Spacecraft Radiation Protection

Summary This two-day course provides an in-depth overview ofrisks posed by radiation to spacecraft and workingsolutions minimizing those risks. Students will gain asolid understanding of the radiation environment, itsmeasurement, its effects and effective mitigationstrategies.

Course Outline

1. Space Radiation Environment. Trappedprotons and electrons. Solar energetic particles.Cosmic rays. Neutrons and gamma rays fromRadioactive Thermoelectric Generators (RTGs).Secondary neutrons from large space structures.Mars surface and high altitude Earth enironment.

2. Total Dose and Effects. Energy per unit mass.Units--rads, REMs, Grey, Sieverts. Ionizationeffects. Charge deposition, migration and collection.Effects on digital and analog MOS and bipolardevices including ELDRS. Annealing, recovery,rebound.

3. Displacement Damage. Crystalline latticedeformations. Damage thresholds in silicon andgallium arsenide. Damage equivalence and NIEL.Effects of protons and neutrons on solar cells anddetectors such as CCDs. Dark current, chargetransfer efficiency, maximum power degradation.

4. Single Event Effects. Ionization by primaryparticles and secondaries from nuclear collisions.Charge collection in small structures. Effects indigital and analog devices. Transient and permanentupsets, soft errors, latch-up, burn-out, SEFI. Volatileand non-volatile memories, micro and signalprocessors, DC/DC converters, optoelectronics.

5. Testing and Mitigation Techniques. Totaldose testing. SEE testing. Facilities. Shielding.Derating. Conservative circuit design. Systemsmitigation. EDAC, latch-up protection circuitry, watchdog timers, autonomy.

6. Human Effects. Long duration exposure inlow Earth orbit and interplanetary transport vehicles.Threat of high-energy neutrons to astronauts.Effects in tissue and organs. Dose Equivalent andweighting factors. Risk of carcinogenesis, DNAdamage. CNS effects

Instructor Dr. Alan C. Tribble has provided space environmentseffects analysis to more than one dozen NASA, DoD,and commercial programs, including the InternationalSpace Station, the Global Positioning System (GPS)satellites, and survival surveillance spacecraft. Heholds a Ph.D. in Physics from the University of Iowaand has been twice a Principal Investigator for theNASA Space Environments and Effects Program. He isthe author of four books, including the course text: TheSpace Environment - Implications for Space Design,and over 20 additional technical publications. He is anAssociate Editor of the Journal of Spacecraft andRockets, and Associate Fellow of the AIAA and aSenior Member of the IEEE. Dr. Tribble recently wonthe 2008 AIAA James A. Van Allen SpaceEnvironments Award. He has taught a variety ofclasses at the University of Southern California,California State University Long Beach, the Universityof Iowa, and has been teaching courses on spaceenvironments and effects since 1992

• Weu

• W• H

s• H• H• H

s• H

What You Will Learn

hat the models are for spacenvironments, where to find them, how tose them. hat the common radiation units mean. ow to equate damage from differentpecies of radiation. ow to conduct total dose test. ow to conduct SEE tests. ow to use dose-depth curves in determininghield thickness. ow to shield neutrons.

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COURSE OBJECTIVE

• The purpose of this course is to characterize space (and atmospheric) radiation effects and how they are mitigated– By the end of class, you should be able to read

and follow most papers and presentations in radiation effects and know where to look for further expertise

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ABOUT THE INSTRUCTOR

• Dr. Alan Tribble– Over Twenty Years Experience in Space Environments and

Effects• Author of First Text on Space Environments & Effects• Principal Investigator for the NASA Space Environments & Effects

Program• Associate Editor for the AIAA Journal of Spacecraft and Rockets• Instructor for Space Environments & Effects Courses Since 1992

– Winner of the 2008 AIAA James A. Van Allen Award • Presented to recognize outstanding contributions to space and

planetary environment knowledge and interactions as applied to the advancement of aeronautics and astronautics.

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THE ENVIRONMENTS OF SPACE

• Vacuum Environment Effects– Phenomena Associated With the Absence of a Substantial

Atmosphere• Neutral Environment Effects

– Phenomena Associated With the Presence of a Tenuous Neutral Atmosphere

• Plasma Environment Effects– Phenomena Associated With the Presence of Low Energy (KeV

Range) Charged Particles• Radiation Environment Effects

– Phenomena Associated With the Presence of High Energy (MeV -GeV Range) Particles / Photons

• Micrometeoroid / Orbital Debris Effects– Phenomena Associated With the Presence of Hypervelocity

Particles

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RADIATION ANOMALIES

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IMPACT DURATION

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FUNDAMENTAL FORCES

• Four Forces– Strong Nuclear

• Important Near the Nucleus

– Weak Nuclear• Important Near the

Nucleus– Electrical

• Very Significant for Particles That are Charged

– Gravitational• Only Important for Very

Large Masses Nuclear Forces OnlyDominates Near theNucleus

Electrical Force AlwaysDominates Outsidethe Nucleus

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STOPPING POWER

http://en.wikipedia.org/wiki/Stopping_power_(particle_radiation)

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BRAGG PEAK

http://en.wikipedia.org/wiki/Stopping_power_(particle_radiation)

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LET VS RANGE

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Photon Energy (MeV)

Abs

orpt

ion

Coe

ffic

ient

(cm

^2/g

)

0

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1

0 .1 2

0 .1 4

0 .1 6

0 .1 8

0 .2

0 .1 1 1 0 1 0 0

Compton

Pair Production

Photoelectric

Total

10-1 100 101 102

CrossSection(cm2/g)

PHOTON CROSS SECTION

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ATMOSPHERIC NEUTRONS

• The Neutron Flux is a Function of Altitude and Latitude

• The Worst Location is a Polar Route at About 55,000 Feet

Neutron Flux vs Altitude

00.20.40.60.8

11.21.4

0 20 40 60 80 100

Altitude (Thousand Feet)

Flux

(n /

cm^2

s)

Neutron Flux vs Latitude

00.20.40.60.8

11.21.41.6

0 20 40 60 80 100

Latitude (Deg.)

Flux

(n /

cm^2

s)

Normand, E., and Baker, T. J., “Altitude and Latitude Variations in Avionics SEU and Atmospheric Neutron Flux,” IEEE Tns. Nuc. Sci., Vol. 40, No. 6, pp. 1484 - 1490, December 1993.

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EFFECTS OF INTERACTIONS

• Main Effects– Ionization (~ 99%)

• Ionizing Target Atoms Produces More Charge Carriers

– Displacement (~1%)• Lattice Atoms are Rearranged

– Absorption / Capture (< 1%)• Target Nucleus May Absorb Radiation and Re-Emit

Other Particles

• Result– Electrical and Chemical Properties of the Target

are Altered

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MEASURES OF ENERGY DEPOSITION

• Total Ionizing Dose (TID)– A Measure of the Amount

of Energy Lost Due to Ionizations

– TID is a Function of• The Radiation

– Energy and Type• The Target Material

• Displacement Damage (DD)– A Measure of the Amount

of Energy Lost Due to Displacements

– DD is a Function of • The Radiation

– Energy and Type• The Target Material

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MEASURES OF ENERGY LOSS / PATH

• Linear Energy Transfer (LET)– Measures the Amount of

Energy Lost Per Unit Path Length Due to Ionizations

• Non-Ionizing Energy Loss (NIEL)– Measures the Amount of

Energy Loss Per Unit Path Length Due to Displacements

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AREA OF REFLECTION

GEOLEO

Particle Motion

Trapping Moves Particles North - SouthDrifts Move Particles East-West

MAGNETIC TRAPPING OF THE RADIATION BELTS

GPS

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GOES SATELLITE ENVIRONMENT DATA

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• Magnetic Field Lines Entering the Atmosphere at High Latitudes Allow Charged Particles to Reach Lower Altitudes in Polar Regions

• Consequently, the Radiation Dose and Dose Rate are Increased in Polar Orbits– An Example of This is the Aurora Borealis and the Aurora

Australialis

POLAR VS EQUATORIAL

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• A Decrease in the Dipole Term of the Earth’s Magnetic Field Results in a Westward and Southward Drift of the Ground-Level Local Minimum in the Magnetic Field Known as the South Atlantic Anomaly (SAA)

• This Allows Higher Energy Particles to Reach Lower Altitudes Over the South Atlantic

SOUTH ATLANTIC ANOMALY - 1

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SOUTH ATLANTIC ANOMALY - 2

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Single Event Effects Often Maximize Over The SAA

SEU FOR ALEXIS SPACECRAFT

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SPE COMPOSITION

Large Solar Proton Event Spectra at 1 AU

1.00E+07

1.00E+08

1.00E+09

1.00E+10

1.00E+11

1 10 100 1000

Kinetic Energy (MeV)

Inte

gral

Flu

ence

, (pr

oton

s /

cm^2

)

Feb 1956Nov 1960Aug 1972Aug 1989Sep 1989Oct 1989

Wilson, J. W., Cucinotta, F. A., Simonsen, L. C., Shinn, J. L., Thibeault, S. A., and Kim, M. Y., "Galactic and Cosmic Ray Shielding in Deep Space", NASA TP 3682, December 1997

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GCR COMPOSITION

Galactic Cosmic Ray Fluence, Solar Max (1981)

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06

Kinetic Energy (A MeV)

Annu

al F

luen

ce, (

part

icle

s / c

m^2

- A

MeV

)

Z = 1Z = 2Z: 3 - 10Z: 11 - 20Z: 21 - 28

Wilson, J. W., Cucinotta, F. A., Simonsen, L. C., Shinn, J. L., Thibeault, S. A., and Kim, M. Y., "Galactic and Cosmic Ray Shielding in Deep Space", NASA TP 3682, December 1997

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MITIGATION TECHNIQUES

• Shielding– Prevent the Radiation Environment From Reaching the Crew

or Sensitive Electronics• Not Effective on Very Energetic (GeV) Charged Particles

• Parts Selection– Choose Parts or Materials That Can Withstand the Total

Dose Environment Anticipated– Choose Parts That are Immune or Resistant to SEE

• Fault Tolerance– Hardware

• Redundancy, Majority Voting, …– Software

• Error Detection and Correction (EDAC), Hamming Codes, …

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GPS Trapped Radiation: 20,000 km - 55 Deg

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11 1.00E+12 1.00E+13

Fluence (# cm ^-2 day^-1)

Ener

gy (M

eV)

Protons

Electrons - Solar Min

Electrons - Solar Max

20,000 km @ 55 degrees

104 105 106 107 108 109 1010 1011 1012 1013

Fluence (cm-2 day -1)

101

Energy(MeV)

100

10-1

10-2

Protons

Electrons - Solar Min.

Electrons - Solar Max.

GPS RADIATION ENVIRONMENT

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Altitude = 20,000 kmInclination = 55 deg.

Shielding = Full-Sphere

Shie ld ing Thic kne ss (m ils - Al)

Dos

e (r

ad/d

ay)

0.10

1.00

10.00

100.00

1000.00

10000.00

10 100 1000

To ta l

Pro to n

Ele c tro n

Bre m s.

GPS RADIATION DOSE

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DESIGN EXAMPLE: SOLAR ARRAY SIZING

• Solar Array Size is Driven by the Amount of Energy That Must be Produced– A = Solar Array Area (m2)– P = Power Required (W)– = Efficiency

• Efficiency is Degraded by Radiation– BOL Value is Greater Than the EOL Value

• Efficiency Loss is Minimized by Adding a Transparent Shield– Coverslide

– S = Sun’s Power Output (1367 W/m2 at Earth Orbit)

SPA

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TOTAL IONIZING DOSE III

• Digital Devices – Suffer threshold voltage shifts, supply current

increases and timing degradation• Linear Devices

– Experience increased input bias currents, offset voltages and offset currents as circuitry becomes unbalanced

• In worst cases functionality ceases– Particularly when the timing is affected in a VLSI

device and after many nodes information does not reach the next gate in the correct time window.

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DISPLACEMENT DAMAGE SKETCH

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• An Energetic Particle Passes Through a Semiconductor and Creates a Trail of Ionized Particles in the Vicinity of a Reverse Biased PN Junction– The Sudden Flux in Ionized Particles Can Cause

a Swing in Bias Across the Junction

– The Change May Alter the State of the Device

• This is an Example of a Single Event Effect (SEE)

SINGLE EVENT EFFECTS (SEE)

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TYPES OF EFFECTS

• Single Event Upset– Change in state of a memory element– System-level manifestations depend on application

• Single Event Latchup– Low resistance path develops between power and ground

through the device, usually destructive– Sometimes observe “mini-latch” behavior

• Single Event Functional Interrupt– Upset which places a device in an ill-defined condition– Causes system to lock up or jump into an unknown

configuration• Single Event Transient

– Spurious voltage spike that can cause system-level effects– Increased noise in the system

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TYPES OF EFFECTS

• Single Event Burnout– Localized short through power MOSFET– Permanently damages the part

• Single Event Gate Rupture– Localized short through drain-to-oxide interface in

a power MOSFET– Permanently increases gate leakage

• Single Event Dielectric Rupture– Oxide damage in non-volatile elements or anti-

fuse type FPGAs

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ION STRIKE SCHEMATIC

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VIN

VOUT

p-type substrate

n+ n+

n-well

p+ p+p+ n+

VSSVDD

Source

Gate

Drain Source

SEE ILLUSTRATION

Radiation(proton, ion, neutron, …)

Upset occurs if channel current turned on

Latchup occurs if parasitic current loop initiated

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SEU EXAMPLE: SAMSUNG DRAM

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TOTAL IONIZING DOSE (TID) TEST FLOW

• 25° C anneal– For simulation of reduction in oxide trapped charge

• 100° C anneal – For accelerated production of interface trapped charge

Irr. To Spec.50-300 rad/s

PassElec?

Irr. 50% Over50-300 rad/s

Biased Anneal168 hr @ 100C

PassElec?

Parts OK

Reject Parts

Yes

Yes

No

Biased Anneal@ 25 C

PassElec?

No

No

Yes

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ELDRS TEST FLOW

• May require extensive evaluation

Start Review DataELDRS?

TM1019or other

Accept Risk?

Initial Test1) Baseline high rate at room temp2) Compare to low rate or elev. tempELDRS?

No

No

??

Yes Yes

1) Test at 10 mrad/swith margin of 2 or2) test at 10 rad/s, 100C with margin of 3

Yes

1) Determine max low dose rate enhancement2) Elevated temperature irradiation and anneal

No

AcceptanceTest

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TEST FACILITY REQUIREMENTS

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TEST FACILITY REQUIREMENTS

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NASA INTERNET SITES

• Glenn Research Center– Space Environments and

Experiments Branch• http://www.grc.nasa.gov/WWW

/epbranch/

• Goddard Space Flight Center– Radiation Effects and Analysis

• http://radhome.gsfc.nasa.gov– National Space Science Data

Center (NSSDC)• http://nssdc.gsfc.nasa.gov

– Community Coordinated Modeling Center (CCMC)

• http://ccmc.gsfc.nasa.gov/modelweb/

• Jet Propulsion Laboratory– Radiation Effects Group

• http://parts.jpl.nasa.gov

• Johnson Space Center– Orbital Debris Program Office

• http://orbitaldebris.jsc.nasa.gov

• Langley Research Center– Space Environments and

Technology Archive System (SETAS)

• http://setas-www.larc.nasa.gov/

• Marshall Space Flight Center– Space Environments and Effects

Program• http://see.msfc.nasa.gov

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OTHER INTERNET SITES

• NOAA – Space Weather Prediction

Center• http://www.swpc.noaa.gov

• Space Weather– Science News and Information

• http://www.spaceweather.com– Space Science Institute

• http://www.spaceweathercenter.org/

• Space Environment Information System (SPENVIS)

– interface to models of the space environment and its effects, including the natural radiation belts, solar energetic particles, cosmic rays, plasmas, gases, and "micro-particles".

• www.spenvis.oma.be

• Instructor’s Web Site– Links to Site’s of Interest

• http://www.atribble.com