GLAST Large Area Telescope LAT Pre-Shipment Review Thermal Vacuum Test Jesse Armiger

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope LAT Pre-Shipment Review Thermal Vacuum Test Jesse Armiger Thermal Vacuum Test Director Stanford Linear Accelerator Center Thermal Vacuum Test

2. Agenda • Test Overview and Major Test Event Log • Compliance To Requirements • Correlation Results • Thermal Test Observations • Summary Thermal Vacuum Test

3. Test Picture Thermal Vacuum Test

4. Test Overview Thermal Vacuum Test

5. Compliance to Requirements • LAT successfully completed Thermal Vacuum Testing • 40 day test was successfully completed with only EGSE issues • Successfully tested LAT at Proto-Qual levels • Verified thermal subsystem performance • Heaters • Heat pipes • Temperature sensors • Thermal Interface/Unit Mounting • Thermal analysis correlation • No abnormal observations • Complete by October 30 Thermal Vacuum Test

6. Heater System Verification • Survival heater system maintained all temperatures within limits during Survival Thermal Balance • Unregulated and regulated feeds at minimum voltage • Unregulated feed at 25v and regulated feed at 27v • Grid heaters cycled at primary set points • Radiator Antifreeze heater duty cycle under review • Demonstrated primary VCHP heaters could close Radiators at 70% power • Functionally demonstrated all primary and redundant Radiator antifreeze and Grid heaters • Demonstrated TCS could maintain RIT at all operational levels Thermal Vacuum Test

7. Heat Pipes and Thermal Interfaces • Heat Pipes • All Heat Pipes functioned normally • DSHP and XLATs operated as expected • VCHPs opened/closed Radiators as designed • Interfaces • No baseplate outliers Thermal Vacuum Test

8. Unit Temperature Distribution Hot Thermal Balance Thermal Vacuum Test

9. Preliminary Correlation 1/2 • Test results show good correlation between sink temperature predictions and input Watrod power • ACD model received from GSFC uncorrelated – ACD MLI effectiveness needs evaluation • ACD temperatures have impact on LAT correlation • Generally ACD tile temperatures higher than predictions (>5o C) in all cases • Higher tile temperatures lead to higher tracker temperatures • Grid heaters need to be modeled with individual thermostat set points for each circuit Thermal Vacuum Test

10. Preliminary Correlation 2/2 • Hot Case - Temperatures generally lower than predicted • Cold Case – • Temperatures generally higher than predicted • Radiator Anti-freeze and grid survival heaters off • VCHP heaters • 9.7 watts to maintain RIT between -6oC and -5oC (23% duty cycle) • Locked on to maintain RIT between -1oC and 0oC • Survival Mode • Temperatures generally higher than predicted • Radiator Anti-freeze and grid survival heater use about 7 amps • Heater Power use higher than predicted Thermal Vacuum Test

11. Test Predictions vs. Actuals Thermal Vacuum Test

12. Thermal Test Observations • ACD temperature sensor exceeded its red alarm limit of 40C (unit proto-qual = 40C) • This sensor reached a maximum of 42C; the temperature excursion may have been caused by sensor malfunction • This was not unexpected because the ACD is bounded by a thermal blanket on one side and Tracker Towers with goal temperatures of 40-45C • The ACD project manager has indicated that this temperature poses no risk to the ACD • Recommend an ACD red limit of 45C for the observatory test Thermal Vacuum Test

13. Thermal Test Observations • LAT start up sequence from cold survival NCR #? • The normal start up sequence involves incrementally powering up the LAT in a manner which does not exceed the power budget • The planned sequence involved powering up the TCS last but it turned out that this step had to be performed earlier in order to stay within the budget • This minor change will be documented and implemented in the normal turn on sequence to be performed during observatory level testing Thermal Vacuum Test

14. Summary • The LAT thermal vacuum test was accomplished ahead of schedule and without any major incident. Three thermal balances (hot, cold and survival) and four thermal cycles were performed. • Thermal data readout by VSC was very noisy and inaccurate; this caused hardship during the test. • Minor incidents were corrected efficiently. • Complete LAT Thermal Vacuum test report by October 31. • Include thermal model correlation Thermal Vacuum Test

15. Major Thermal Vacuum Test Events 1/2 Performance Testing Thermal Vacuum Test

16. MajorThermal Vacuum Test Events 2/2 Thermal Cycling Thermal Vacuum Test