1. GLAST Large Area Telescope:
Gamma-ray Large Area Space Telescope
GLAST Large Area Telescope:
Mechanical Systems Peer Review
March 27, 2003
Section Radiator Thermal Design
Liz Osborne
Lockheed Martin
Thermal Engineer

2. Topics Requirements Thermal Design Overview
Thermal Design Environments
Orbital Environment
Spacecraft Interface
Thermal Control
Variable Conductance Heatpipes
Thermal Surfaces
Heaters
Thermal Model
Results
Hot Operation, Cold Operation, Survival
Summary & Future Work

3. Driving Thermal Requirements
Based on: Radiator Level IV Design Specification, LAT-SS D6, Draft, Dated 5 Mar 2003
LAT Mechanical Systems Interface Definition Dwg, Radiator-LAT Interface, LAT-DS-01221, Draft, Dated 25 Feb 2003

4. Thermal Design Overview
Radiators
Two panels, parallel to the LAT XZ-plane
Size per panel: m x 1.56 m = 2.8 m2
Construction
Aluminum honeycomb structure
6 Variable-Conductance Heat pipes (VCHP’s) on each Radiator panel
Interface to XLAT CCHP’s and LAT DSHP’s at each Radiator Interface Temperature (RIT)
Provide active feedback control of grid temperature through VCHP’s
RIT (6 places)

5. Thermal Design Environments
Cold Orientation
Hot Orientation
Survival Orientation

6. Orbital Heatloads

7. Interface to Spacecraft & LAT
Solar Arrays strong influence on Radiators
Hot design: Arrays begin 0.52m from radiator
Orbit-average heatload on 1 radiator (to IRD spec) is 73W
Conservative design approach
Actual Spectrum Astro solar array design is 1.32m from radiator
Cold & Survival design: Arrays begin 1.32m from radiator
Corresponds with actual Spectrum Astro Design
Spacecraft mount points (2/radiator)
5W max total heat leak to Radiators
LAT mount points (2/radiator)

8. Thermal Control (1 of 3) VCHP’s
Interface to XLAT CCHP’s and LAT DSHP’s at each RIT
Removes 612W (hot) and 497W (cold) from instrument
Non-condensable gas mass, 0.42g (conservative)
Cold operation: Provides active feedback control of grid temperature through VCHP logic & heaters
Maintains RIT above –5 C
Hot operation: VCHP full open
RIT temperature not controlled
Survival: VCHP closed
Reservoir heaters on full to drive up gas front and close off pipe
Thermal Surfaces (5 yr EOL)
Radiator & Reservoirs: 10mil FOSR – Second Surface Aluminized Teflon
a/e: .08/.85 (BOL), .24/.85 (EOL)
Approved to withstand AO degradation
Radiator backside: MLI Blanket
e* range .01 to .03
Aluminized kapton, outer layer facing S/C
a/e: .12/.04 (BOL), .16/.04 (EOL)
RIT and transport of VCHP: MLI Blanket
No radiation included in thermal model

9. Thermal Control (2 of 3) Heaters Operational VCHP reservoirs Survival
3.5W each (27V), Total 42W 29V)
Feedback control from RIT
Survival
Operational heaters are switched on full
Anti-freeze heaters (condenser length)
4 total zones, 1 zone per 3 heatpipes
Controlled by thermostats and RTD’s
Enabled lower setpoints
Primary control set ON/OFF -62°C/-58°C
Redundant set ~4C lower with offset RTD’s

10. VCHP Thermal Control Heaters and Sensors
Thermal Control (3 of 3)
VCHP Thermal Control Heaters and Sensors
+Y Radiator Shown Only +Z +X +Y T
Zone 1
Zone 2
Heaters
Thermostat Controllers
RTD’s

11. Thermal Model Imbedded VCHP’s Reservoirs TSS Model
Surface model to calculate view factors and orbital fluxes
Thermal Synthesizer System, v.11C
Input: geometry, material properties, optical properties, environmental parameters, orbit definition
Output: RADKS (eAF), Heatrates (W), Conductances and Capacitances for input into SINDA Thermal Model
SINDA Model
Numerical network of capacitances & conductances
Cullimore & Ring SINDA/FLUINT 4.5
4710 Total Nodes (Radiators & VCHP’s)
Imbedded VCHP’s
Input: conductances, capacitances, interfaces, sources, heaters,
TSS outputs, VCHP logic
Output: temperatures, temperature stability, VCHP gas front,
Heatpipe loads, average heater power
Reservoirs

12. Thermal Results – Hot (1 of 3)
Steady State Orbit Average Heatmap for –Y Radiator

13. Thermal Results – Hot (2 of 3)
Reservoir Average Heater Power = 0 W

14. Thermal Results – Hot (3 of 3)
VCHP #2 Failure (worst case) increases max RIT temperature to +14°C

15. Thermal Results – Cold (1 of 3)
Reservoir Average Heater Power = 13 W

16. Thermal Results – Cold (2 of 3)
Snapshot Temperatures at time=410min
Reservoir Average Heater Power = 13 W °C
Radiator –Y VCHP’s
Radiator +Y VCHP’s 1 2
RIT 3 4 5 1 2
RIT 3 4 5
Transport
Transport
Condenser
Condenser
Reservoir
Reservoir

17. Thermal Results – Cold (3 of 3)

18. Thermal Results - Survival
Minimum VCHP temperature = -65 C
Reservoir heaters on full = 42W/27V (Max Temperature = 42 C)
Antifreeze heaters average power = 91W: with 30% margin =118 W
-Y Radiator
+Y Radiator
center pipes

19. Summary & Future Work Summary Future Work
Thermal design of Radiators presented
VCHP’s used to control the interface to the LAT
Thermal control surfaces optimize radiator and protect from environment & spacecraft
Operational Heaters have been sized for VCHP control
Survival Heaters maintain the VCHP’s above limits
Thermal analysis results presented
Hot: Max RIT temperature is +10 °C
HP Failure increases max RIT to +14°C
Cold: Min RIT temperature is –5 °C
Survival: Min RIT temperature is –20°C
Heaters maintain VCHP’s above –65°C
In compliance with the thermal requirements
Open TBD’s need resolution
Future Work
Update model as necessary
Run system engineering trade analyses
Nominal hot case, Rocking mode, Transition mode, NCG mass optimization, 10-yr mission
Finalize location and mount design of SS thermostats