Transcript Document

UTILIZING SPENVIS FOR EARTH ORBIT
ENVIRONMENTS ASSESSMENTS: RADIATION
EXPOSURES, SEE, and SPACECRAFT CHARGING
Brandon Reddell and Bill Atwell
THE BOEING COMPANY
NASA Systems
Houston, TX 77059 USA
SPENVIS & GEANT4 Workshop
Leuven, Belgium
3 - 7 October 2005
ABSTRACT
The SPENVIS, developed by the Belgium Institute of Aeronomy
(BIRA), Brussels, Belgium, has been utilized to generate trapped
proton and electron particle spectra for low-earth (LEO), mediumearth (MEO) and geostationary orbits (GEO) and to perform
comparisons/benchmarking for several high-energy particle
transport codes. A discussion of the proton and electron spectra
and transport codes used in this study is presented. Results of the
absorbed dose calculations and code comparisons using aluminum
shielding are presented and discussed in detail. An example of a
single event effects (SEE) analysis for the International Space
Station (ISS) internal and external computers is discussed.
Additionally, the application of SPENVIS to calculate spacecraft
charging is also discussed in relation to the ISS. A comparison of
the SPENVIS predicted structure potential with the Boeing ISS
Plasma Interaction Model (PIM) prediction and measured data from
the Floating Potential Probe (FPP) is shown.
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Outline of Talk
 Application of SPENVIS to generate trapped electron and
proton spectra for various near-Earth orbits
 Present dose comparisons for benchmarking radiation
transport codes
 MULASSIS/GEANT4, FLUKA, MCNPX, Shieldose 2, CEPXS
 Other SPENVIS options under consideration/or being used
by the Boeing ISS Environments Group
 Single Event Effects
 ISS vehicle structure charging predictions
 Comparison with Boeing ISS Plasma Interaction Model predictions
and on-orbit data
 Conclusions
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NEAR-EARTH REGIONS
 LOW-EARTH ORBIT (LEO) – Typical ISS orbit
 ~ 400 km X 51.6 deg
 MEDIUM-EARTH ORBIT – Global Positioning
Satellite (GPS) Orbit
 20,200 km x 55 deg
 GEOSTATIONARY ORBIT – 160 deg W long.
 ~36,000 km x ~0 deg
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LEO PROTON & ELECTRON SPECTRA
 AP-8MIN PROTON INTEGRAL & DIFFERENTIAL
SPECTRA
 ISS ORBIT: 400 KM X 51.6 DEG
 EPOCH: JUNE 2007
 AE-8MAX ELECTRON INTEGRAL &
DIFFERENTIAL
 ISS ORBIT: 400 KM X 51.6 DEG
 EPOCH: JAN. 2012
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LEO AP-8MIN PROTON INTEGRAL & DIFFERENTIAL SPECTRA
LEO AP-8MIN Proton Spectra
400 km x 51.6 deg - Epoch: June 2007
1.E+09
1.E+08
Integral & Diff. Flux, / day
Integral
Differential
1.E+07
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
0
100
200
Proton Energy, MeV
300
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LEO AE-8MAX ELECTRON INTEGRAL & DIFF. SPECTRA
LEO AE-8MAX Electron Spectra
400 km x 51.6 deg - Epoch: Jan. 2012
1.E+11
Integral & Diff. Flux, / day
1.E+10
Integral
1.E+09
Differential
1.E+08
1.E+07
1.E+06
1.E+05
1.E+04
1.E+03
0
1
2
3
4
5
6
Electron Energy, MeV
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MEO AE-8MAX ELECTRON DIFFERENTIAL SPECTRUM
Diff. Flux, #/cm2-MeV-day
MEO AE-8MAX Electron Diff. Spectrum
GPS Orbit - 20,200 km x 55 deg
1.E+14
1.E+13
1.E+12
1.E+11
1.E+10
1.E+09
1.E+08
1.E+07
1.E+06
1.E+05
1.E+04
1.E+03
0
2
4
Electron Energy, MeV
6
8
MEO AP-8MIN PROTON
DIFFERENTIAL SPECTRUM
Diff. Flux, #/cm2-MeV/day
MEO AP-8MIN Proton Diff. Spectrum
GPS Orbit
1.E+14
1.E+13
1.E+12
1.E+11
1.E+10
1.E+09
1.E+08
1.E+07
1.E+06
1.E+05
1.E+04
0
1
2
3
4
Proton Energy, MeV
5
6
7
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GEO AE-8MAX INTEGRAL & DIFF. ELECTRON SPECTRA
160 deg W long. – Epoch: Jan. 2012
GEO AE-8MAX Electron Spectra
160 deg W long. - Epoch Jan. 2012
1.E+14
Integral & Diff. Flux, #/cm 2-day & #/cm 2-MeV/day
Integral
1.E+13
Differential
1.E+12
1.E+11
1.E+10
1.E+09
1.E+08
1.E+07
1.E+06
1.E+05
0
1
2
3
Electron Energy, MeV
4
5
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COMPUTER CODES
 MULASSIS / GEANT 4
 3-D Monte-Carlo transport code
 Hadronic, Electromagnetic, Low-Energy Neutron Physics
 FLUKA
 3-D Monte-Carlo transport code
 Precision Physics Default, with electromagnetic and low
energy neutrons
 SHIELDOSE 2
 Uses pre-calculated, mono-energetic depth-dose data for an
isotropic, broad-beam fluence of radiation incident on uniform
aluminum plane media.
 Proton transport considers Coulomb interactions only (no
nuclear interaction), electron transport with bremsstrahlung
 MCNPX
 3-D Monte-Carlo transport code
 For this study, only electron transport considered, including
electromagnetic effects.
 CEPXS
 1-D planar-geometry discrete ordinates code for coupled
photon-electron transport
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LEO Proton Dose Comparisons
200 MeV Proton
incident on 1.0 g/cm2
Aluminum Slab
1
Mulassis/G4
FLUKA
Shieldose 2
Dose Rate, rad (Si) / day
0.1
0.01
0.001
0.0001
0.01
0.1
1
10
Al Shielding Thickness, g/cm2
100
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LEO Electron Dose Comparisons
1.0 MeV Electron
incident on 1.0 g/cm2
Aluminum Slab
100
Mulassis/Geant4
FLUKA
Dose Rate, rad (Si) / day
10
Shieldose 2
1
0.1
0.01
0.001
0.01
0.1
1
Al Shielding Thickness, g/cm2
10
13
MEO Electron Dose Comparisons
1.E+05
Mulassis/G4
FLUKA
Dose Rate, rad (Si) / day
1.E+04
Shieldose 2
1.E+03
1.E+02
1.E+01
1.E+00
1.E-01
0.01
0.1
1
Al Shielding Thickness, g/cm2
10
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GEO Electron
Dose Comparisons - 1
Geosynchronous Orbit - Electrons
1.00E+05
SD2
MCNPX
CEPXS
Mulassis/G4
FLUKA
Dose Rate, rads Si /day
1.00E+04
1.00E+03
1.00E+02
1.00E+01
1.00E+00
1.00E-01
0.01
0.10
1.00
Al Thickness, g/cm
10.00
2
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GEO Electron Dose Comparisons - 2
GEO Comparisons
1.00E+05
MCNPX
Mulassis/G4
FLUKA
1.00E+04
Dose Rate, rads Si /day
1.00E+03
1.00E+02
1.00E+01
1.00E+00
1.00E-01
1.00E-02
0.01
0.10
1.00
Al Thickness, g/cm
10.00
2
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Single Event Effects
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ISS Single Event Upset Observations
ISS
Orbit
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ISS Single Event Upset Observations
S1-1 MDM-10
S0-1 MDM-10
S1-2 MDM-4
S0-2 MDM-10
P1-1 MDM-4
P1-2 MDM-10
US Laboratory Module
MDM-DRAM
Measured SEU
Count/238 days
SEFA SEU
Count/238 days
FOM SEU
Count/238 Days
Lab-1 40 g/cm2
488
287
83
Lab-3 40 g/cm2
490
287
83
P1-2: 10 g/cm2
536
6202
1647
S1-1: 10 g/cm2
488
6202
1647
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ISS Spacecraft Charging
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ISS Vehicle Charging
 Various models available to compute floating potential of
structure with respect to plasma
 SOLARC, PIX2, thin sheath, thick sheath models for solar array and
structure
 SOLARC gives best correlation to observed floating potential and Boeing
ISS PIM results
 SOLARC only accounts for solar array charging (i.e. no magnetic induction)
FPP Unit
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FPP Potential Data (April 11, 2001)
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PEAK 1
FPP
Eclipse
Sun
PEAK 2
PEAK 3
Voltage (-V)
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PCU OFF
15
PEAK 4
PEAK 5
PEAK 6
10
5
0
12:00
14:00
16:00
18:00
20:00
22:00
Time (GMT)
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Potential Map for ISS Stage 11A
Corresponding to April 11, 2001 (FPP Peak 1) Conditions
Potential (V)
Vmin = -31.1V
Vmax = -18.3V
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ISS Potential Comparison
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FPP Data
PIM - 23m2
SPENVIS/SOLARC
Voltage (-V)
20
10
0
12:30
13:00
13:30
Time (GMT)
14:00
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Spacecraft Charging
 For LEO, spacecraft charging is highly dependent on
plasma temperature, density, and geomagnetic field
 For these reasons, a probabilistic approach must be
used to address spacecraft charging:
 Models like the International Reference Ionosphere (IRI-2001) are
climatological in nature and provide average properties; not the
short transients that occur near eclipse exit
 The SPENVIS spacecraft charging models allow the
user to input plasma temperature and density to
compute floating potential – only compute solar array
charging
 SPENVIS will need to access a plasma database of
measured/known values to calculate spacecraft
charging
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Spacecraft Charging
For predictions, known
plasma parameters must
used to simulate transient
plasma conditions
Climatological models do
not predict extreme
plasma conditions
properly
PIM Results
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CONCLUSIONS
 SPENVIS was utilized to generate trapped electron and proton spectra
for LEO, MEO, and GEO
 Various computer codes were used to transport these spectra to
compute absorbed dose
 Dose rates computed in thin silicon detector behind finite & semiinfinite slab aluminum shielding
 For all three regimes, the transport codes generally agree to within
10-15% of each other
 Some deviations at extremely thin and extremely thick regions
 Can infer differences in radiation transport model physics
 SPENVIS can be used to study Single Event Effects
 SPENVIS needs a choice of GCR models so that the user can
generate preferred spectra
 i.e. CREME 96 or Badhwar-O’Neil GCR Model
 Recommend adding Figure of Merit (FOM) technique to SPENVIS
 SPENVIS could be used to study spacecraft charging provided
user knows a priori plasma conditions
 SPENVIS needs a geomagnetic field induced potential (vxB·L)
option/model. This is important for large spacecraft
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