1. GLAST Large Area Telescope:
Gamma-ray Large Area Space Telescope
GLAST Large Area Telescope:
Tracker Subsystem
WBS 4.1.4
2F: Thermal Design
Liz Osborne
Lockheed Martin

2. Agenda Thermal Design Overview & Requirements Interface to Grid
Thermal Model
Results
Hot Operation, Cold Operation, Survival Minimum
Summary & Future Work

3. Thermal Design Overview
Requirements (check)
Operating: -15 to +30°C
Survival: -30 to +50°C
16 identical towers (25 trays each)
10.2W (hot) and 8.7W (cold) per tower, located on MCM boards
Primary heat path is from MCM closeouts on each tray to high conductivity walls (K13), down walls to Grid through heatstraps
High emissivity external surfaces promote radiation between towers and to ACD
cables

4. Interface to Grid Copper Straps
Copper straps (4 per tower) conduct Q from tower walls to the Grid
Between walls and bottom tray
Hot: 2.55W/strap
RTV interface at Tracker
Bolted (dry) at Grid
Interface Delta T is 3°C
Tracker Walls
Not Shown
Tracker interface
Copper Straps
Grid interface

5. Thermal Model SINDA/TSS Model 82 Nodes/Tower, 1312 total+Z
SINDA/TSS Model
82 Nodes/Tower, 1312 total
Trays are lumped into groups per tower
Top tray
Top 5 Standard Trays
Bottom 6 Standard trays
Heavy Trays
Standard No Converter trays
Bottom Tray
Each Tray Group consists of 1 Tray node, 4 closeout nodes (Q input), 8 wall nodes
Copper strap interface to Grid nodes +Y 12 8 13 4 9 14 5 10 15 1 6 11 2 7 3 +X

6. Thermal Results – Hot (1 of 3)°C
Steady State Temperatures
Steady State Temperatures
Max DT up wall is 6°C (7°C including entire tower)
Max Temp, +24°C
Located at Bay 5, Top 5 Std Closeout
Transient Temperatures
Max Tracker Transient, +24°C +Z +Y 15 +X
Internal View

7. Thermal Results – Hot (2 of 3)

8. Thermal Results – Hot (3 of 3)
Trade: Grid/Tower Interface failure, center tower (Bay 5) °C
DT steady state increase is 4.4°C
Max Temp, +28.4°C
Bay 4
Bay 5
Bay 6

9. Thermal Results - Cold
Min Tracker Transient, -3°C

10. Thermal Results - Survival
Minimum Tracker Survival Temperature is –24 °C

11. Summary & Future Work Summary Tracker Thermal Design Presented
Heat conducts from MCM boards to walls, down walls, through copper strap interface to Grid
In compliance with Requirements
4.4°C increase with complete failure at Grid/Tracker interface for hottest tower
Future Work
Update thermal model as necessary
Tracker wall material
Requirement
In Spec
With uncertainty
Design
Margin
Operational Temperature
-15/+30 C
-10/+25 C
-3 /+24 C
+7 /+1 C
Survival Temperature
-30/+50 C
-25/+45 C
-24/TBD C
+1 & heater margin/TBD C