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Living With a Star WorkshopLiving With a Star Workshop
Radiation Effects in Spacecraft andAircraft
Dr. Eugene NormandChief Scientist, Boeing Radiation Effects Laboratory
NASA-Goddard Space Flight Center
February 9, 2000
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Overview for Assessing Impact of SpaceOverview for Assessing Impact of SpaceEnvironment on Radiation EffectsEnvironment on Radiation Effects
Ionizing radiation is diverse, comprised of 3 main sources: Trapped belts [electrons (10 keV-5 MeV) & protons (100 keV-
500 MeV)], inner belt: e & p, outer belt-mainly electrons
Galactic Cosmic Rays (GCR) ~85% energy protons, ~13%alphas and 2% HZE, all at high energies (0.01-100 GeV/amu)
Solar energetic particle (SEP) events, mainly protons, alphasand HZE, but at much lower energies than GCR
4th source, Solar wind, very low energy protons (~1-5 keV)
Ionizing radiation can effect great variety of equipmenttypes, i.e, devices: electronics, optics, electro-optics,photovoltaics, thermal & optical coatings, MEMs, etc.
It can also effect biological systems, especially astronauts,but that won’t be dealt with in this presentation
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Overview for Assessing Impact of SpaceOverview for Assessing Impact of SpaceEnvironment on Radiation Effects-ContEnvironment on Radiation Effects-Cont’’dd
There are orders of magnitude variations in: energy of theradiation, thickness of the devices, rad capability to penetratematerials, effects that can be induced, etc.
Thus, clear need to characterize the ionizing radiation indetail at both high and low energies
accurately describe energy spectra of each rad source
better describe variation of radiation sources over time
SEP events (“solar flares”) & creation of new “belts”
Enhancements in relativistic outer belt electrons
improve existing models (NASA, NRL, USAF)
predict lifetime, operability and reliability of devices beingselected for space missions
understand human threats (Shuttle, ISS & further missions)
understand/correlate different effects by different typesradiation in various components
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Description of Three Main Types ofDescription of Three Main Types ofRadiation Effects in MicroelectronicsRadiation Effects in Microelectronics
Total Integrated Dose [TID] Cumulative effect of ionization (charge buildup) in IC leading
to a gradual degradation of electrical parameters
Single Event Effects [SEE] Disturbance of an active electronic device caused by a
single energetic particle; 4 main categories Upset (SEU) --change in logic state, e.g., bit flip in RAM
Latchup (SEL) --increase in current resulting from turningon parasitic pnpn (in CMOS devices)
Damage or burnout (SEGR & SEB) of power transistor
Functional interrupt (SEFI)- malfunctions in more complexparts sometimes as lockup, hard error, etc.
Displacement Damage Cumulative effect of displacing atoms out of their lattice
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Overview in Assessing MagnitudeOverview in Assessing Magnitudeof Radiation Effects on ICsof Radiation Effects on ICs
TID
3 main environment parameters: daily dose rate (depends on orbit altitude and inclination)
mission time (number days); also effects flare probability
shielding (by structures, reduces dose rate)
TID = daily dose rate (rad/day) _ number days
Combine with measured response of ICs (passing doselevel at which degradation is measured)
SEE
GCR Heavy Ions Composite differential particle spectrum (ion/cm_day >E)
as function of E, then transformed from E→ LET
Trapped Protons Integral or differential daily flux, p/cm_day>E
Combine with measured response of ICs (SEE vs. LET)
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Upsets in Shuttle Orbiter GPCUpsets in Shuttle Orbiter GPCComputers on Ground (1)Computers on Ground (1)
STS-37 (4/91) 1st flight with GPCs (general purpose computers) Use IMS1601 64K SRAMs (~13Mbits/GPC)
Protected by EDAC (records errors) on ground and in space
First upset in GPC memory during ground testing, 4/92
Since then, total of 14 SEUs have been recorded in the GPCsduring ground testing (13 in Orbiters, 1 in spare)
Average ground upset rate [based on total time (ETI, elapsedtime indicator) -flight time] is ~8E-12 Upset/Bit-hr Higher ground rate than for other SRAMs by factor of 4-8
Agrees w/WNR SEU measurement
Factor 1.5-2 high compared to IBM measm’t, Manassas, VA
GPC data fromTami Mitchell and Kathy Milon of KSC
Ground upsets in Shuttle Orbiter GPCs on the ground arerandom, therefore they are SEUs
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Upsets in Shuttle Orbiter GPCUpsets in Shuttle Orbiter GPCComputers on Ground (2)Computers on Ground (2)
Ground upsets in Shuttle Orbiter GPCs on the ground arerandom, therefore they are SEUs
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1
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Upsets/Orbiter
Cu
mu
lati
ve
Pro
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bil
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Poisson Distribution
Shuttle Orbiter GPCs
Poisson based on 3.25 Upsets per Orbiter
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SEU Observed in Autopilot in BoeingSEU Observed in Autopilot in BoeingCommercial AircraftCommercial Aircraft
Data obtained by Autopilot Vendor; original design had “No Bus Outputs”
Autopilot design modified to include triple-voted RAM to allow neutron SEUto be detected and corrected; occurrence of “No Bus Outputs” eliminated
Latitude vs. Altitude Autopilot SEUs
-60
-40
-20
0
20
40
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80
0 10000 20000 30000 40000 50000
Altitude (Feet)
Lati
tud
e (
Deg
rees)
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SEL Observed inSEL Observed in ERS ERS Satellite Led Satellite Ledto Failed Instrument After 6 Daysto Failed Instrument After 6 Days
PRARE instrument on ERS-1 Satellite (784 km, polar orbit), launched in 1991
Failed after 6 days, problem traced to SEL in one of 22 64Kbit SRAMs
No pre-flight testing; post-flight test indicated SRAM prone to proton-induced SEL
SEL test (60 MeV protons) gave X-Section of ~3E-9 cm_/dev, leading to meanfluence for single SEL of ~1.5 E7 p/cm_, agrees with 6-day orbit fluence
0.0E+0
5.0E+6
1.0E+7
1.5E+7
2.0E+7
2.5E+7
0 20 40 60 80 100 120
Time in Orbit, Hours
Inte
gral
Flu
ence
, p/c
m≤
E> 60 MeV
E>100 MeV
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Single Even Burnout (SEB) in PowerSingle Even Burnout (SEB) in PowerMOSFETs Observed in SpacecraftMOSFETs Observed in Spacecraft
Single event burnout (SEB) caused by GCR ions, as well as protons, has beenconcern; designers avoided problem by operating MOSFETs at highly reduced Vds
CRUX experiment on APEX satellite (360_2540 km, 70° orbit) allowed 100 & 200VMOSFETs to be cycled through high voltage range, resulting SEBs were recorded
200V 2N6798 (flight lot) was tested by Boeing at HCL, yielding proton SEB crosssections; when combined w/ orbit environment, obtain good agreement w/flight data
1E-3
1E-2
1E-1
1E+0
1E+1
170 180 190 200 210 220
Vds (V)
# S
EB
/dev
ice-
day
Calculated, Avg Lab DataObserved SEBs on APEXRates Based on Lab Data Variations
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Change in Solar Change in Solar Absorbtance Absorbtance of of AgAg/FEP/FEPThermal Coating due to Electron DoseThermal Coating due to Electron Dose
Many satellites use very thin (few mils) thermal coatings, such as silver/teflon(Ag/FEP), to control the UV absorbed and hence the temperature of satellite
As low energy electrons deposit energy in the coatings, absorptance increases
Result is higher temperature; examples of data from GEO and half-GEO satellites
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0.25
1E+6 1E+7 1E+8 1E+9
Electron Dose, Rads
Incr
ease
in
So
lar
Ab
sorp
tan
ce CRETC: e/p,UV/VUV; e Fluence OnlyP-78 Data, Fit by Hall/FoteNavstar 5, Therm Expt DataNavstar 1, Battery DataNavstar 1, 1.5◊ Nom. Flux
CRETC-Lab data
P78 - GEO orbit
Navstar - 20,000 km, 63° orbit
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ConclusionsConclusions
We have shown diverse effects measured in satellites, as well as airplanes andon ground, examples of impact ionizing radiation can have on materials
Most effects have been in electronics, but have also shown effect in very thinmaterials such as thermal coating (silver/teflon, Ag/FEP)
Many other speakers will be providing other examples of the effects ofionizing radiation and our attempts to measure it in space, and incorporatethat information into useful models of the space radiation environment
As we improve our understand the space radiation environment, the better wewill be able to understand and plan for its effect on the equipment that wewill be sending into space
The Living With A Star spacecraft constellation represents a uniqueopportunity for basic science experts to join forces with applied scienceresearchers to make measurements that will be useful and meaningful to bothconstituencies