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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
GLAST Thermal Model Overview
Jeff WangLockheed Martin Advanced Technology CenterLAT Thermal Systems Engineer
GammaGamma--ray Large ray Large Area Space Area Space TelescopeTelescope
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
LAT Thermal Systems OverviewLAT Thermal Systems Overview
012860.25208
Survival
W602523LAT Process Power
On-Orbit Thermal Environment and LAT Process Power
W/m2
W/m2Units
12860.25208
Cold
1419Solar Flux0.40Earth Albedo265Earth IRHot MLI thermal shielding surrounding
ACD, Grid Box, Electronics
X-LAT Plates shunt Electronics process power to Radiators
LAT Thermal OverviewLAT Thermal Overview
Active VCHP control allows for variable Radiator area to maintain constant interface temp to LAT
Total Max Power = 602 + 48 = 650 W
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Thermal System Detailed DesignThermal System Detailed Design
• Radiators– Two panels, parallel to the LAT XZ-plane– Size per panel: 1.85 m x 1.46 m = 2.7 m2
– Construction• Aluminum honeycomb structure
• 6 variable-conductance heat pipes on each Radiator panel
– Provide active feedback control of grid temperature through VCHP’s
• Heat Pipes– Design
• Constant-conductance heat pipes on the Grid Box
• Ammonia working fluid• Extruded aluminum• Multiple axial groove casings
– Top Flange Heat Pipes (not shown)• Isothermalize grid structure
– X-LAT Heat Pipes• Remove waste heat from electronics• Connect radiators for load-sharing
– Downspout Heat Pipes• Transport waste heat from grid to radiator
VCHPs
Down Spout Heat Pipes
Radiator and Heat Pipe DetailsRadiator and Heat Pipe Details
X-LAT Heat Pipes
Variable-Conductance Heat Pipes
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Radiator Hot Design Case Heat LoadsRadiator Hot Design Case Heat Loads
0
100
200
300
400
500
600
700
800
9000
900
1800
2700
3600
4500
5400
6300
7200
8100
9000
9900
1080
011
700
1260
013
500
1440
015
300
1620
016
818
Rad1 TotalRad2 TotalRad total(2)
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Thermal Design Changes Since DPDRThermal Design Changes Since DPDR• Radiators
– Moved Radiators closer to Grid to accommodate spacecraft concerns– Increased radiator area from 2.7 sq meters to 2.73 sq meters but added area
in inefficient locations(far from VCHPs)– Provide individual control of each VCHP reservoir-lessons learned from on
orbit experience– Due to lack of definition of minimum solar array view factor, asked for greater
survival heater power budget-affects cost, schedule of TCS components
• Tracker– Add high emissivity black paint to aluminum EMI shield on tracker composite
walls• Increases heat transfer to ACD and increases tile detector assembly
temperatures• Increase heat transfer among tracker towers and reduces the maximum
tracker temperature• ACD
– Change outside layer of LAT MLI blanket from FOSR to germanium black kapton
• Increases tile detector assembly temperatures• Increases maximum tracker temperature
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
LAT Instrument and Radiator Assembly Thermal ModelLAT Instrument and Radiator Assembly Thermal Model
• Combined TSS/SINDA Model consists of– External TSS from ACD TSS Model
• (64 surfaces, 2440/2752 active nodes)– Internal TSS includes internals from ACD
and LAT Grid and TKR’s– TSS radiators, XLAT, solar arrays and
vehicle• SINDA Model
– Consists of 11,617 nodes– ACD model from GSFC with Grid and TKR’s
removed (516 nodes)– LAT SINDA model generated from SLAC
ANSYS model (7969 nodes)– Radiator, X-LAT and solar array SINDA
nodes and conductors generated by LMMS
LAT Thermal Model TSS External GeometryLAT Thermal Model TSS External Geometry
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Tracker Thermal ModelTracker Thermal Model
• Current tracker thermal model not adequate– Does not account for radiation heat transfer – Current Thermal Model doesn’t converge during steady state
calculations • Can lead to error in temperature predictions if not understood• Very high conductors indicate some nodes should be lumped together• Some zero conductors
• Developing new thermal model of tracker– Will include radiation heat transfer between tracker with high
emissivity coating(black paint) on tracker walls– Model expected 1/15/03
• Confirmed thermal conductivity of tracker composite walls 297 w/m-K in the Z-direction; 147 w/m-K in plane perpendicular to Z
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Calorimeter Thermal ModelCalorimeter Thermal Model
• Detailed Calorimeter model developed to replace current ~200 node model in LAT– Will be correlated to upcoming component level test– Reduced model (15 nodes) developed for LAT thermal model
• Will be correlated with detailed model• Model due 11/15-currently scheduled for 11/22• Will use to confirm TV cycle time
N6 N4
N2
N3
N5 N1
N7
N8 N9 N11
N10
N12
N13
N15 X+
Y+
N14
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
CooldownCooldown of LAT in Thermal Vacuum Testof LAT in Thermal Vacuum Test
With VCHPs kept full open, it takes about 36 hours for the Tracker to reach its lower ATP limit. This also assumes the LAT is in flight configuration, i.e. MLI blankets, Radiators, etc. as designed for flight.
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Calorimeter Calorimeter CooldownCooldown--Current Model PredictsCurrent Model Predicts
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Electronics ModelingElectronics Modeling
• Current definition, used for Delta-PDR
Cold Case Power Dissipation Hot Case Power Dissipation
Bay 12SIU-A
Bay 13Empty
Bay 14Empty
Bay 15EPU-A
Bay 12SIU-A
Bay 13Empty
Bay 14Empty
Bay 15EPU-A
27.97 0 0 13.61 33.78 0 0 16.44
Bay 8SIU-B
Bay 9GASU
Bay 10GASU
Bay 11EPU-A
Bay 8SIU-B
Bay 9GASU
Bay 10GASU
Bay 11EPU-A
0 7.08 7.08 13.61 0 8.64 8.64 16.44-X Side Bay 4
Pwr Dist-BBay 5GASU
Bay 6GASU
Bay 7EPU-A
+X SideSun Side
-X Side Bay 4Pwr Dist-B
Bay 5GASU
Bay 6GASU
Bay 7EPU-A
+X SideSun Side
0 7.08 7.08 13.61 0 8.64 8.64 16.44
Bay 0Pwr Dist-A
Bay 1Empty
Bay 2EPU-B
Bay 3EPU-A
Bay 0Pwr Dist-A
Bay 1Empty
Bay 2EPU-B
Bay 3EPU-A
24.00 0 0 13.61 36.00 0 0 16.44
Ptot: 134.75 Ptot: 170.08TEM/TPS: 9.23 TEM/TPS: 13.02
P(tot): 282.43 P(tot): 378.38
Legend: Notes:GASU Global trigger, ACD, and Switching Unit 1. All power is in wattsSIU Spacecraft Interface UnitPwr Dist Power Distribution BoxEPU LAT Event Processor-A A-side, powered box-B B-side, unpowered cold box
LAT Top View
-Y SideLAT Radiator
+Y SideLAT Radiator
+Y SideLAT Radiator
-Y SideLAT Radiator
LAT Top View
LAT +X
LAT +Y
LAT +X
LAT +Y
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Electronics ModelingElectronics Modeling
• No detailed definition– Only preliminary mechanical layouts– Only preliminary footprints of specific electronics on X-LAT plate– Mechanical lead recently hired to work interface details
• Current definition will define X-LAT heat pipes– Need detailed definition of electronics box design by 12/20
Heat Flow From X-Lat HP's to RadiatorsV0 Combined_LAT_ACD_hot_xtrasol, Third Orbit
-60
-50
-40
-30
-20
-10
0
11212 12212 13212 14212 15212 16212 17212
Time (Seconds)
Hea
t Rat
e (W
atts
)
X-Lat1, Rad1
X-Lat1, Rad2
X-Lat2, Rad1
X-Lat2, Rad2
X-Lat3, Rad1
X-Lat3, Rad2
X-Lat4, Rad1
X-Lat4, Rad2
X-Lat5, Rad1
X-Lat5, Rad2
X-Lat6, Rad1
X-Lat6, Rad2
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
VCHP ModelingVCHP Modeling
• Lockheed Martin Software– Converted from heritage to Sinda format– Providing results consistent with Cullimore & Ring routine; will allow
use of commercial software for model delivery– Currently working VCHP control logic; expected by 12/20
• VCHP Modeling– Added reservoirs to TSS model; required for feedback control – Can evaluate hot design case; cold case evaluation difficult without
minimum solar array view factor
• VCHP Control– For normal operations, each heatpipe will be individually controlled
• Requires more heater zones and thermistors• Complicates control logic• necessary for control during all possible orientations(flight experience)
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Verification Test TemperaturesVerification Test Temperatures• Test temperatures set to exercise
subsystem design limits
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GLAST LAT Project LAT Systems Engineering Review, 11/19/02
Environmental Temperature LimitsEnvironmental Temperature Limits
Component Low Temp Limits (degC) High Temp Limits (degC) Survival (degC)Qual AT Operating Operating AT Qual Low High
Desired -40 -35 -30 +50 +55 +60 -40 +60
Tracker -30 -20 -15 25 30 50 -30 50Calorimeter -30 -20 -15 25 30 50 -30 50TEM* -40 -35 -30 50 55 60 -40 60EPU* -40 -35 -30 50 55 60 -40 60SIU* -40 -35 -30 50 55 60 -40 60Pwr Dist* -40 -35 -30 50 55 60 -40 60GASU* -40 -35 -30 50 55 60 -40 60BEA -25 -20 -15 30 35 40 -40 45TDA -50 -45 -40 35 40 45 -60 45Grid -40 -35 -30 30 35 40 -40 40CCHP's -40 -35 -30 30 35 40 -40 40VCHP's -35 -30 -25 30 35 40 -67 40Radiator Panels -72 -67 -62 50 55 60 -72 60
• Shooting for “Desired” temperature limits• Any deviations from desired limits requires a technical note justifying the change