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Variations in the Radiation Environment

Variations in the Radiation Environment. J. L. Barth NASA/GSFC. C. D. Gorsky SGT, Inc. Introduction. A programmatic methodology for enabling COTS and emerging technology use in radiation environments requires an accurate definition of the environment with appropriate design margins.

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Variations in the Radiation Environment

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  1. Variations in the Radiation Environment J. L. Barth NASA/GSFC C. D. Gorsky SGT, Inc.

  2. Introduction • A programmatic methodology for enabling COTS and emerging technology use in radiation environments requires an accurate definition of the environment with appropriate design margins. • Variations in the environment are presented. • Limitations of radiation environment models are presented with methods of extending their functionality.

  3. The Radiation Environment Galactic Cosmic Rays Solar Protons & Heavier Ions Trapped Particles Nikkei Science, Inc. of Japan, by K. Endo

  4. Components of the Natural Environment • Transient • Galactic Cosmic Rays • Protons & Heavier Ions • Solar Particle Events • Protons & Heavier Ions • Trapped • Electrons, Protons, & Heavier Ions • Atmospheric & Terrestrial Secondaries • Neutrons

  5. Radiation Effects • Displacement Damage • Protons • Electrons • Spacecraft Charging • Surface • Plasma • Deep Dielectric • High Energy Electrons • Background Interference on Instruments • Total Ionizing Dose • Trapped Protons & Electrons • Solar Protons • Single Event Effects • Protons • Trapped • Solar • Heavier Ions • Galactic Cosmic Rays • Solar Events • Neutrons

  6. Programmatic Methodologyref: LaBel et al. IEEE/NSREC 1998 • Define the hazard • Evaluate the hazard (e.g., dose-depth curves) • Define requirements • Evaluate parts lists • Test unknowns or perform radiation lot acceptance tests (RLATs) on non-RH guaranteed devices • Evaluate test data and predict performance • Work with designers on alternate device selection or mitigation options/validation • Refine above as necessary • 3-D analysis of shielding rather than dose-depth curves • Select harder part

  7. Environment Definition for Programmatic Methodology • Displacement Damage • Energy Spectra • Shielded Solar Protons • Shielded Trapped Protons • Charging/Discharging • Surface - Plasma Electrons • Deep-dielectric - High Energy Electrons • Instrument Interference • Primary Particles • Secondary Particles - Shielding Analysis • Total Ionizing Dose • Dose-Depth Curves or Spacecraft Specific Dose Levels • Trapped Protons & Electrons • Solar Protons • Secondary Bremsstrahlung • Single Event Effects - Average & Peak Conditions • LET Spectra • Galactic Cosmic Ray Heavy Ions • Solar Heavy Ions • Energy Spectra • Solar Protons • Trapped Protons

  8. Sun Source Modulator Protons Galactic Cosmic Rays Atmospheric Neutrons Heavier Ions Trapped Particles Trapped Particles Sun:Dominates the Environment

  9. 300 250 200 150 100 50 0 SolarFlares SolarActivity:CyclicVariation • Sunspot Cycle Discovered in mid 1800s • Coronal Mass Ejections • Increase in Solar Wind Velocity • Solar Particle Events - Proton Rich • Solar Flares • Increase in Solar Wind Density • Solar Particle Events - Heavy Ion Rich Sunspot Cycle CoronalMassEjections Cycle 19 Cycle 20 Cycle 21 Cycle 22 Cycle 18 Sunspot Numbers Holloman AFB/SOON Years after Lund Observatory

  10. The Magnetosphere • Defined by Interaction of: Earth’s Magnetic Field - Solar Wind • Solar Direction: Compressed to ~ 10 ER • Anti-Solar Direction: Stretched into Long Magnetotail ~ 300 Earth Radii • Open at the Poles • Bar Magnet Representation Accurate to 4 - 5 Earth Radii

  11. Magnetosphere Bow Shock Cusp Central Plasma Sheet Magnetopause Solar Wind Heikkila (Color by University of Washington)

  12. Particle Penetration of the Magnetosphere • Most Solar Wind Particles Are Deflected (99.9%) • Some Become Trapped & Energized • Galactic Cosmic Ray & Solar Particle Penetration Depends on: • Particle Energy • Ionization State • Galactic Fully Ionized • Solar & Anomalous Component of GCRs Have Lower Ionization States • Measured with Magnetic Rigidity in Units of GV

  13. momentum charge 2 3 4 5 6 7 Magnetic Rigidity Total Energy Required to Penetrate the Magnetosphere H 48 MeV 87 MeV 173 MeV 284 MeV 987 MeV Magnetic Equator 2900 MeV 1147 MeV/n 313 MeV/n 109 MeV/n 46 MeV/n 23 MeV/n 12 MeV/n Z > 1 after Stassinopoulos

  14. Magnetic Storms / Space Weather • “Gusty” Solar Wind Disturbs the Current Systems • Major Storms Probably the Result of CMEs • Must Be Pointed Toward Earth • Strongest Arrive with Interplanetary Magnetic Field Oriented South • Can Have Severe Effects • Power Blackouts on Earth • Disruption of Communications Satellites • Loss of Satellites - ANIK-E1, Telstar 401

  15. Sunspot Cycle with Magnetic Storms Sunspots & Magnetic Storm Days # of Days with Ap > 4 Sunspot Number Annual Sunspot Number Annual Number of Days with Ap>4

  16. 800 7 700 6 600 5 4 500 3 400 2 300 1 0 200 1 6 11 16 21 25 31 1 6 11 16 21 25 31 ANIK E1: Magnetic Storm Solar Wind Velocity (IMP-8 MIT) SAMPEX Electrons E > 1 MeV 8 Time of ANIK Failure Counts/s (x10) Velocity (km/s) January 1994

  17. Trapped - Van Allen Belts • Omnidirectional • Components • Protons: E ~ .04 - 500 MeV • Electrons: E ~ .04 - 7(?) MeV • Heavier Ions: Low E - Non-problem for Electronics • Location of Peak Levels Depends on Energy • Average Counts Vary Slowly with the Solar Cycle • Location of Populations Shifts with Time • Counts Can Increase by Orders of Magnitude During Magnetic Storms • March 1991 Storm - Increases Were Long Term • Radiation Effects • Dose & Degradation • Single Event Effects - Protons only • Models - AP8/NOAAPRO & AE8

  18. Van Allen Belts High Latitude Horns Inner Belt Slot Region BIRA/IASB Outer Belt

  19. 4 3 2 1 1 2 3 4 5 6 7 8 9 10 Proton & Electron Average Models AP-8 Model AE-8 Model Ep > 10 MeV Ee > 1 MeV #/cm2/sec #/cm2/sec L-Shell NASA/GSFC

  20. Protons Trapped Particle Variations Electrons • Cyclic Modulation Due to the Solar Cycle ~ 2 • Highest Levels Are at Peak of Solar Maximum • Lowest Levels Are at Lowest Point in Solar Minimum • Inner Zone - Fairly Stable • Outer Zone - Dynamic 102 ~ 106 • Solar Cycle Variations Are Masked • Local Time Variations Due to Magnetic Field Distortion • 27-Day Variation Due to Solar Rotation • Magnetic Storms & Sub-Storms • Fairly Stable • Cyclic Modulations Due to the Solar Cycle ~ 2 • Lowest Levels Are at Peak of Solar Maximum • Highest Levels Are at Lowest Point in Solar Minimum • Rate of Change ~ 6%/year • Geomagnetic Field Shift Changes Location • ~ 6 ° westward / 20 years • Anisotropy at Inner Edge (300-500 km) 2 ~ 7 • Particle Increases at Outer Edge - New Belts • Geomagnetic Storms

  21. TIROS/NOAA Trapped Protons Solar Cycle Variation: 80-215 MeV Protons B/Bmin=1.0 L=1.20 L=1.18 L=1.16 Radio Flux F 10.7 Proton Flux (#/cm2/s) L=1.14 1976 1980 1984 1988 1992 1996 Date Huston et al.

  22. March 1991 Magnetic StormNew Proton Belt CRRES - AF Phillips Laboratory, SPD/GD

  23. 11 9 7 5 3 1 190 250 310 370 430 490 550 Activity in the Slot Region - SAMPEX SAMPEX/P1ADC: Electrons E > 0.4 MeV L-Shell Day (1992)

  24. 6 4 2 1990 1991 1992 March Magnetic Storms - Hipparcos Star Mapper - Radiation Background L-Shell 4-Day, 9-Orbit Averages Daly, et al.

  25. Protons in SAA - 800 km Proton Flux Contours • Variations with Altitude • At 800 km, SAA is an oval shape • At 1300 km, the size of the oval shape increases • At 3000 km, Van Allen “belt” structure of proton flux contours Latitude (deg) Longitude (deg) Protons in SAA - 1300 km Protons in SAA - 3000 km Latitude (deg) Latitude (deg) Longitude (deg) Longitude (deg)

  26. AP8 - MAX Spectra Integral Proton Fluences • Energy Range • .04 - 500 MeV • Range in Al: • 30 MeV ~ .17 inch • Effects: • Total Dose • Single Event Effects • Solar Cell Damage Fluence (#/cm2/day) Energy (>MeV)

  27. AE-8 - MAX Spectra Integral Electron Fluences • Energy Range • .04 - 7 MeV • Range in Al: • Effects: • Total Dose • Surface Charging • Deep Dielectric Charging • Solar Cell Damage Fluence (#/cm2/day) Energy (>MeV)

  28. Single Event Effects - Proton Rates I=90 deg, H=1000/1000 km, Solar Minimum • Trapped proton exposure in LEO depends on where satellite passes through the SAA • Calculate SEE rates for • Proton daily average • Worst case SAA pass • Peak proton counts in SAA • Implications for memory scrub rates & other spacecraft operations Protons (#/cm2/s) Energy (>MeV)

  29. Particle Variations • Protons and Photons • extremely penetrating • difficult to shield against • Electrons • lower energies make them less penetrating

  30. Dose Variation with Altitude0 degree inclination

  31. Dose Variation with Altitude90 degree inclination

  32. Dose-Depth CurvesDose Variation with Orbit • Use “Dose-Depth Curves” to define top level dose requirements • “Total Dose” includes contributions from • Trapped protons • Trapped electrons • Solar protons • Minimum design margin of “x2” added to account for uncertainty in environment models and variation of device response within flight lots

  33. Galactic Cosmic Ray Ions • All Elements in Periodic Table • Energies in GeV • Found Everywhere in Interplanetary Space • Omnidirectional • Mostly Fully Ionized • Cyclic Variation in Fluence Levels • Lowest Levels = Solar Maximum Peak • Highest Levels = Lowest Point in Solar Minimum • Single Event Effects Hazard • Model: CREME96

  34. GCRs: Solar Modulation Galactic Cosmic Rays CNO - 24 Hour Averaged Mean Exposure Flux Solar events • Long term cyclic variation • Peak at solar minimum • Shielding ineffective for high energy ions • Attenuation by magnetosphere effective for low inclination, low altitude orbits CNO (#/cm2/ster/s/MeV/n) Years GCRs: Shielded Fluences - Fe GCRs: Integral LET Spectra Interplanetary, CREME 96, Solar Minimum CREME 96, Solar Minimum, 100 mils (2.54 mm) Al Particles (#/cm2/day/MeV/n) LET Fluence (#/cm2/day) Energy (MeV/n) LET (MeV-cm2/mg)

  35. Solar Particle Events • Increased Levels of Protons & Heavier Ions • Energies • Protons - 100s of MeV • Heavier Ions - 100s of GeV • Abundances Dependent on Radial Distance from Sun • Partially Ionized - Greater Ability to Penetrate Magnetosphere • Number & Intensity of Events Increases Dramatically During Solar Maximum • Problem for Total Ionizing Dose, Displacement Damage, & Single Event Effects • Models • Dose & Displacement Damage - SOLPRO, JPL, ESP • Single Event Effects - CREME96 (Protons & Heavier Ions)

  36. Sunspot Cycle with Solar Proton Events Proton Event Fluences Solar Proton Events • Solar proton events correlate with the sunspot cycle • Only low inclination, low altitude orbits are protected from solar proton events • A problem for degradation & single event effects • ESP model by NRL/NASA Protons (#/cm2) Year Solar Protons: Orbits ESP Model of Solar Proton Cumulative Fluences Proton Levels Predicted by CREME 96 Protons (#/cm2/s/MeV) Energy (MeV)

  37. Effect of Shielding on Heavy IonsGalactic Cosmic Ray & Solar Heavy Ion Spectra Integral LET Spectra , 100 mils AL Solar Heavy Ions • Frequency & intensity increase during solar active phase of the solar cycle • Attenuation by magnetosphere effective for low inclination, low altitude orbits • Solar heavy ion levels are orders of magnitude higher than galactic cosmic ray levels • Shielding more effective than for galactic cosmic ray heavy ions LET Fluence (#/cm2/sec) LET (MeV-cm2/mg) Differences in Energy Spectra Galactic Cosmic Ray & Solar Heavy Ion Spectra All Elements, 100 mil Shield Interplametary Carbon, 100 mil Shield Interplametary Fluence (#/cm2/s) Fluence (#/cm2/s) Energy (MeV) LET (MeV-cm2/mg)

  38. Summary • Requirements for the definition of the radiation environment for a programmatic methodology were defined. • The variations in the radiation environment which must be considered in the definition were described. • Appropriate models for defining the radiation environment were presented. • References: • “Emerging Radiation Hardness Assurance (RHA) Issues: A NASA Approach for Spaceflight Programs,” K. A. LaBel, J. L. Barth, R. A. Reed, and A. H. Johnston, IEEE Trans. on N.S., December 1998. • “Applying Computer Simulation Tools to Radiation Effects Problems, Part I: Modeling Space Radiation Environments,” J. L. Barth, Published in 1997 IEEE NSREC Short Course Notes, July 1997.

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