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The Radiation Environmentfor theNext GenerationSpace TelescopeJanet L. BarthNASA/Goddard Space Flight CenterGreenbelt, MarylandJohn C.
IsaacsSpace Telescope Science InstituteBaltimore, MarylandChristian
PoiveySGT-Inc.Greenbelt, MarylandSeptember 2000G S F C
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2Table of ContentsI.INTRODUCTION
................................................................................................................................
3II. RADIATION ENVIRONMENT
.........................................................................................................
3III.DESCRIPTION OF RADIATION EFFECTS
...............................................................................
3IV.THE NGST
MISSION......................................................................................................................
4V. TOTAL DOSE AND
DEGRADATION..............................................................................................
5A. DEGRADATION
ENVIRONMENT............................................................................................................
61. The Plasma
Environment................................................................................................................
62. High Energy Particles Spacecraft Incident Fluences
................................................................ 123. High
Energy Particles Shielded Fluences
.................................................................................
15B. TOTAL DOSE
ESTIMATES...................................................................................................................
181. Top Level Ionizing Dose
Requirement..........................................................................................
182. Dose at Specific Spacecraft
Locations..........................................................................................
20C. DISPLACEMENT DAMAGE
ESTIMATES...............................................................................................
20VI.SINGLE EVENT EFFECTS
ANALYSIS.....................................................................................
21A. HEAVY ION INDUCED SINGLE EVENT
EFFECTS..................................................................................
211. Galactic Cosmic
Rays...................................................................................................................
212. Solar Heavy
Ions...........................................................................................................................
22B. PROTON INDUCED SINGLE EVENT
EFFECTS.......................................................................................
221. Trapped
Protons...........................................................................................................................
232. Solar
Protons................................................................................................................................
23VII. INSTRUMENT
INTERFERENCE...............................................................................................
23VIII. SPACECRAFT CHARGING AND
DISCHARGING.................................................................
28IX.SUMMARY.....................................................................................................................................
28X. REFERENCES
...................................................................................................................................
29APPENDICES...........................................................................................................................................
A-1
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3I. IntroductionThe purpose of this document is to define the radiation
environment for the evaluation of degradation dueto total ionizing and
non-ionizing dose and of single event effects (SEEs) for the Next Generation
SpaceTelescope (NGST) instruments and spacecraft. The analysis took into account
the radiation exposure forthe nominal five-year mission at the Earth-Sun L2
Point and assumes a launch date in June 2009. Thetransfer trajectory out to the
L2 position has not yet been defined, therefore, this evaluation does notinclude
the impact of passing through the Van Allen belts. Generally, transfer
trajectories do not contributeto degradation effects; however, single event
effects and deep dielectric charging effects must be taken intoconsideration
especially if critical maneuvers are planned during the Van Allen belt
passes.II. Radiation EnvironmentThe natural space radiation environment of
concern for damage to spacecraft electronics is classified intotwo populations,
1) the transient particles which include protons and heavier ions of all of the
elements ofthe periodic table, and 2) the trapped particles which include
protons, electrons and heavier ions. Thetrapped electrons have energies up to 10
MeV and the trapped protons and heavier ions have energies up to100s of MeV. The
transient radiation consists of galactic cosmic ray particles and particles from
solarevents (coronal mass ejections and flares). The cosmic rays have low level
fluxes with energies up to TeV.The solar eruptions periodically produce
energetic protons, alpha particles, heavy ions, and electrons. Thesolar protons
have energies up to 100's MeV and the heavier ions reach the GeV range. All
particles areisotropic and omnidirectional to the first order.Space also
contains low energy plasma of electrons and protons with fluxes up to
1012cm2/sec. Theplasmasphere environment and the low energy (< 0.1 MeV)
component of the charged particles are aconcern in the near-earth environment.
In the outer regions of the magnetosphere and in interplanetaryspace, the plasma
is associated with the solar wind. Because of its low energy, thin layers of
materialeasily stop the plasma so it is not a hazard to most spacecraft
electronics. However, it is damaging tosurface materials and differentials in
the plasma environment can contribute to spacecraft surface chargingand
discharging problems [1,2].III. Description of Radiation EffectsRadiation
effects that are important to consider for instrument and spacecraft design fall
roughly into threecategories: degradation from total ionizing dose (TID),
degradation from non-ionizing energy loss (NIEL),and single event effects. Total
ionizing dose in electronics is a cumulative long term ionizing damage dueto
protons and electrons. It causes threshold shifts, leakage current and timing
skews. The effect firstappears as parametric degradation of the device and
ultimately results in functional failure. It is possible toreduce TID with
shielding material that absorbs most electrons and lower energy protons. As
shielding isincreased, shielding effectiveness decreases because of the
difficulty in slowing down the higher energyprotons. When a manufacturer
advertises a part as "rad-hard", he is almost always referring to its
totalionizing dose characteristics. Rad-hard does not usually imply that the
part is hard to non-ionizing dose orsingle event effects.
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4Displacement damage is cumulative long-term non-ionizing damage due to protons,
electrons, andneutrons. The particles produce defects in optical materials that
result in charge transfer degradation. Itaffects the performance of optocouplers
(often a component in power devices), solar cells, CCDs, andlinear bipolar
devices. The effectiveness of shielding depends on the location of the device.
For example,coverglasses over solar cells reduce electron damage and proton
damage by absorbing the low energyparticles. Increasing shielding, however, is
not usually effective for optoelectronic components because thehigh-energy
protons penetrate the most feasible spacecraft electronic enclosures. For
detectors ininstruments it is necessary to understand the instrument geometry to
determine the vulnerability to theenvironment.Single event effects are caused
through ionization by a single charged particle as it passes through asensitive
junction of an electronic device. They are caused by heavier ions, but for some
devices, protonscan induce single event effects. In some cases SEEs are induced
through direct ionization by the proton,but in most instances, proton induced
effects are the result of secondary particles that are produced whenthe proton
collides with a nucleus of the material in the device. Some single event effects
are non-destructive as in the case of single event upsets (SEUs), single event
transients (SETs), multiple bit errors(MBEs), single event hard errors (SHEs),
etc. Single event effects can also be destructive as in the case ofsingle event
latchups (SELs), single event gate ruptures (SEGRs), and single event burnouts
(SEBs). Theseverity of the effect can range from noisy data to loss of the
mission, depending on the type of effect andthe criticality of the system in
which it occurs. Shielding is not an effective mitigator for single eventeffects
because they are induced by very penetrating high energy particles. The
preferred method fordealing with destructive failures is to use SEE-hard parts.
When SEE-hard parts are not available, latchupprotection circuitry is sometimes
used in conjunction with failure mode analysis. For non-destructiveeffects,
mitigation takes the form of error-detection and correction codes (EDACs),
filtering circuitry, etc.Total ionizing dose is primarily caused by protons and
electrons trapped in the Van Allen belts and solarevent protons. As electrons
are slowed down, their interactions with orbital electrons of the
shieldingmaterial produce a secondary photon radiation known as bremsstrahlung.
Generally, the dose due togalactic cosmic ray ions and proton secondaries is
negligible in the presence of the other sources. Forsurface degradation, it is
also important to include the effects of very low energy particles.Single event
effects can be induced by heavy ions (solar events and galactic cosmic rays)
and, in somedevices, protons (trapped and solar events) and neutrons.
Displacement damage is primarily due to trappedand solar protons and also
neutrons that are produced by interactions of primary particles with
theatmosphere and spacecraft materials.Spacecraft charging can occur on the
surface of the spacecraft due tolow energy electrons. Deep dielectric charging
occurs when high energy electrons penetrate the spacecraftand collect in
dielectric materials.IV. The NGST MissionThe NGST spacecraft will be transferred
out to the L2 point via a trajectory that has not yet been defined.While in the
transfer, NGST will pass through the trapped proton and electron belts. These
exposurescould constitute a single event effect risk during some maneuvers but
will not contribute to significantdegradation effects. During the transfer
trajectory, NGST will also encounter varying levels of
galactic______________________In avionics applications it is necessary to
consider neutrons that are produced by interactions of primary particles withthe
atmosphere.
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5cosmic ray heavy ions and possibly protons and heavier ions from solar events.
It will also be necessary totake the charging effects of the trapped electrons
into account.Once NGST is at L2, its mission requirement is 5 years, and its
mission goal is 10 years. With its expectedJune 2009 launch date, the NGST
mission will occur during the active phase of the solar cycle. During theactive
phase of the sun, the likelihood that the spacecraft will be exposed to
particles from solar events(either solar flare of coronal mass ejections)
increases significantly. Based on an average 11-year solarcycle, the NGST
mission will encounter 5 years of solar active conditions. The 10 years extended
missionwill encounter 7 years of solar active conditions. Figure 1shows a
projection of the solar cycle during theNGST mission, it is based on the solar
activity data of solar cycles 22 and 23. The L2 radiationenvironment encountered
by the NGST will consist of protons and heavier ions from solar events,
galacticcosmic ray heavy ions, and solar wind plasma consisting of low energy
protons, electrons, and heavier
ions.020406080100120140160180200920102011201220132014201520162017201820192020yearsunspot
number (projection from cycles 22 &23)Figure 1 : projection of the solar
activity during the NGST missionV. Total Dose and DegradationThe total ionizing
dose accumulation causes performance degradation and failure on memories,
powerconverters, etc. Non-ionizing energy loss in materials (atomic displacement
damage) causes degradation ofsolar cells, optoelectronics, and detectors. The
low energy particles also contribute to the erosion ofsurfaces.
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6A. Degradation EnvironmentAt L2 low energy particles from the solar wind plasma
contribute to the degradation of surface materials.The higher energy particles
trapped in the Van Allen belts and from high energy solar events can
penetratesolar cell coverglasses and solar array substrate structures and,
therefore, are responsible for solar celldegradation.1. The Plasma
EnvironmentThe solar wind is composed of protons and heavier ions (roughly 95%
and H+and 5% H++ ) combined withenough electrons to form an electrically neutral
plasma. It is commonly described in terms of averagedensity, velocity, and
temperature. Table 1lists average values or a range of values for these
parametersTable 1Average Solar Wind ParametersDensity1-10
particles/cm3Velocity400 km/sEnergy"a few eV"A model of the solar wind plasma
that can be used for engineering applications such as materialdegradation
analysis and spacecraft surface charging is not available at this time. However,
a joint effort atGSFC and MFSC is underway to develop a plasma model for these
applications. In the meantime, recentsatellite measurements provide a good
understanding of the dynamic range of the density, velocity, andenergy
temperature.The plasma environment for the NGST spacecraft will depend on its
position relative to the magnetotailregion of the earth's magnetosphere.*The
data given here from the GEOTAIL and SOHO spacecraft give asampling of the
expected range of the solar wind parameters inside and outside of the
magnetotail. TheSOHO spacecraft has also measured plasma parameters with the
Mass Time-of-Flight/Proton Monitor.Measurements [3] are given here outside of
the tail region at ~230 earth radii during January 1997.Figures 2-4plot the
plasma density, velocity, and energy. A sampling of the data is given in Table
2. Thedata in the table and figures show that the average solar wind parameters
given in Table 1 comparefavorably with the SOHO
measurements.______________________*The magnetotail of the magnetosphere is
formed by the interactions of the solar wind with the Earth's magnetic field.In
the solar direction, the magnetic field lines are compressed down to ~12 earth
radii under average solar-magneticconditions. In the anti-solar direction, the
solar wind "stretches" the magnetic field lines out to hundreds of earth
radii,forming the magnetotail.
Page 7
7Table 2SOHO CELIAS Proton Monitor Outside Magnetotail ~ 230-250 ReSubstorm
ConditionsDayHourDensity (#/cm3)Energy (eV)Bulk Speed
(km/s)11223.46.842511318.57.544111413.114.748711518.115.248911614.717.6500Relaxed
Substorm Conditions (medium density/low bulk velocity)DayHourDensity
(#/cm3)Energy (eV)Bulk Speed
(km/s)1638.61.93041648.12.13131655.82.33191663.22.83401673.23.0331Relaxed
Substorm Conditions (low density/high velocity)DayHourDensity (#/cm3)Energy
(eV)Bulk Speed
(km/s)28233.214.76172902.714.76102912.514.76022922.314.76092932.614.7612Measurements
from the GEOTAIL [4] spacecraft's Comprehensive Plasma Instrument Hot
PlasmaAnalyzer (CPI-HP) were used to determine the dynamic range of the solar
wind in the magnetotail region.Figure 5shows a segment of the orbit path or the
GEOTAIL spacecraft as a function of distance from theEarth in units of earth
radii. The trajectory is labeled with Julian days of the year. Note that,
atapproximately Julian day 310 (in November 1993), the spacecraft was in the
magnetotail region at ~200earth radii. At that time, a series of substorms
occurred in the tail region. Thus, this sampling should givea good measure of
the solar wind parameters to be expected during extreme conditions. Figures
6-8plotthe plasma density, velocity, and temperature for a 24 hour period during
the substorm. A sampling of thedata for that time period is given in Table 3.
The ion composition is roughly 95%H+and 5% H++.
Page 8
8Table 3GEOTAIL Comprehensive Plasma Instrument Hot Plasma AnalyzerMagnetotail
Plasma at ~210 Re During Substorm Conditions, November 18, 1993High Density/Low
Bulk Velocity and Thermal EnergyHourMinSDensity (#/cm3)Energy (eV)Bulk Speed
(km/s)35012.1727.717.8261.735116.1728.420.6258.135220.1727.515.7256.035324.1738.111.7256.135428.1745.29.4249.235532.1731.213.6251.335636.1731.711.5256.735740.1728.214.2260.435844.1721.122.3261.235948.1726.716.4256.14052.1739.711.0253.0Low
Density/High Bulk Velocity and Thermal EnergyHourMinSDensity (#/cm3)Energy
(eV)Bulk Speed
(km/s)52612.170.1562.3307.352716.170.21043.9331.352820.170.2724.9276.852924.170.21011.3193.153028.170.11499.4175.253132.170.11167.0349.853236.170.11047.4519.553340.170.2642.5360.553444.170.1848.7369.83548.170.1824.7534.753652.170.11333.9258.2A
comparison of the SOHO and GEOTAIL measurements for the solar wind shows that
the plasma densityin the magnetotail can increase to over 100 particles/cm3for
short periods of time (Figures 4 and 6).Comparing Figures 2 and 8, it can be
seen that the energy of the plasma can increase in the magnetotailfrom a "few
eV" to the keV level. For these samplings, the general description of the
velocity as 400 km/sis accurate; however, Figure 6 shows that the solar wind
velocity has a large range within a 24-hour periodand that the changes are
extremely rapid.
Page 9
9Figure 2: A sampling of the solar wind energy as measured by the SOHO
spacecraft.Figure 3: A sampling of the solar wind velocity as measured by the
SOHO spacecraft.SOHO PROTON MONITOR, SOLAR WIND ENERGY, JANUARY 5-30,
199711010010001000051015202530Day of January 1997Energy (eV)Probable Thermal
Energy H+SOHO PROTON MONITOR BULK VELOCITY H+ JANUARY 5-30,
1997010020030040050060070080051015202530Day of January 1997Velocity (km/s)Bulk
Velocity H+
Page 10
10Figure 4: A sampling of the solar wind density as measured by the SOHO
spacecraft.Figure 5: Position of GEOTAIL in the magnetotail.SOHO PROTON MONITOR,
H+ DENSITY, JANUARY 5-30, 19970.010.1110100100051015202530Day of January
1997Density (particles/cm3)H+ Density
Page 11
11Figure 6: A sampling of the ion density as sampled by GEOTAIL.Figure 7: A
sampling of ion bulk velocity by GEOTAIL.GEOTAIL CPI-HP, Ion Density
(Particles/cc), November 18, 19930.010.111010010000123456789 10 11 12 13 14 15
16 17 18 19 20 21 22 23 24UT (Hour)Density (particles/cm3)Ion DensityGEOTAIL
CPI-HP, Ion Bulk Velocity (km/s), November 18, 1993
01002003004005006007008000123456789 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24UT (Hour)Velocity (km/s)
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12Figure 8: A sampling of ion energy by GEOTAIL.2. High Energy Particles
Spacecraft Incident FluencesThe spacecraft incident proton fluence levels given
in this document are most often used for standard solarcell analyses that take
into account the coverglass thickness of the cell. There are three possible
sources ofhigh energy particles: trapped protons and trapped electrons
encountered in the transfer trajectory andprotons from solar events that can
occur anytime during the five to seven solar active years of the mission.The
trapped particles encountered in the transfer trajectory cannot be evaluated at
this time but are usuallynot a factor in degradation analyses. The proton
fluence levels are also used to determine displacementdamage effects, however,
most analysis methods require that the surface incident particles be
transportedthrough the materials surrounding the sensitive components. The
proton fluences behind nominalaluminum shield thicknesses are given in Section
V.A.3.When the transfer trajectory is known, the trapped particle fluxes will be
estimated with NASA's AP-8 [5]model for protons and AE-8 [6] model for
electrons. The models come in solar minimum and maximumversions. The uncertainty
factors defined for the models are a factor of 2 for the AP-8 and 2 to 5 for
theAE-8. These uncertainty factors apply to long term averages expected over a 6
month mission duration.Daily values can fluctuate by two to three orders of
magnitude depending on the level of activity on the sunand within the
magnetosphere.The solar proton levels can now be estimated from the new Emission
of Solar Proton (ESP) model [7].Previously, estimates of solar proton levels
were obtained from models [8,9] that were largely empirical innature, making it
difficult to add data to the model from more recent solar cycles. The ESP model
is basedon satellite data from solar cycles 20, 21, and 22. The distribution of
the fluences for the events is obtainedfrom maximum entropy theory, and design
limits in the worst case models are obtained from extreme valuetheory.GEOTAIL
CPI-HP, Ion Energy at 210 Earth Radii in Magnetotail, Nov. 18,
19931101001000100000123456789 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24UT
(Hour)Energy (eV)Ion (95% H+, 5% He++)
Page 13
13Total integral solar proton fluences were estimated for 1, 5, and 7 solar
active years with 5 years being thenumber of years to consider for the nominal
mission and 7 years the number of years to consider for the 10years extended
mission. Tables A1-A3give the fluence levels as a function of particle energy
for 80, 85,90, 95, and 99% confidence levels. Figures 9-11are plots of the
energy-fluences spectra for 1, 5, and 7solar active years for the given
confidence levels. In addition, Figure 12compares the 1, 5, and 7 yearsolar
proton fluence levels for the 95% confidence level. The energies are in units of
>MeV and thefluences are in units of particles/cm2. These values do not include
a design margin. The solar protonpredictions are not linear over time;
therefore, these estimates may be invalid if extrapolated for longermission
durations.Solar Proton Fluence for Various Confidence Levels 1 Solar Active
Year1.00E+061.00E+071.00E+081.00E+091.00E+101.00E+111.00E+12050100150200250300350Energy
(> MeV)Proton Fluence (#/cm2- 1 solar active year)80%85%90%95%99%Figure 9: Solar
proton fluences for 1 solar active year are presented for various confidence
levels.
Page 14
14Solar Proton Fluence for Various Confidence Levels 5 Solar Active
Years1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+121.00E+13050100150200250300350Energy
(> MeV)Proton Fluence (#/cm2-5 solar active years)80%85%90%95%99%Figure 10:
Solar proton fluences for 5 solar active years are presented for various
confidence levels.Solar Proton Fluence for Various Confidence Levels7 Solar
Active
Years1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+121.00E+13050100150200250300350Energy
(>MeV)Proton Fluence (#/cm2 - 7 solar active years)80%85%90%95%99%Figure 11:
Solar proton fluences for 7 solar active years are presented for various
confidence levels.
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15Solar Proton Fluence for 1,5 and 7 Solar Active years 95% Confidence
Level1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+121.00E+13050100150200250300350Energy
(> MeV)Proton Fluence (#/cm2)5 Solar Active Years7 Solar Active Years1 Solar
Active YearFigure 12: Solar proton fluences for a 95% confidence level are
presented for 1, 5, and 7 solar active years.3. High Energy Particles Shielded
FluencesEvaluation of non-ionizing energy loss damage requires the use of
shielded fluence levels. For this analysisnominal shielding thicknesses of 50,
100, 200, and 500 mils of aluminum were used for a generic solidsphere geometry.
The spacecraft incident, solar proton estimates for the 95% confidence level and
for 1, 5,and 7 year solar active years were transported through the shield
thickness to obtain fluence estimatesbehind the shielding. Tables A4-A6give the
degraded energy spectra. The spectra are plotted inFigures 13-15. Figure 16shows
a comparison for 1, 5, and 7 solar active years for 100 mil shielding case.It
can be seen from the figures that even though low energy particles are absorbed
by the shielding, the lowenergy range of the spectrum is filled in by the higher
energy protons as they are degraded by passingthrough the material.
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16Shielded integral Solar Proton Fluence for 1 Solar Active Year 95% Confidence
Level - Values do not include Design
Margins1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+120.11101001000Energy (>
MeV)Protons (#/cm2- 1 Solar Active Year)Spacecraft incident50 mils Al (1.27
mm)100 mils Al (2.54 mm)200 mils Al (5.08 mm)500 mils Al (12.7 mm)Figure 13:
Shielded solar proton energy spectra for 1 solar active year, 95% confidence
level.Shielded integral Solar Proton Fluences for 5 Solar Active Years 95%
Confidence Level - Values do not include Design
Margins1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+121.00E+130.11101001000Energy
(>MeV)Protons(#/cm2-5 Solar Active years)Spacecraft Incident50 mils Al (1.27
mm)100 mils Al (2.54 mm)200 mils Al (5.08 mm)500 mils Al (12.7 mm)Figure 14:
Shielded solar proton energy spectra for 5 solar active years, 95% confidence
level.
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17Shielded Integral Solar Proton Fluences for 7 Solar Active years 95%
Confidence Level - Values do not include Design
Margins1.00E+071.00E+081.00E+091.00E+101.00E+111.00E+121.00E+130.11101001000Energy
(> MeV)Protons (#/cm2 - 7 solar active years)Spacecraft incident50 mils Al (1.27
mm)100 mils Al (2.54 mm)200 mils Al (5.08 mm)500 mils Al (12.7 mm)Figure 15:
Shielded solar proton energy spectra for 7 solar active years, 95% confidence
level.Shielded Integral Solar Proton Fluences for 100 mils (2.54mm) Aluminum 95%
Confidence Level - Value do not include Design
Margins1.00E+071.00E+081.00E+091.00E+101.00E+110.11.010.0100.01000.0Energy (>
MeV)Protons (#/cm2)1 Solar Active Year5 Solar Active Years7 Solar Active
YearsFigure 16: Shielded solar proton energy spectra for 100 mils aluminum 95%
confidence level
Page 18
18B. Total Dose Estimates1. Top Level Ionizing Dose RequirementDoses are
calculated from the surface incident integral fluences as a function of aluminum
shield thicknessfor a simple geometry. The geometry model used for spacecraft
applications is the solid sphere. The solidsphere doses represent an upper
boundary for the dose inside an actual spacecraft and are used as a top-level
requirement. In cases where the amount of shielding surrounding a sensitive
location is difficult toestimate, a more detailed analysis of the geometry of
the spacecraft structure may be necessary to evaluatethe expected dose levels.
This is done by modeling the electronic boxes or instruments and the
spacecraftstructure. The amount of shielding surrounding selected sensitive
locations is estimated using solid anglesectoring and 3-dimensional ray tracing.
Doses obtained by sectoring methods must be verified for 5-10%of the sensitive
locations with full Monte Carlo simulations of particle trajectories through the
structure formany histories.Table A7and Figures 17 and18give the top-level total
ionizing dose requirement for the 5 year NGSTmission and for the 10 year
extended mission. The doses are given for 1, 5, and 7 solar active years for
a95% confidence level. The best estimate at this time predicts 5 solar active
years for the nominal missionand 7 solar active years for the extended mission
given the 2009 NGST launch. The doses are calculatedhere as a function of
aluminum shield thickness in units of krads in silicon. For the nominal 100 mils
ofequivalent aluminum shielding and the 5 years nominal mission , the dose
requirement is 18 krad-Si withno design margin. For the nominal 100 mils of
equivalent aluminum shielding and the 10 years extendedmission , the dose
requirement is 24 krad-Si with no design margin A minimum design margin of x 2
isrecommended.
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19Total Dose at the Center of Solid Aluminum Spheres- Top Level Requirement95%
Confidence Level - Values do not include Design
Margin0.010.101.0010.00100.001000.000500100015002000250030003500400045005000Aluminum
Shield Thickness (mils)Dose (krad-Si)1 Solar Active Year5 Solar Active Years7
Solar Active yearsFigure 17: Total ionizing dose from solar proton events for 1,
5, and 7 solar active years is presented.Total Dose at the Center of Solid
Aluminum Spheres- Top Level Requirement95% Confidence Level - Values do not
include Design
Margin0.010.101.0010.00100.001000.0001002003004005006007008009001000Aluminum
Shield Thickness (mils)Dose (krad-Si)1 Solar Active Year5 Solar Active Years7
Solar Active yearsFigure 18: Total ionizing dose from solar proton events for 1,
5, and 7 solar active years is presented.
Page 20
202. Dose at Specific Spacecraft LocationsIn cases where parts cannot meet the
top level design requirement and a "harder" part cannot be substituted,it is
often beneficial to employ more accurate methods of determining the dose
exposure for somespacecraft components to qualify the parts. One such method for
calculating total dose, solid anglesectoring/3-dimensional ray tracing, is
accomplished in three steps:1) Model the spacecraft structure:-develop a 3-D
model of the spacecraft structures and components-develop a material
library-define sensitive locations2) Model the radiation environment:-define the
spacecraft incident radiation environment-develop a particle attenuation model
using theoretical shielding configurations(similar to dose-depth curves).3)
Obtain results for each sensitive location:-divide the structural model into
solid angle sectors-ray trace through the sectors to calculate the material mass
distribution-use the ray trace results to calculate total doses from the
particle attenuation model.Once the basic structural model has been defined,
total doses can be obtained for any location in thespacecraft in a short time
(in comparison to Monte Carlo methods). The value of dose mitigation measurescan
be accurately evaluated be adding the changes to the model and recalculating the
total dose. Forspacecraft with strict weight budgets, the 3-D ray trace method,
the total dose design requirement can bedefined at a box or instrument level
avoiding unnecessary use of expensive or increasingly unavailableradiation
hardened parts.As the design of the NGST evolves, it may become necessary to
estimate the doses at specific locations inthe spacecraft or instruments. Often
the dose requirement can be met by modeling the surroundingelectronic box only
or by modeling only the instrument.C. Displacement Damage EstimatesTotal
non-ionizing energy loss damage is evaluated by combining the shielded proton
energy spectra givenSection V.A.3 with the NIEL Non Ionizing Energy Loss (NIEL)
response curves for the material and theresults of laboratory radiation of the
devices sensitive to atomic displacement damage. The level of thehazard is
highly dependent on the device type and can be process specific. For the NGST
mission, it isimportant to keep in mind that some optoelectronic devices
experience enough damage during one largesolar proton event to cause the device
to fail. It is necessary that the parts list screening for radiation alsoinclude
a check for devices that are susceptible to displacement damage.
Page 21
21VI. Single Event Effects AnalysisA. Heavy Ion Induced Single Event EffectsSome
electronic devices are susceptible to single event effects (SEEs), e.g., single
event upsets, singleevent latch-up, single event burn-out. Because of their
ability to penetrate to the sensitive regions ofdevices and their ability to
ionize materials, heavy ions cause SEEs by the direct deposit of charge.
Thequantity most frequently used to measure an ion's ability to deposit charge
in devices is linear energytransfer (LET). Heavy ion abundances are converted to
total LET spectra. Once specific parts are selectedfor the mission and, if
necessary, characterized by laboratory testing, the LET spectra for the heavy
ions areintegrated with the device characterization to calculate SEE rates.
Heavy ion populations that havesufficient numbers to be a SEE hazard are the
galactic cosmic rays and those from solar events.1. Galactic Cosmic RaysThe
cosmic ray fluxes for elements hydrogen through uranium were used to calculate
daily LET spectra for100 mils nominal aluminum shielding as given in Table A8and
Figure 19. The range of the cosmic rayabundances is bounded by the extremea of
the solar active and inactive phases of the solar cycle with thehighest values
occurring during the solar inactive phase and the lowest during the solar active
phase. Withthe extended mission goal of 10 years, the highest values should be
used for single event effects analyses.The LET fluence values are given for the
highest and lowest point of the solar cycle. The new CREME96[10] model was used
to obtain the cosmic ray heavy ion abundances. This model has an accuracy of
25-40%.Integral LET Spectra at 1AU (Z=1-92) for Interplanetary Galactic Cosmic
Rays 100 mils Aluminum Shielding,
CREME961.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+001.00E+011.00E+021.00E+031.00E+041.00E+051.00E+061.E-031.E-021.E-011.E+001.E+011.E+021.E+03LET
energy (MeV-cm2/mg)LET fluence (#/cm2-day)Solar minimumSolar maximumFigure 19:
Integral LET spectra are shown for galactic cosmic ray ions hydrogen through
uranium.
Page 22
222. Solar Heavy IonsThe heavy ions from solar flares and coronal mass ejections
can also produce single event effects. Thesolar event fluxes for the elements
hydrogen through uranium were used to calculate daily LET spectra for100 mils
nominal aluminum shielding in units of average LET flux per second. The
intensity of the fluxesvaries over the duration of an event; therefore, values
are averaged over the worst week of the solar cycle,the worst day of the solar
cycle, and the peak of the October 1989 solar event. Table A9and Figure 20give
the solar heavy ion LET predictions for the NGST mission. The new CREME96 model
was also usedto calculate the solar heavy ion levels. An uncertainty factor for
the solar heavy ion model has not beenreleased.Integral LET Spectra at 1 AU
(Z=1-92) for Interplanetary Solar Particle Events 100 mils Aluminum Shielding,
CREME961.00E-111.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+001.00E+011.00E+021.00E+031.00E+041.00E+051.00E+061.00E-031.00E-021.00E-011.00E+001.00E+011.00E+021.00E+03LET
Energy (MeV-cm2/mg)LET Fluence (#/cm2-s)Average Over PeakAverage Over Worst
DayAverage Over Worst WeekFigure 20: Integral LET spectra are shown for hydrogen
through uranium for the October 1989 solar particle event.B. Proton Induced
Single Event EffectsIn some devices, single event effects are also induced by
protons. Protons from the trapped radiation beltsand from solar events do not
generate sufficient ionization (LET < 1 MeV-cm2 /mg) to produce the
criticalcharge necessary for SEEs to occur in most electronics. More typically,
protons cause Single Event Effectsthrough secondary particles via nuclear
interactions, that is, spallation and fractionation products. Becausethe proton
energy is important in the production (and not the LET) of the secondary
particles that cause theSEEs, device sensitivity to these particles is typically
expressed as a function of proton energy rather thanLET.
Page 23
231. Trapped ProtonsTrapped protons can be a concern for single event effects
during the transfer trajectory passes through thetrapped particle radiation
belts. The proton fluxes in the intense regions of the belts reach levels that
arehigh enough to induce upsets or latchups. The timing of critical operations
during the transfer trajectoryshould be analyzed to determine the trapped proton
environment at the time of the operation.2. Solar ProtonsProtons from solar
events can also be a single event effects hazard for the NGST spacecraft.
Theseenhanced levels of protons could occur anytime during the 5 to 10 year
mission but are most likely duringthe portion of the mission that occurs during
the active phase of the solar cycle. As with the solar heavyion LET, solar
proton fluxes are averaged over worst day, worst week, and the peak of the
October 1989solar event. The proton flux averages for a nominal 100 mils of
shielding are given in Table A10 and areshown in Figure 21.1 .0 E-031 .0 E-021
.0 E-011.0E+001.0E+011.0E+021.0E+031.0E+041.0E+0511 01 0 01000E n e r g y ( M e
V )Particles (#/cm2/s/MeV)A v e r a g e O ve r P e a kA v e r a g e O ve r Worst
DayA v e r a g e O ve r Worst W e e kV a l u e s D o N o t Include Design
MarginD ifferential Solar Proton Event Fluxes at 1 AU100 m ils A luminum S hie
lding, CREME96Figure 21: Solar proton fluxes for single event effects
evaluation.VII. Instrument InterferenceFor NGST the particle background is also
a concern for instrument observations. To estimate the nominalparticle
background level, the energy spectra for galactic cosmic ray heavy ion elements
were estimatedwith the CREME96 model and summed. Fifty mils of aluminum
shielding was assumed. The result isshown in Figure 22. Note that the hydrogen
component dominates the total number of ions. The total ionflux was integrated
over energy to obtain a background count of 5 ions/cm2/s.
Page 24
24Total D ifferential Ion Flux - GCR BackgroundShielded - 50 mils Al, CREME96
(Z=1-92)1.0E-081.0E-071.0E-061.0E-051.0E-041.0E-031.0E-020.1110100100 01000
0100000Energy (MeV/n)Ions (#/cm2/s/MeV/n))Total GCRH GCRIntegrated Over Energy =
5 ions/cm2/sFigure 22: Total differential fluence for all galactic cosmic ray
particles for a 1 second time period.Particle interference during solar events
is of particular concern because it can impact the observation timesof the
instruments. To obtain an estimate for the peak particle count, the total number
of particles wasestimated from the solar heavy ion model of the CREME96 code
which is based on the October 1989 solarparticle event. The particles were
summed and integrated using the same method as with the galacticcosmic ray
background. It was estimated the particle rate is approximately 2.5 x
105ions/cm2/s. Theresults are shown in Figure 23.Total Differential Ion Flux -
Averaged 5-Min Peak during Solar EventShielded - 50 mils Al, CREME96 (Z=1-92)1
.0E-1 01 .0E-0 91 .0E-0 81 .0E-0 71 .0E-0 61 .0E-0 51 .0E-0 41 .0E-0 31 .0E-0 21
.0E-0 11.0E+001.0E+011.0E+021.0E+031.0E+041.0E+050.111 0100100010000100000Energy
(MeV/n)Ions (#/cm2/s/MeV/n))Total SolarIntegrated Over Energy = 2.5 x
105ions/cm2/sFigure 23: Total differential fluence of all predicted solar
particles based on the October 1989 event
Page 25
25It is necessary to have a clearer understanding of how the solar particle
events impact viewing and datacollection activities on the NGST. Therefore,
solar proton flux data were obtained from the SpaceEnvironment Monitor (SEM)
Mission of the Geosynchronous Operational Environmental Satellites(GOES) [11].
The 5 minute average data were extracted from the GOES SEM data base*and
converted tointegral flux in particles/cm2/s/steradian for proton flux levels
greater than 1, 5, 10, 30, 50, 60 and 100MeV, for the years 1986 through 1996.
These data were converted to hourly averages in order to reducethe size of the
data set.The distribution of solar proton flux for particles with energies
greater than 30 and 50 MeV were firstanalyzed. The distribution is measured by
counting the number of hours the average flux was greater than1, 2, 5, 10, 20,
or 50 particles/cm2/s for each year, and converting hours to days for
presentation purposes.The results are shown in Figures 24
and25.0204060801001201401601802001986 1987 1988 1989 1990 1991 1992 1993 1994
1995 1996Cumulative Distribution of Solar Proton Flux > 30MeVFlux > 1
part/cm^2/secFlux > 2 part/cm^2/secFlux > 5 part/cm^2/secFlux > 10
part/cm^2/secFlux > 20 part/cm^2/secFlux > 50 part/cm^2/secDays of
YearYearFigure 24: The cumulative distribution of > 30 MeV solar protons for the
last solar cycle.0204060801001201401601986 1987 1988 1989 1990 1991 1992 1993
1994 1995 1996Cumulative Distribution of Solar Proton Flux > 50MeVFlux > 1
part/cm^2/secFlux > 2 part/cm^2/secFlux > 5 part/cm^2/secFlux > 10
part/cm^2/secFlux > 20 part/cm^2/secFlux > 50 part/cm^2/secDays of
YearYearFigure 25: The cumulative distribution of > 50 MeV solar protons for the
last solar cycle______________________*The authors wish to thank Paul McNulty
and Craig Stauffer of SGT, Inc., Greenbelt, MD for their support inextracting
the GOES data.
Page 26
26These figures clearly show the impact of most active periods of the solar
maximum phase solar cycle 22,which occurred during the years 1989-1992. If solar
cycle 24 has a period of 11 years and its activity issimilar to solar cycle 22,
the peak of the solar particle activity will occur during the years
2011-2014following NGST launch around 2009.Extreme flux levels will raise the
concern of single event upsets interfering with operation of the vehicle
orposing a health and safety hazard. To establish reasonable worst case
scenarios for the solar radiationenvironment, the next analysis focused on the
years 1989-1991. Figures 26-28show the hourly averagesolar proton flux for
particles greater than 50 MeV for each of the years 1989-1991. Note that the
scale forflux is logarithmic, and the flux variation is
significant.100101102103104105050100150200250300350Hourly Average of Solar
Proton Flux > 50 MeV for 1989Flux (>50MeV Particles/cm^2/sec)Day of YearGOES
Space Environment Monitor DataFigure 26: Hourly averages of solar proton fluxes
for > 50 MeV protons for 1989.100101102103104105050100150200250300350Hourly
Average of Solar Proton Flux > 50 MeV for 1990Flux (>50MeV
Particles/cm^2/sec)Day of YearGOES Space Environment Monitor DataFigure 27:
Hourly averages of solar proton fluxes for > 50 MeV protons for 1990.
Page 27
27100101102103104105050100150200250300350Hourly Average of Solar Proton Flux >
50 MeV for 1991Flux (>50MeV Particles/cm^2/sec)Day of YearGOES Space Environment
Monitor DataFigure 28: Hourly averages of solar proton fluxes for > 50 MeV
protons for 1991.Moderate flux levels will affect the ability of NGST to observe
dim targets with long exposures. Thegalactic background flux is 5
particles/cm2/s at L2, so NGST will be configured to operate in thisenvironment.
To address the problem of observation interference during solar particle events,
thedistributions of the solar proton flux counts for 1989, 1990, and 1991 were
estimated. During these solarmaximum years, the solar proton flux will vary
significantly and will increase the total flux by severalparticles for a large
portion of the year. Figures 29and 30show the cumulative distributions of
solarproton flux for particles greater than 30 and 50 MeV for 1989, 1990, and
1991, and the average of theseyears.. These figures show that, for an average of
almost two months for each year of solar maximum, thesolar proton flux will
exceed 5 particles/cm2/s for > 30 MeV protons (or over one month per year for >
50MeV protons).01020304050600153045607590Cumulative Distribution of Solar Proton
Flux > 30 MeVfor Peak Solar Cycle Years 1989-19911989 Flux 1990 Flux 1991 Flux
Avg. Flux0153045607590Flux (>50 MeV particles/cm^2/sec)Days of YearGOES Space
Environment Monitor DataFigure 29: Distribution of solar proton flux counts at >
30 MeV
Page 28
28051015200153045607590Cumulative Distribution of Solar Proton Flux > 50 MeVfor
Peak Solar Cycle Years 1989-19911989 Flux 1990 Flux 1991 Flux Avg.
Flux0153045607590Flux (>50 MeV particles/cm^2/sec)Days of YearGOES Space
Environment Monitor DataFigure 30: Distribution of solar proton flux counts at >
50 MeV.VIII. Spacecraft Charging and DischargingSurface charging and deep
dielectric charging must also be evaluated for the NGST mission. Both
arepotentially a problem in transfer trajectories that take long loops through
the Van Allen belts. During theseloops, the spacecraft can accumulate high
levels of electron build-up on spacecraft surfaces (low energyelectrons) in the
dielectrics (high energy electrons). When the transfer trajectory of NGST is
known inmore detail, the particle accumulation profiles must be estimated and
analyzed for possible surface anddeep dielectric charging effects.At L2 there is
also concern that surface charges can build up due to the differential in the
plasma during thepasses in and out of the magnetotail. This analysis should be
performed when the plasma model becomesavailable.IX. SummaryA top-level
radiation environment specification was presented for the NGST mission. Although
theenvironment is considered "moderate", the environment poses challenges to
mission designers because ofits highly variable nature caused by activity on the
sun.Spacecraft and instrument designers must be made aware that some newer
technologies and commercial-off-the-shelf (COTS) devices are very soft to
radiation effects. COTS devices that lose functionality at5 krads of dose are
not uncommon. One extremely large solar proton event can cause enough
displacementdamage degradation in some optocoupler devices to cause failure.
Increasingly, single event effects requirecareful part selection and mitigation
schemes. With its full exposure to galactic cosmic heavy ions andparticles from
solar events, NGST must have a carefully planned radiation engineering program.
Page 29
29X. References[1]A. Holmes-Siedle and L. Adams, Handbook of Radiation Effects,
p. 16, Oxford University Press,Oxford, 1993.[2]A. R. Frederickson, "Upsets
Related to Spacecraft Charging," IEEE Trans. on Nucl. Science, Vol.43, No. 2,
pp. 426-441, April 1996.[3]F.M. Ipavich et al., (in press JGR 1997), Space
Physics Group, University of Maryland, "TheSolar Wind Proton Monitor on the SOHO
Spacecraft," [WWW Dosument], URLhttp://umtof.umd.edu/papers/pml.htm[4]L. A.
Frank, et al., "The Comprehensive Plasma Instrumentation (CPI) for the
GEOTAILSpacecraft," J. Geomag. Geoelec., Vol. 46, pp. 23-37, 1994.[5]D. M.
Sawyer and J. I. Vette, "AP-8 Trapped Proton Environment," NSSDC/WDC-A-R&S
76-06,NASA/Goddard Space Flight Center, Greenbelt, MD, December 1991.[6]J. I.
Vette, "The AE-8 Trapped Electron Model Environment," NSSDC/WDC-A-R&S
91-24,NASA/Goddard Space Flight Center, Greenbelt, MD, November 1991.[7]M. A.
Xapsos, J. L. Barth, E. G. Stassinopoulos, G. P. Summers, E.A. Burke, G. B. Gee,
"Modelfor Prediction of Solar Proton Events", to be published in Proceedings of
the 1999 SpaceEnvironment and Effects Workshop, Farnborough, UK.[8]E. G.
Stassinopoulos, "SOLPRO: A Computer Code to Calculate Probabilistic Energetic
SolarFlare Protons," NSSDC 74-11, NASA/Goddard Space Flight Center, Greenbelt,
MD, April 1975.[9]J. Feynman, T. P. Armstrong, L. Dao-Gibner, and S. Silverman,
"New Interplanetary ProtonFluence Model," J. Spacecraft, Vol. 27 No. 24, pp
403-410, July-August 1990.[10]A. J. Tylka, J. H. Adams, Jr., P. R. Boberg, W. F.
Dietrich, E.O. Flueckiger, E.L. Petersen, M.A.Shea, D.F. Smart, and E.C. Smith,
"CREME96: A Revision of the Cosmic Ray Effects on Micro-Electronics Code: to be
published in IEEE Trans. On Nuc. Sci., December 1997.[11]GOES home page -
http://julius.ngdc.noaa.gov:8080/production/html/GOES/index.html
Page 30
A-1AppendicesTable A1Spacecraft Incident Solar Proton Fluences for 1 Solar
Active YearsValues Do Not Include Design MarginsEnergyConfidence
Level(>MeV)80%85%90%95%99%11.19E+111.47E+111.91E+112.81E+115.83E+1134.18E+105.17E+106.76E+101.01E+112.12E+1152.41E+103.05E+104.08E+106.30E+101.42E+1171.68E+102.16E+102.96E+104.73E+101.14E+11109.84E+091.33E+101.95E+103.44E+109.94E+10155.61E+097.69E+091.14E+102.06E+106.20E+10203.55E+094.93E+097.44E+091.37E+104.31E+10252.43E+093.43E+095.28E+091.00E+103.34E+10301.75E+092.52E+093.97E+097.79E+092.76E+10351.32E+091.93E+093.13E+096.37E+092.42E+10401.03E+091.53E+092.54E+095.36E+092.18E+10458.07E+081.22E+092.06E+094.45E+091.90E+10506.39E+089.74E+081.66E+093.65E+091.60E+10555.10E+087.82E+081.34E+092.97E+091.32E+10604.10E+086.30E+081.08E+092.40E+091.07E+10702.73E+084.19E+087.17E+081.59E+097.07E+09801.90E+082.90E+084.94E+081.09E+094.81E+09901.36E+082.09E+083.56E+087.87E+083.48E+091001.00E+081.54E+082.64E+085.87E+082.63E+091256.05E+079.28E+071.59E+083.54E+081.59E+091503.91E+076.01E+071.03E+082.29E+081.03E+091752.68E+074.11E+077.06E+071.57E+087.03E+082001.92E+072.94E+075.05E+071.12E+085.03E+082251.41E+072.17E+073.72E+078.28E+073.71E+082501.07E+071.64E+072.81E+076.26E+072.80E+082758.25E+061.27E+072.17E+074.83E+072.16E+083006.48E+069.96E+061.71E+073.80E+071.70E+08
Page 31
A-2Table A2Spacecraft Incident Solar Proton Fluences for 5 Solar Active
YearsValues Do Not Include Design MarginsEnergyConfidence
Level(>MeV)80%85%90%95%99%15.93E+116.66E+117.71E+119.58E+111.44E+1232.10E+112.37E+112.76E+113.45E+115.25E+1151.27E+111.46E+111.73E+112.23E+113.60E+1179.28E+101.08E+111.31E+111.74E+112.97E+11106.21E+107.63E+109.90E+101.45E+112.99E+11153.64E+104.54E+105.98E+108.99E+101.93E+11202.37E+103.00E+104.02E+106.20E+101.40E+11251.68E+102.16E+102.97E+104.74E+101.14E+11301.26E+101.65E+102.32E+103.86E+101.00E+11359.79E+091.32E+101.91E+103.32E+109.36E+10407.83E+091.08E+101.61E+102.92E+108.91E+10456.26E+098.76E+091.33E+102.49E+108.04E+10505.01E+097.07E+091.09E+102.07E+106.93E+10554.02E+095.71E+098.86E+091.70E+105.79E+10603.24E+094.61E+097.17E+091.38E+104.73E+10702.16E+093.06E+094.75E+099.11E+093.10E+10801.49E+092.11E+093.26E+096.23E+092.10E+10901.07E+091.52E+092.35E+094.50E+091.52E+101007.92E+081.13E+091.75E+093.38E+091.16E+101254.78E+086.79E+081.06E+092.04E+096.99E+091503.09E+084.40E+086.85E+081.32E+094.52E+091752.12E+083.01E+084.69E+089.04E+083.10E+092001.51E+082.15E+083.35E+086.47E+082.22E+092251.12E+081.59E+082.47E+084.77E+081.63E+092508.44E+071.20E+081.87E+083.60E+081.24E+092756.52E+079.27E+071.44E+082.78E+089.53E+083005.12E+077.29E+071.13E+082.19E+087.50E+08
Page 32
A-3Table A3Spacecraft Incident Solar Proton Fluences for 7 Solar Active
YearsValues Do Not Include Design MarginsEnergyConfidence
Level(>MeV)80%85%90%95%99%18.11E+118.97E+111.02E+121.23E+121.75E+1232.88E+113.20E+113.64E+114.42E+116.36E+1151.75E+111.97E+112.29E+112.86E+114.34E+1171.29E+111.47E+111.74E+112.23E+113.57E+11108.85E+101.07E+111.35E+111.90E+113.64E+11155.23E+106.37E+108.18E+101.18E+112.37E+11203.43E+104.24E+105.54E+108.22E+101.73E+11252.45E+103.09E+104.13E+106.36E+101.42E+11301.85E+102.39E+103.28E+105.24E+101.27E+11351.46E+101.93E+102.73E+104.57E+101.20E+11401.18E+101.59E+102.32E+104.06E+101.16E+11459.49E+091.30E+101.94E+103.50E+101.06E+11507.61E+091.05E+101.59E+102.93E+109.17E+10556.12E+098.53E+091.30E+102.41E+107.68E+10604.94E+096.89E+091.05E+101.96E+106.29E+10703.28E+094.57E+096.94E+091.29E+104.11E+10802.27E+093.15E+094.76E+098.79E+092.78E+10901.63E+092.27E+093.44E+096.36E+092.02E+101001.21E+091.68E+092.57E+094.79E+091.54E+101257.27E+081.02E+091.55E+092.89E+099.29E+091504.71E+086.58E+081.00E+091.87E+096.02E+091753.22E+084.50E+086.86E+081.28E+094.12E+092002.31E+083.22E+084.91E+089.15E+082.95E+092251.70E+082.37E+083.62E+086.75E+082.17E+092501.29E+081.80E+082.73E+085.10E+081.64E+092759.92E+071.39E+082.11E+083.94E+081.27E+093007.80E+071.09E+081.66E+083.10E+089.97E+08
Page 33
A-4Table A4Integral Solar Proton Fluence Levels Behind Solid Sphere Aluminum
Shields1 Active Solar Year 95% Confidence LevelValues Do Not Include Design
MarginsShielded Solar Proton FluencesDegraded Energy50 mils Al(1.27 mm) 100 mils
Al(2.54 mm) 200 mils Al(5.08 mm) 500 mils Al(12.7 mm)>
MeV#/cm2#/cm2#/cm2#/cm20.102.02E+101.13E+106.68E+092.81E+090.132.02E+101.13E+106.68E+092.81E+090.162.02E+101.13E+106.68E+092.81E+090.202.01E+101.13E+106.68E+092.81E+090.252.01E+101.13E+106.68E+092.81E+090.322.01E+101.13E+106.68E+092.81E+090.402.01E+101.13E+106.68E+092.81E+090.502.01E+101.13E+106.67E+092.81E+090.632.01E+101.13E+106.67E+092.81E+090.792.00E+101.13E+106.67E+092.81E+091.002.00E+101.13E+106.66E+092.81E+091.261.99E+101.13E+106.66E+092.81E+091.581.98E+101.12E+106.65E+092.81E+092.001.97E+101.12E+106.64E+092.80E+092.511.94E+101.11E+106.62E+092.80E+093.161.91E+101.10E+106.59E+092.79E+093.981.86E+101.09E+106.55E+092.78E+095.011.81E+101.07E+106.49E+092.76E+096.311.72E+101.04E+106.40E+092.74E+097.941.60E+101.00E+106.27E+092.70E+0910.001.46E+109.50E+096.12E+092.65E+0912.601.29E+108.86E+095.88E+092.57E+0915.801.10E+108.01E+095.56E+092.44E+0920.009.18E+097.06E+095.15E+092.28E+0925.107.40E+096.06E+094.54E+092.05E+0931.605.87E+095.01E+093.84E+091.78E+0939.804.43E+093.82E+092.97E+091.45E+0950.102.95E+092.61E+092.05E+091.10E+0963.101.69E+091.56E+091.28E+097.81E+0879.408.86E+088.54E+087.55E+085.19E+08100.004.57E+084.50E+084.28E+083.44E+08126.002.55E+082.53E+082.47E+082.11E+08158.001.33E+081.32E+081.30E+081.16E+08200.005.86E+075.84E+075.79E+075.36E+07251.001.64E+071.64E+071.64E+071.50E+07
Page 34
A-5Table A5Integral Solar Proton Fluence Levels Behind Solid Sphere Aluminum
Shields5 Active Solar Years 95% Confidence LevelValues Do Not Include Design
MarginsShielded Solar Proton FluencesDegraded Energy 50 mils Al(1.27 mm) 100
mils Al(2.54 mm) 200 mils Al(5.08 mm) 500 mils Al(12.7 mm)>
MeV#/cm2#/cm2#/cm2#/cm20.108.78E+105.21E+103.39E+101.61E+100.138.77E+105.21E+103.39E+101.61E+100.168.77E+105.21E+103.39E+101.61E+100.208.77E+105.21E+103.39E+101.61E+100.258.77E+105.21E+103.39E+101.61E+100.328.76E+105.21E+103.39E+101.61E+100.408.76E+105.21E+103.39E+101.61E+100.508.75E+105.20E+103.39E+101.61E+100.638.74E+105.20E+103.38E+101.61E+100.798.73E+105.20E+103.38E+101.61E+101.008.71E+105.19E+103.38E+101.61E+101.268.68E+105.18E+103.38E+101.61E+101.588.64E+105.17E+103.38E+101.61E+102.008.58E+105.15E+103.37E+101.61E+102.518.49E+105.13E+103.37E+101.60E+103.168.36E+105.09E+103.35E+101.60E+103.988.17E+105.03E+103.34E+101.59E+105.017.94E+104.94E+103.32E+101.58E+106.317.59E+104.84E+103.28E+101.57E+107.947.12E+104.69E+103.23E+101.55E+1010.006.52E+104.48E+103.17E+101.52E+1012.605.86E+104.23E+103.08E+101.47E+1015.805.12E+103.89E+102.95E+101.40E+1020.004.38E+103.52E+102.79E+101.31E+1025.103.68E+103.14E+102.50E+101.18E+1031.603.09E+102.72E+102.16E+101.02E+1039.802.47E+102.15E+101.70E+108.28E+0950.101.69E+101.50E+101.18E+106.29E+0963.109.69E+098.91E+097.33E+094.46E+0979.405.05E+094.88E+094.31E+092.99E+09100.002.63E+092.59E+092.47E+091.98E+09126.001.47E+091.46E+091.42E+091.21E+09158.007.63E+087.59E+087.49E+086.68E+08200.003.38E+083.37E+083.34E+083.09E+08251.009.42E+079.42E+079.42E+078.62E+07
Page 35
A-6Table A6Integral Solar Proton Fluence Levels Behind Solid Sphere Aluminum
Shields7 Active Solar Years 95% Confidence LevelValues Do Not Include Design
MarginsShielded Solar Proton FluencesDegraded Energy50 mils Al(1.27 mm) 100 mils
Al(2.54 mm) 200 mils Al(5.08 mm) 500 mils Al(12.7 mm)>
MeV#/cm2#/cm2#/cm2#/cm20.101.15E+116.93E+104.63E+102.29E+100.131.15E+116.93E+104.63E+102.29E+100.161.15E+116.93E+104.63E+102.29E+100.201.15E+116.93E+104.63E+102.29E+100.251.15E+116.93E+104.63E+102.29E+100.321.15E+116.93E+104.63E+102.29E+100.401.15E+116.93E+104.63E+102.29E+100.501.15E+116.92E+104.62E+102.29E+100.631.15E+116.92E+104.62E+102.28E+100.791.15E+116.92E+104.62E+102.28E+101.001.14E+116.91E+104.62E+102.28E+101.261.14E+116.90E+104.62E+102.28E+101.581.13E+116.88E+104.61E+102.28E+102.001.13E+116.86E+104.61E+102.28E+102.511.11E+116.83E+104.60E+102.27E+103.161.10E+116.78E+104.59E+102.27E+103.981.07E+116.70E+104.57E+102.26E+105.011.04E+116.59E+104.54E+102.25E+106.311.00E+116.45E+104.50E+102.23E+107.949.39E+106.26E+104.43E+102.20E+1010.008.62E+106.00E+104.36E+102.15E+1012.607.77E+105.68E+104.24E+102.09E+1015.806.84E+105.25E+104.08E+101.99E+1020.005.88E+104.79E+103.87E+101.86E+1025.105.00E+104.31E+103.50E+101.67E+1031.604.27E+103.78E+103.05E+101.45E+1039.803.46E+103.04E+102.41E+101.17E+1050.102.39E+102.12E+101.67E+108.88E+0963.101.37E+101.26E+101.04E+106.30E+0979.407.13E+096.88E+096.08E+094.23E+09100.003.72E+093.67E+093.50E+092.81E+09126.002.08E+092.07E+092.01E+091.72E+09158.001.08E+091.08E+091.06E+099.46E+08200.004.79E+084.77E+084.73E+084.37E+08251.001.34E+081.34E+081.34E+081.23E+08
Page 36
A-7Table A7Total Ionizing Dose at the Center of Aluminum Spheres Due to Solar
Proton Events95% Confidence LevelValues Do Not Include Design MarginsAluminum
Shield Thickness1 SolarActive Year5 SolarActive Years7 SolarActive
Yearsg/cm2mmmilskrads-sikrads-sikrads-si0.030.114.379.06E+012.92E+023.72E+020.040.155.836.89E+012.22E+022.82E+020.050.197.295.41E+011.71E+022.17E+020.060.228.754.64E+011.47E+021.87E+020.080.3011.673.68E+011.15E+021.44E+020.100.3714.583.00E+019.31E+011.15E+020.150.5621.872.23E+018.24E+011.06E+020.200.7429.161.78E+017.19E+019.36E+010.301.1143.741.14E+014.69E+016.07E+010.401.4858.318.37E+003.45E+014.45E+010.501.8572.916.18E+002.57E+013.32E+010.602.2287.485.04E+002.09E+012.70E+010.802.96116.653.53E+001.50E+011.96E+011.003.70145.832.69E+001.17E+011.53E+011.254.63182.282.04E+009.21E+001.21E+011.505.56218.741.72E+008.09E+001.08E+011.756.48255.161.48E+007.32E+009.89E+002.007.41291.611.33E+006.88E+009.37E+002.509.26364.531.05E+005.74E+007.98E+003.0011.11437.408.64E-014.85E+006.86E+003.5012.96510.246.91E-013.95E+005.59E+004.0014.81583.075.60E-013.23E+004.60E+004.5016.67656.304.45E-012.56E+003.65E+005.0018.52729.133.60E-012.06E+002.93E+005.5020.37801.973.08E-011.77E+002.51E+006.0022.22874.802.53E-011.45E+002.05E+006.5024.07947.642.13E-011.22E+001.72E+007.0025.931020.871.83E-011.04E+001.47E+007.5027.781093.701.57E-018.97E-011.26E+008.0029.631166.541.39E-017.88E-011.11E+008.5031.481239.371.21E-016.90E-019.72E-019.0033.331312.201.07E-016.11E-018.62E-019.5035.191385.439.32E-025.34E-017.55E-0110.0037.041458.277.84E-024.51E-016.40E-0112.5046.301822.835.69E-023.28E-014.64E-0115.0055.562187.404.18E-022.41E-013.41E-0120.0074.072916.142.44E-021.41E-011.99E-0125.0092.593645.281.55E-028.88E-021.26E-0130.00111.104374.021.10E-026.33E-028.96E-02
Page 37
A-8Table A8Integral LET for Interplanetary Galactic Cosmic Rays (Z=1-92)100 mils
Aluminum ShieldingValues Do Not Include Design MarginsLETLET FluenceLETLET
FluenceMeV*cm/mg#/sqcm/dayMeV*sqcm/mg#/sqcm/daySolar MinimumSolar
Maximum1.00E-034.25E+051.00E-031.54E+051.65E-034.24E+051.65E-031.54E+051.69E-033.29E+051.69E-031.07E+051.70E-033.04E+051.70E-039.42E+041.72E-032.84E+051.72E-038.46E+041.77E-032.54E+051.77E-037.02E+041.81E-032.30E+051.81E-035.98E+041.85E-032.12E+051.85E-035.20E+041.91E-031.90E+051.91E-034.34E+041.98E-031.72E+051.98E-033.75E+042.01E-031.67E+052.01E-033.59E+042.13E-031.46E+052.13E-033.05E+042.28E-031.27E+052.28E-032.69E+042.53E-031.07E+052.53E-032.39E+043.01E-038.29E+043.01E-032.11E+043.54E-036.87E+043.54E-031.98E+044.52E-035.55E+044.52E-031.88E+045.56E-034.90E+045.56E-031.83E+046.54E-034.58E+046.54E-031.82E+047.52E-032.76E+047.52E-037.46E+038.55E-032.13E+048.55E-035.04E+039.60E-031.75E+049.60E-033.97E+031.97E-027.02E+031.97E-021.88E+032.96E-025.07E+032.96E-021.63E+034.00E-024.33E+034.00E-021.55E+035.04E-023.81E+035.04E-021.43E+036.00E-023.50E+036.00E-021.36E+036.97E-022.91E+036.97E-021.08E+038.01E-022.66E+038.01E-021.01E+039.00E-022.40E+039.00E-029.12E+021.01E-012.23E+031.01E-018.74E+022.00E-019.84E+022.00E-013.59E+024.02E-014.33E+024.02E-011.52E+02
Page 38
A-9Table A8 (Continued)Integral LET for Interplanetary Galactic Cosmic Rays
(Z=1-92)100 mils Aluminum ShieldingValues Do Not Include Design MarginsLETLET
FluenceLETLET FluenceMeV*cm/mg#/sqcm/dayMeV*sqcm/mg#/sqcm/daySolar MinimumSolar
Maximum6.03E-012.90E+026.03E-011.10E+027.96E-012.23E+027.96E-018.84E+011.00E+001.79E+021.00E+007.22E+012.01E+003.39E+012.01E+005.88E+003.02E+001.43E+013.02E+002.03E+003.99E+007.76E+003.99E+001.02E+005.03E+004.59E+005.03E+005.81E-015.99E+003.07E+005.99E+003.80E-018.00E+001.55E+008.00E+001.90E-011.01E+019.00E-011.01E+011.10E-011.11E+017.17E-011.11E+018.75E-021.20E+015.76E-011.20E+017.04E-021.30E+014.67E-011.30E+015.71E-021.40E+013.85E-011.40E+014.72E-021.50E+013.16E-011.50E+013.88E-021.60E+012.61E-011.60E+013.20E-021.70E+012.20E-011.70E+012.71E-021.80E+011.85E-011.80E+012.27E-021.91E+011.54E-011.91E+011.89E-022.00E+011.30E-012.00E+011.60E-022.49E+014.45E-022.49E+015.50E-033.00E+016.27E-043.00E+018.18E-053.49E+016.86E-053.49E+011.06E-054.01E+014.18E-054.01E+016.50E-064.50E+012.83E-054.50E+014.42E-065.00E+012.00E-055.00E+013.13E-065.06E+011.92E-055.06E+013.00E-065.55E+011.34E-055.55E+012.11E-066.02E+019.38E-066.02E+011.49E-066.53E+016.32E-066.53E+011.01E-067.00E+014.40E-067.00E+017.01E-077.50E+012.83E-067.50E+014.52E-078.04E+011.65E-068.04E+012.63E-078.52E+017.71E-078.52E+011.23E-079.03E+011.94E-079.03E+013.10E-089.57E+012.88E-089.57E+014.60E-091.00E+021.19E-081.00E+021.89E-091.01E+025.27E-091.01E+028.41E-101.03E+022.54E-091.03E+024.05E-10
Page 39
A-10Table A9Integral LET for the October 1989 Solar Particle Event (Z=1-92)100
mils Aluminum ShieldingValues Do Not Include Design MarginsLETLET FluenceLET
FluenceLET FluenceMeV*cm2/mg#/cm2/s#/cm2/s#/cm2/sAverage Over PeakAverage Over
Worst DayAverage Over Worst
Week1.00E-031.93E+055.21E+041.15E+042.01E-031.93E+055.21E+041.15E+043.01E-031.93E+055.20E+041.14E+044.02E-031.92E+055.17E+041.13E+045.01E-031.90E+055.11E+041.11E+046.03E-031.86E+055.02E+041.08E+047.02E-031.82E+054.90E+041.05E+047.97E-031.77E+054.76E+041.01E+048.95E-031.71E+054.60E+049.68E+031.01E-021.64E+054.40E+049.19E+031.99E-029.60E+042.55E+045.07E+032.99E-025.39E+041.43E+042.78E+034.00E-023.23E+048.56E+031.65E+034.98E-022.11E+045.59E+031.07E+036.00E-021.45E+043.84E+037.33E+026.97E-021.06E+042.81E+035.34E+028.01E-027.91E+032.09E+033.96E+029.00E-026.16E+031.63E+033.08E+029.99E-024.90E+031.29E+032.44E+022.00E-019.50E+022.51E+024.67E+013.01E-013.15E+028.31E+011.53E+014.02E-011.25E+023.32E+016.08E+005.01E-013.82E+011.01E+011.80E+006.03E-011.86E+014.94E+008.78E-017.01E-011.35E+013.58E+006.52E-018.05E-019.85E+002.62E+004.91E-019.04E-017.55E+002.02E+003.87E-011.00E+005.88E+001.57E+003.10E-012.01E+007.49E-012.06E-015.99E-023.02E+004.11E-011.13E-013.33E-023.99E+002.64E-017.29E-022.14E-025.03E+001.74E-014.80E-021.42E-026.06E+001.21E-013.36E-029.92E-037.04E+008.68E-022.40E-027.11E-038.00E+006.39E-021.77E-025.26E-038.99E+005.04E-021.40E-024.13E-031.01E+013.85E-021.07E-023.15E-032.00E+015.75E-031.60E-034.63E-042.52E+012.14E-035.95E-041.72E-04
Page 40
A-11Table A9 (Continued)Integral LET for the October 1989 Solar Particle Event
(Z=1-92)100 mils Aluminum ShieldingValues Do Not Include Design MarginsLETLET
FluenceLET FluenceLET FluenceMeV*cm2/mg#/cm2/s#/cm2/s#/cm2/sAverage Over
PeakAverage Over Worst DayAverage Over Worst
Week3.00E+011.83E-055.10E-061.55E-063.53E+017.23E-072.01E-077.14E-084.01E+013.26E-079.08E-083.43E-084.50E+011.95E-075.44E-082.12E-085.00E+011.36E-073.78E-081.48E-085.55E+018.43E-082.35E-089.31E-096.02E+014.92E-081.37E-085.58E-096.53E+013.28E-089.12E-093.75E-097.00E+012.49E-086.92E-092.84E-097.50E+011.80E-085.00E-092.04E-098.04E+011.20E-083.34E-091.36E-098.52E+016.69E-091.86E-097.56E-109.03E+012.03E-095.64E-102.29E-109.46E+011.33E-103.71E-111.51E-111.00E+025.01E-111.39E-115.66E-121.01E+022.22E-116.19E-122.51E-121.03E+021.07E-112.99E-121.21E-12
Page 41
A-12Table A10Differential Fluxes from Solar Proton Events100 mils Aluminum
Shielding, CREME96Note: Spectra were cut off at E =1 MeV and E=1000 MeVValues Do
Not Include Design MarginsEnergyProton FluxProton FluxProton
FluxMeV#/cm2/s#/cm2/s#/cm2/sAverage Over PeakAverage Over Worst DayAverage Over
Worst
Week1.001.75E+034.62E+028.85E+012.002.68E+037.09E+021.36E+023.023.47E+039.17E+021.76E+024.044.11E+031.09E+032.09E+025.044.62E+031.22E+032.36E+026.035.03E+031.33E+032.58E+027.025.33E+031.41E+032.75E+028.065.56E+031.47E+032.88E+029.005.69E+031.51E+032.96E+0210.055.76E+031.53E+033.01E+0214.995.41E+031.44E+032.92E+0220.034.50E+031.21E+032.52E+0224.983.57E+039.65E+022.07E+0230.312.73E+037.40E+021.64E+0235.272.11E+035.75E+021.31E+0240.491.61E+034.42E+021.04E+0250.509.91E+022.73E+026.79E+0160.436.33E+021.75E+024.58E+0170.334.20E+021.17E+023.20E+0179.632.94E+028.18E+012.33E+0190.172.03E+025.65E+011.68E+01100.691.44E+024.01E+011.24E+01150.253.84E+011.06E+013.80E+00200.771.39E+013.79E+001.50E+00299.593.32E+008.62E-013.88E-01400.311.16E+002.85E-011.39E-01499.234.97E-011.16E-015.96E-02605.642.07E-014.64E-022.54E-02704.941.10E-012.48E-021.44E-02798.176.61E-021.48E-029.03E-03903.743.95E-028.88E-035.66E-03995.412.65E-025.96E-033.94E-03