Space Weather Effectsand Prediction
CSI 662 / ASTR 769 Lect. 13 Spring 2007
May 01, 2007
References:
•Presentation (main)•Tascione: Chap. 9, Chap. 10, P. 113 – 144 (supplement)
Topics
• Space Weather Effects• Effects on Spacecraft• Radiation Health Hazard• Effects on ground-based technological systems• Effects on communications and navigations
• Space Weather Prediction and Forecasting
Space Weather Effects
Effects on Spacecraft• Spacecraft Charging• Deep Dielectric Charging• Single Event Effect (SEE)
• Single Event Upset (SEU)• Single Event Latchup
• Spacecraft dragging
Spacecraft Electric Charging• A variation in the electrostatic potential of a spacecraft
surface with respect to the surrounding plasma• A resulted electronic discharging causes problems
• Spurious electronic switching• Breakdown of thermal coating• Solar cell degradation• Optical sensor degradation
• Problems at high altitude (>5 RE), geosynchronous orbit • Caused by magnetotail particle (hot plasma, ~ Kev))
Spacecraft Electric ChargingElectric charging mechanisms
1. Particle bombardment• electron (~Kev) penetrating
~micron into a dielectric skin and stick in negative charge buildup
• In a thermal plasma, electrons move faster; more effective than protons on charging
Spacecraft Electric ChargingElectric charging mechanisms
2. Photoelectric effects• Electrons escape from the surface positive charge
buildup on the surface
The effect of these mechanisms strongly depends on the shape of the spacecraft and the material on the surface.
Responsible for about half of all spacecraft anomolies
Engineer: design discharge-resistant vehicles
Deep Dielectric Charging• Caused by energetic (relativistic) electrons (2-10 Mev) that
penetrate deep into the surface• Uneven electric potential between different portions of the
inside surface of satellites• Resulting discharging can arc directly into the satellite’s
internal electrical circuits • Resulting discharging damages the material
Probably caused altitude control problems for GEO satellites Intelsat K, Anik E-1 and Anik E-2 on Jan. 21st and 22nd following a CME
Satellite Disorientation• Some Altitude control systems are guided by specific star
patterns with the field of view• SEP particle storm produces numerous flashes of light in the
optical sensor and confuses the control system• Loss of communication• Loss of satellite power by misalignment of solar panels
Single Event Effect (SEE)• Caused by energetic particles and ions (>30 Mev) penetrates
spacecraft shielding and interact with the microelectronics (integrated circuits, ICs).
• Particles cause direct ionization of silicon materials, producing a burst of electrons
• Single Event Upset (SEU)• flips the logic state of a single bit (bit flip)• Rewrite the memory or reboot the system
• Single Event Latchup (SEL)• Lead to a permanent high state• Disable the IC
Single Event Effect (SEE)• Particle sources
1. Galactic cosmic ray (GCR)2. Solar energetic particles (SEPs)3. Radiation belt particles
• More SEE events in South Atlantic Anomaly Region
SAA
Galactic Cosmic Ray (GCR)• Produced by supernova explosion• Mostly particles in Gev, but up to 1021 ev• Isotropically• constant
Solar Energetic Particles (SEP)• Accelerated by CME-driven shocks and flare-related
magnetic reconnection• Typically 10 Mev to 1 Gev, but up to 100 Gev• Directional nature, more flux if particle path is well-
connected by interplanetary magnetic field• Last a few days• Solar cycle variation
Astronauts experience “irritating” flashes in the eyes
Single Event Effects• Various unplanned events due to faulty commands• Central processing unit (CPU) to halt• Damage to memory
Engineer design: •Error detection and correction (EDAC), additional bit•Memory redundancy
Spacecraft Drag• Frictional drag force by atmospheric particles acting on the
Low-Earth-Orbit (LEO) satellites• Decrease velocity at perigee results in a decrease in apogee
height; orbit becomes more circular• Circular orbits experience the drag at all points; faster orbit
decay
SMM orbit decay
• The drag force is
• CD = drag coefficient– Accounts for
• Momentum transfer on all sides
• Fluid flow around satellite
• Turbulent effects
– Is a function of speed, shape,
air composition, and aerodynamic environment
– CD = 2.2 for a spherical satellite around 200 km
2D D
1F C Aρ v
2
D
2
2D
dLF
dtdL ρA dx v
dx vdt
dL ρAv dt
F ρAv
F = rate of changeof momentum, L
= air density in AdxA = satellite front surface areav = satellite velocity
dx
A
v mass
Spacecraft Drag
Spacecraft Drag• Abnormally large drag results in sudden orbit changes• Tracking of objects are lost• Accurate pointing becomes difficult; accurate pointing is
important for satellite constellations• Heating and expansion during a geomagnetic storm• Heating and expansion by EUV and X-ray emission of strong
solar flares
Increased air drag caused the failure of ASCA (Advanced Satellites for Cosmology and Astrophysics) in July 2000. Extra spin moved the solar panel out of proper alignment and reduced the ability to generate power
Tracking of thousands of space object was lost during the March 13 and 14, 1989 geomagnetic storms. US commands has to re-track these objects.
Radiation Health Hazard• When very high energy particles encounter atoms or
molecules within the human body, the collisions cause a release of radiation (Bremstrahlung radiation).
• The radiation ionizes the surrounding materials, producing a region of dense ionization along its track.
• Ionizing radiation can break chemical bonds in biological molecules which result in biological injury.
• Radiation exposure results in acute, delayed, or chronic illness, depending on the rate and the accumulative dosage
• A person may suffer loss of appetite, digestive failure, brain damage and even death
Radiation Health HazardQuantify the radiation dose
Old and SI Unites of Radiation
Old Unit SI Unit
Deposition 1 rad = 10 mJ/kg 1 Gray (Gy) = 100 rad = 1 J/kg
Equivalent dose Rem=RBE X rad 1 Sievert (Sv) = quality Factor (QF) X Gray
•rad: radiation absorbed dose•RBE: relative biological effectiveness, 1.0 (200 Kev gamma ray, 2.0 (protons)
Radiation Health Hazard
Recommended Limits to Radiation Exposure
ExposureMaximum Dose (Sv)
Equivalent Dose (rem)
Astronaut Exposure 50 mSv in one year ~5 rem in one year
Public Exposure in the US
5 mSv in one year ~0.5 rem in one year
Occupational Exposure
50 mSv in one year ~5 rem in one year
Early-fetus Exposure 0.5 mSv/month ~0.05 rem in one month
Typical Chest X-ray 0.05-0.01 mSv ~0.005-0.001 rem
Natural Background ~1 mSv in one year ~0.1 rem in one year
Radiation Health Hazard• Earth’s magnetic field produces a factor of ~ ten reduction in
total GCR exposure for LEO, e.g., International Space Station orbit
• Unshielded interplanetary dose to the blood forming organs (BFO) is ~ 0.6 Sv/year, exceeding the acceptable value
• Solar energetic particles pose the greatest short-term threat to astronauts.
Radiation Health Hazard• Thin to moderate shielding is effective in reducing the
projected equivalent dose rate.• As shield thickness increases, shield effectiveness drops,
because of the large number of secondary particles
Radiation Health Hazard• Space suit has a small amount of aluminum: stops 10 Mev
protons; no extra-vehicle activity during the storm time• Spacecraft typically have several g/cm2 of aluminum
shielding.• Storm shelters, ~20g/cm2 or 200 kg/m2 of water equivalent
material,
Radiation hazard is also a concern for airlines that fly commercial flights routinely over the polar cap.
Effects of GICGeomagnetically Induced Currents (GIC)
• During space weather disturbance, enhancement of ionospheric current induces the change of geomagnetic field
• The change of geomagnetic field in turn induced a disturbance geo-electric field
• This induced electric field drives electric currents in ground-based technological systems
• Currents flow through artificial conductors present on the surface• Extended Electric power lines• Telecommunication cables• Extended pipelines• Railway lines
Effects of GICPower System
• GIC is a quasi-direct current (DC) (variation in order of minutes) compared with the 50/60Hz alternating current (AC)
• GIC flowing through a transformer winding produces extra magnetization
• A saturated transform converts energy to heat, then reducing the energy for transmission, and in turn, reducing the voltage
• Leading to trip-outs of individual lines to the collapse of the entire system
Transformer Failure in March 13-14, 1989 storm, New Jersey
Effects of GICPower System
On March 13, 1989, a GIC induced by a great geomagnetic storm caused a nine-hour blackout of the 21GW Hydro Quebec power system, leaving six million costumers without power. “Domino” effect in the collapse of a power system
Disaster could be avoided by the preventative actions taken by power grid managers
Effects of GICPipelines
• GIC causes corrosion at points where current flows from the pine into the surrounding soil
Effects on Communicationand Navigation
Instead of on hardware, this is the effect on signals of radio waves
• Radio wave transmission noise• Attenuation• Interruption• Path decay• Scintillation
Radio Wave Propagation Mode
Sudden Ionospheric Disturbance (SID)
• Associated with strong solar flares
• Penetration of flare X-rays causes the enhancement density in the D and lower E regions
• Results in sharp fadeout of long distance, radio communication on the sunlit side of the Earth
• Short lived, ~ 1 hour
Polar Cap Absorption (PCA)• Caused by energetic
protons from SEP events• Particles guided by open
field lines into the polar cap
• Increase electron density between 55 and 90 km
• Results in communication blackout
• PCA is a long-lived effect, ranging from tens of hours to several days
Communication blackout in polar cap region
Satellite Communication (Satcom)
• Use UHF (>300 Mhz) and SHF band to mitigate the ionospheric effects
• Primary long-distance communication method since 1970s• Space weather effect on SATCOM
• Scintillation in amplitude and phase
Scintillation
• Scintillation: rapid, usually random variation of the amplitude and phase of transionospheric radiowaves
• It is due to abrupt variation in electron density along the signal path which produce rapid signal path variation (phase) and defocusing (amplitude)
• It is caused by instability and turbulence• When signal fades exceed the receiver’s fade margin, the
signal is temporarily lost
Scintillation• Most significant variations occur near the F2-peak between
225 km and 400 km• The scintillation effects are most pronounced in the equatorial
(± 20 deg) geomagnetic latitude belt.• It attains maximum density between 2100 L to 0200 L time• The phenomena may persist for 20 minutes to 2 hours at a
location
Satellite Navigation
GNSS: (Global Navigation Satellite System)– GPS (Global Positioning System)– WAAS (Wide Area Augmentation System)
• Enroute Oceanic & Domestic• Terminal• Approach (down to category 1 precision)
– LAAS (Local Area Augmentation System)• Approach (category 2/3 precision)• Surface (landing)
Satellite Navigation
Satellite Navigation
• Primary Effects on GPS and related systems– Scintillation in amplitude and phase at high
latitudes and equatorial latitudes– Time delay and phase distortions arising from
the TEC (Total Electron Content) of the ionosphere
GPS Errors due to Scintillation
Propagation Effects & TEC
Effect Units FormulaeFaraday Rotation Radians 2.97 x 10-2 f -2 HL * TEC
Group-Path-Delay Seconds 1.34 x 10-7 f -2 * TEC
Phase Advance Radians 8.44 x 10-7 f -1 * TEC
Doppler Shift Hz 1.34 x 10-7 f -2 * d/dt TEC
Time Delay Dispersion
Seconds/Hz -2.68 x 10-7 f -3 * TEC
Phase Dispersion Radians/Hz -8.44 x 10-7 f -2 * TEC
MKS units are employed. The TEC is in units of electrons/square meter along the ray path, f is the radio frequency (Hz), and HL is the component of the magnetic field along the ray path
(ampere-turns/meter).
Dual frequency receiver may count for the TEC variation
Space Weather Forecasting• Forecast Timeframes• Nowcast: 0 -- 2 hr• Short-term: >2 -- 36 hr• Mid-term: > 36 -- 120 hr• Intermediate term: 5 days – several solar rotation• Long-range: > several solar rotation to solar cycle
Space Weather Forecasting• Compared with the terrestrial forecasting, space weather
forecasting is still in its infancy.• Terrestrial weather data assimilation
• Every 6 hours, measurement of about 10 different parameters taken at 104 to 105 observing points, which are interpolated onto more than 106 points of a three-dimensional grid used by numerical prediction model
• Space weather data• Data are sparse, one point outside the magnetosphere (L1),
only several points inside the magnetosphere
Example
Wang-Sheeley-Arge solar wind model:
Using photospheric surface magnetic field as a boundary condition to predict solar wind speed
ExampleBaker et al [1990] model: forecast > 2 Mev electron
at geosynchronous orbit one day in advance
Input: solar wind
Space Weather Forecasting
• NOAA Space Weather Environment Centerhttp://www.sec.noaa.gov
• NASA Community Coordinated Modeling Centerhttp://ccmc.gsfc.nasa.gov
The End