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

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
Trapped
Electrons, Protons, & Heavier Ions
Atmospheric & Terrestrial Secondaries
Neutrons

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

6. Programmatic Methodology ref: 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
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
Trapped Protons
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

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

9. Solar Activity: Cyclic Variation
Solar Flares
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
Coronal Mass Ejections 50
150
200
250
100
300
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 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. Magnetic Rigidity momentum charge H Z > 1
Total Energy Required to Penetrate the Magnetosphere H
48 MeV
87 MeV
173 MeV
284 MeV
987 MeV
Magnetic Equator
2900 MeV 2 3 4 5 6 7
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 Number of Days with Ap>4
Annual Sunspot Number

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

17. Trapped - Van Allen Belts
Omnidirectional
Components
Protons: E ~ MeV
Electrons: E ~ (?) 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 Outer Belt Slot Region
BIRA/IASB

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

20. Trapped Particle Variations
Protons
Electrons
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 ( km) 2 ~ 7
Particle Increases at Outer Edge - New Belts
Geomagnetic Storms
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

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

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

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

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

25. Proton Flux Contours Variations with Altitude
Protons in SAA 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 km
Protons in SAA km
Latitude (deg)
Latitude (deg)
Longitude (deg)
Longitude (deg)

26. AP8 - MAX Spectra Integral Proton Fluences Energy Range Range in Al:
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
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 Electrons
extremely penetrating
difficult to shield against
Electrons
lower energies make them less penetrating

30. Dose Variation with Altitude 0 degree inclination

31. Dose Variation with Altitude 90 degree inclination

32. Dose-Depth Curves Dose 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. 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
Effect of Shielding on Heavy Ions Galactic Cosmic Ray & Solar Heavy Ion Spectra
Carbon, 100 mil Shield
Interplametary
All Elements, 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.