A three-dimensional geometry/mass model of LDEF is under development for ionizing radiation analyses. This model, together with ray tracing algorithms, is being programmed for use both as a stand alone code in determining three-dimensional shielding distributions at dosimetry locations and as a geometry module that can be interfaced with radiation transport codes

Armstrong, T. W.

Colborn, B. L.

English

NASA Technical Reports Server

N92-23
LDEF GEOMETRY]MASS MODEL FOR RADIATION ANALYSES*
305
B. L. Colborn and T. W. Armstrong
Science Applications International Corporation
4161 Campus Point Court, San Diego, CA 92121-1513
Phone: 619/458-5282, Fax: 619/458-5067
SUMMARY
A three-dimensional geometry/mass model of LDEF is under development for
ionizing radiation analyses. This model, together with ray-tracing algorithms, is being
programmed for use both as a stand-alone code in determining 3-D shielding distributions
at dosimetry locations and as a geometry module that can be interfaced with radiation
transport codes.
INTRODUCTION
To aid in the interpretation of ionizing radiation dosimetry data, and to obtain more
accurate comparisons of dosimetry measurements with model predictions, a three-
dimensional geometry/mass model of the Long Duration Exposure Facility (LDEF)
satellite is under development. The modeling approach and level of detail being
incorporated is described below.
APPROACH
Three general categories of LDEF components are defined for modeling purposes
(fig. 1). The major structural components of the spacecraft are being modeled
individually, as illustrated in fig. 2. The mass of other components of the spacecraft
("miscellaneous" category of fig. 1, which amounts to about 5% of the total mass) is
combined with the mass of the larger components, except that the thermal covers are
modeled individually. The third category is the experiment trays, containing the tray itself
and the contents of the experiment. Since the weight of individual experiments varies
substantially (fig. 3), each of the 84 experiment trays is modeled separately.
For experiment trays containing radiation dosimetry, "detailed" modeling of major
components within the tray is being performed so that local shielding variations in the
vicinity of the dosimeters can be accounted for (fig. 4). For trays not containing ionizing
radiation dosimeters, only the volume and mass of the trays are preserved. The contents
of these "generic" trays are modeled as homogeneous aluminum of reduced density.
*Work supported by NASA Marshall Space Flight Center, Huntsville, AL, Contract NAS8-35866.
PRF.CEDING PAGE BLANK NOT FILMED
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Inputdatafor themodelis basedon informationprovidedby theLDEF Project
Office (J.Jones)andothersat LaRC(R. Shearer),includingengineeringdrawingsof the
spacecraftandpre-flightweightestimatesandlayoutsof individualexperiments,and
informationoncomponentlayoutsandmaterialsdescriptionsobtainedfrom individual
experimenters.
Thecombinatorialgeometrymethodologyis beingused. In thismethodBoolean
logic is appliedto combinedescriptionsof simplebody shapesto simulatecomplex
geometries.
The modelis beingprogrammedto allowoperationin eitherof twomodes: asa
geometrymodulewhichcanbeinterfacedwith radiationtransportcodes,andasastand-
aloneprogramwith ray tracing(fig. 5). In this lattermode,thearealdensityandmaterial
compositionalongraysemanatingfrom specifiedpointscanbecomputedto form a3-D
grid of shieldingvariationsaboutthepoint. Fordosimeterswhereindividual particle
tracksaremeasured,thisray-tracingmodewill allow raysto bestartedthathavedirections
correspondingto thetrackdirection,sothematerialtraversedin reachingthedosimetercan
beestimatedfor individualtracks.
STATUS
At presentheLDEF spacecraftstructurewith genericexperimentrayshasbeen
modeled.Detailedmodelingfor severalof thetrayscontainingionizingradiation
dosimeters(ExperimentsP0004,P0006,andM0004)is in progress.
362
Ca teg ory
STRUCTURE
MISCELLANEOUS
EXPERIMENTS
No. Wetghi Weight
Component Places (Ibs.} %
Center Ring 1 2,073 9.7%
Longerons 24 2,280 10.7%
End Frames 2 1,374 6.4%
Diagonal Tubes 8 926 4.3%
Intercostal Rings 72 758 3.5%
Trunions,Pins, & Scuff Plates 10 501 2.3%
End Support Beams 5 285 1.3%
TOTAL STRUCTURE: 8,197 38.3%
Batteries 2 100 0.5%
Initiate Electronics 1 105 0.5%
Wiring 100 0.5%
Nuts and Bolts 200 0.9%
Damper Assembly 1 62 0.3%
Thermal Covers (Ends) 12 154 0.7%
Ballast Plates 11 365 1.7%
TOTAL MISCELLANEOUS: i-_(386 5,1<'1o
Experiment Components + Trays 84 12,110 56.6°1,
ModellnQ Approach
Modeled as individual component.
Modeled as individual components.
Modeled as individual components,
Modeled as individual components.
Modeled as individual components.
Modeled as individual components.
Modeled as individual components.
Included as part of earth-end support beam weight.
Included as part of center ring weight.
Included as part of center ring weight.
Included as part of center ring weight.
Included as part of space-end support beam weight.
Modeled as individual components.
Included as part ot end frames.
Modeled each experiment tray separately, with
individual experiment weights preserved. ModeNng
detail for components varies with experiment type.
TOTAL LDEF WEIGHT: 21_393 100.0%
Fig. 1. Level of detail incorporated in LDEF geometry/mass model.
!2
11_"F_:::C_*_ 1 Er',d Frames 1
9 3
_ _ End Support Beams "k_ -,,
6
Ear_ End
12
Longerons
Diagonal Tubes
Center Ring Intercostal Rings
F---ql I' 1 I I
II It
h L I
Fig. 2. Model of LDEF spacecraft structure.
363
Weight
in Ibs
Fig. 3. Weights of individual experiments on LDEF.
I
2
3
4
5
!°
7
8
9
tO
I1
12
BAY
A B C D E F
Earth End SpaDe End
R SOD01 Experiments
A0178 Experiments
_] DetBiled Modeling of Experiments contain9 IR Dosimeters
Olhers - Homogenized Aluminum
Level of Detail for Modeling Experiments."
No.
Trays Model Ex pe rim e nee
26 AI plata 50001: Space Debris (LaRC)
16 AI,plaslic plates A0178: URra-heavy Cosmic-Ray Expt (Dublin inst. ESTEC)
1 3 "detailed" Experiments containing IR dosimetry - see NOTE
29 homogenized AI (all others)
NOTE: Trays Contsining IR Dosirnetery for Detailed Modeling are;
Trey
Bay-Row
C.2, G-2
C-3. C-9
B-3
H-3. H-12
0-3,0-_I,G- 12
E-6
D-3,D-B,O-9
F*8
C-2
F2
F-2
A-0015
A-0114
A-013B
M0001
M0002-1
M0002-2
M0003
M0004
M0006
P0004
P0006
Experiment
Biostack (DFVLR)
Atomic Oxygen (UAH, MSFC)
Dptical Fibers (CERT/ONERA - DERTS)
Heavy Ions (NRL)
Trapped Proton Space (AFGPL.MSFC. et al
Heavy Cosmic-Ray Nuclei (U Keil)
Spaca Envr Effects on bails (Aerospace)
Space Envr Effects on Optics (AFWL)
Space Envr Effaces (AFTAC. Grumman)
SEEDS
LET &cectrum Mete (Univ SF. MSFC)
Dosimetry
TL_s, PNTD'$
Activation Samples
TLD'S
PNT_s
PNT_s,TLD'$,Act
PNTD's
TLD's
TLD's, PNTD's
TLD's
TL_s, PNTO'$
TLD's, PNT_a,
RSS. & A_ Samples
Fig. 4. Modeling approach for LDEF experiments.
364
LDEF Geometry/Mass Model
(Combinatorial Geometry Module)
3-D Transport Codes
(e.g., HETC Monte Carlo Code)
1-D Transport Codes with
3-D Solid Angle Sectoring
Shielding Distribution
for 3-D Ray Grid
Fig. 5. Utility of LDEF geometry/mass model.
365



LDEF geometry/mass model for radiation analyses

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