GLAST Large Area Telescope:

1
GLAST Large Area Telescope Tracker
Subsystem WBS 4.1.4 2F Thermal Design Liz
Osborne Lockheed Martin Liz.Osborne_at_lmco.com
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 30C
• Survival -30 to 50C
• 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 (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 3C

Tracker Walls Not Shown
Tracker interface
Copper Straps
Grid interface
5
Thermal Model
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
0
5
10
15
1
6
11
2
7
3
X
6
Thermal Results Hot (1 of 3)
Steady State Temperatures
C

• Steady State Temperatures
• Max DT up wall is 6C (7C including entire
  tower)
• Max Temp, 24C
• Located at Bay 5, Top 5 Std Closeout
• Transient Temperatures
• Max Tracker Transient, 24C

Z
Y
15
0
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 4.4C
• Max Temp, 28.4C

Bay 4
Bay 5
Bay 6
9
Thermal Results - Cold

• Min Tracker Transient, -3C

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
• 4.4C 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