian energy distribution (e, p) - Seasonal eclipse duration at current epoch
Relativistic Electron Forecast Model (REFM) REFM predicts the occurrence of nigh energy electrons at GEO. Plots and data are updated daily at 0010 UT. Dashed vertical lines indicate the last vertical value. http://www.swpc.noaa.gov/refm/
Secondary Spacecraft Effects Magnetopause Crossing Events (MPE) at GEO Polar electric currents at LEO: Large ‘field -aligned- currents’, electric currents travelling along geomagnetic field lines, in auroral regions. Optical Disorientation : limb sensors or star trackers lose reference when energetic particles create sparks in the viewing circuitry Solar Panel Degradation : Destructive penetration of panel active elements by high energy protons of energy > 10 MeV. Large X-rays flares can also heavily degrade solar panels (e.g. Cluster-II)
Magnetopause Crossing Events (MPE) • Usually caused by strong pulse in solar wind and southwards interplanetary magnetic field • Satellite reference field is suddenly reversed north to south and the satellite becomes disoriented. • Spacecraft subjected to the solar wind radiation environment Magnetopause GEO Australian sector LEO Earth space environment – magnetosphere-ionosphere
MPE: LOSS of ORIENTATION at GEO 31 March 2001 April 29 th 2001 was the most disturbed 24-hour period since 1932. A number of commercial GEO satellites had problems with maintaining orientation Major ‘Magnetopause Event’ (MPE)
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