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