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Jeff Wang LMCO LAT Thermal Engineer jeff.wang@lmco

Gamma-ray Large Area Space Telescope. LAT Thermal Systems Analysis. Jeff Wang LMCO LAT Thermal Engineer jeff.wang@lmco.com. Agenda. Introduction Design trade analyses performed and results Thermal systems overview Thermal parameters Requirements and interfaces

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Jeff Wang LMCO LAT Thermal Engineer jeff.wang@lmco

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  1. Gamma-ray Large Area Space Telescope LAT Thermal Systems Analysis Jeff Wang LMCO LAT Thermal Engineer jeff.wang@lmco.com

  2. Agenda • Introduction • Design trade analyses performed and results • Thermal systems overview • Thermal parameters • Requirements and interfaces • Analysis parameters, environments, and case definitions • Analysis update • Hot- and cold-cases analyses • Survival-case analysis • Other non-design case analyses • Failure-case analyses • Thermal Control System Design • Summary and Further Work

  3. LAT Thermal Systems Overview • Radiators • Two panels, parallel to the LAT XZ-plane • Size per panel: 1.82 m x 1.56 m = 2.84 m2 • Aluminum honeycomb structure • Heat Pipe design • Constant-conductance heat pipes on Grid Box • Ammonia working fluid • Extruded aluminum, with axial groove casings • Heat pipes • Variable-conductance Heat Pipes • 6 VCHP’s per Radiator panel • Provides feedback control of grid temperature • 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 Radiators MLI thermal shielding surrounding ACD, Grid Box, Electronics Down Spout Heat Pipes connect Grid to Radiators X-LAT Heat Pipes shunt electronics power to Radiators Active VCHP control allows for variable Radiator area to maintain constant interface temp to LAT LAT Thermal Overview

  4. Downspout and X-LAT Heat Pipes

  5. LAT Thermal System Schematic Diagram LAT Thermal Schematic Diagram

  6. Internal Thermal Design Changes Since Delta-PDR The following design changes have been incorporated in the CDR thermal model • Added high emissivity black paint to TKR sidewalls • Lowers peak TKR temperature by radiatively coupling modules together • Raises ACD survival temperature and lowers TKR hot-case peak temperature by improving radiative coupling between the two • Connected TKR to Grid with 4 heat straps/module • Increases temperature gradient across the thermal joint • Improves thermal joint reliability compared to Delta-PDR thermal gasket design • Replaced outer ACD MLI blanket layer with germanium black kapton (FOSR before) • Preferred by subsystem, since MLI is unsupported • Marginally raises survival case temperatures • Increased total LAT power (w/o reservoirs) to 615 W (was 602W) • Total is still within the 650 W allocation • CAL and TKR power increased 21.6 W • Electronics power dropped 8.3 W • ACD power remained about the same • Net effect is to raise hot-case peak temperatures for the TKR and CAL • Added S-bend to VCHP transport section • Results in net drop in survival heater power needs • Reduces survival-case heat leak out of Grid • Increases anti-freeze radiator heater power • Improves flexibility for better compliance at integration • Increases transport capacity requirement on VCHP’s

  7. LAT Thermal Interface Design Changes Since Delta-PDR The following interface changes have been incorporated in the CDR thermal model • Increased Radiator area to 2.78 m2 but decreased efficiency by shortening it • Modified Radiator aspect ratio at request of Spectrum to accommodate solar arrays • This change results in slightly higher LAT hot-case temperatures • Finalized Radiator cut-outs • Added cut-outs for solar array launch locks • Increased size of cut-out for solar array mast • This change results in slightly higher LAT hot-case temperatures

  8. Trade Studies Since Delta-PDR • Solar Array interface for survival/cold cases • Delta-PDR total survival grid + anti freeze heater power calculated to be 171 watts (28.0 watts reservoirs)  191 W Total • Using the Spectrum PDR Solar Array, survival heater power increased to 244 W (28 W for reservoirs) • With no solar array, total survival heater power increased to 330 watts • Conclusion: using the Spectrum Astro PDR solar array in the LAT cold- and survival-case models was agreed as reasonable • Reservoir size reduction • Desire to maximize radiator area and temperature margins • Used Delta-PDR model to assure that smaller reservoir could totally close heat pipes for survival and provide adequate cold case control • Reduced size provides more condenser length • Conclusion: reduce reservoir size from Delta PDR volume of 288 cc to 75 cc. This produces a net gain of 100 mm in condenser length

  9. Thermal Systems Peer Review RFA Status RFA 13-Stowed Case Limiting LAT component –VCHP Reservoirs if heaters not activated

  10. Thermal Systems Peer Review RFA Status • RFA-14 Heater Flight sizing-at least 30% margin at minimum voltage • RFA-15 With all YS-90 Tracker sidewalls, peak tracker temperature at CDR • RFA-16 ACD limits –The ACD has already agreed to the lower(-40 C) limits of the Environmental specification • RFA-21 Backup test heater for flight anti-freeze heaters: not necessary due to control of environment in test • RFA-22 Maximum Tracker temperature with .03 MLI e* - Temperature rises to 24.75 C • RFA-25 Correlation of flight thermistors at unit level - will be done both for the Tracker and Calorimeter to establish proper limits at LAT level TVAC test • RFA-30 AO Effects on Germanium Black Kapton-See paper on AO from International SAMPE Technical conference, November 1996. Note that pristine Germanium Black kapton showed no effects from the AO. The ACD will have a scrim outer layer for the thermal blanket; it is recommended that the 2nd layer of the blanket also be germanium black kapton.

  11. Driving Thermal Design Requirements

  12. Thermal Model Details: LAT Dissipated Power • Dissipated power values are pulled directly from the LAT power budget held by the LAT System Engineer • All power allocations and geographical distribution is under CCB control LAT Dissipated Power Values Source: LAT-TD-00225-05 “A Summary of LAT Dissipated Power for Use in Thermal Design”, 16 Apr 2003

  13. Thermal Model Details: Electronics Box Dissipated Power LAT Dissipated Power Distribution in Special Electronics Boxes Source: LAT-TD-00225-04 “A Summary of LAT Dissipated Power for Use in Thermal Design”, 13 Mar 2003

  14. Environmental Temperature Limits

  15. Verification Test Temperatures • Component Level Testing Minimum test margins • 5 C margin from Operating to AT level • 5 C margin from AT to LAT PFQ level • LAT level Thermal Vacuum Test strategy • Drive all components to their ATP/PFQ level • Virtually impossible to achieve • Will most likely be limited by one or two components

  16. LAT Thermal Math Model and Status • TSS Model-Calculates radks and heat rates. • 252 Surfaces External, 454 Internal • 2787 Active Nodes External, 1436 Internal • Sinda Model. • Submodels. • ACD CDR model • Detailed TKR model • Reduced Cal model • Detailed Grid model • Updated X-LAT and Electronics model • Bus model includes solar arrays and SV • IRD array for hot case. • Cold case/survival uses Spectrum Astro PDR solar array. • Detailed radiator and heat pipes • 9812 nodes total • Heat pipe logic in VCHPs to predict gas front • Added VCHP heater control logic • Logic will be part of SIU control of thermal system Model status: the model is mature and includes all subsystem updates for CDR

  17. Thermal Model Details: Thermal Interfaces • Thermal interfaces to the Spacecraft • All specified in LAT IRD (433-IRD-0001) except cold-/survival-case solar array definition, which has been arrived at by mutual agreement between Spectrum, LAT, and the GLAST PO • Environmental parameters • PDR and Delta-PDR analysis shows that Beta = 0, pointed-mode is the LAT hot-case • Solar loading is per the LAT IRD • Sky-survey attitude and “noon roll” is based on an assumed slew rate of 9 degrees/min, max • Thermal design case parameters are tabulated on the following chart SC-LAT Thermal Interface Parameters

  18. Thermal Model Details: Design Case Details LAT Thermal Case Description Source: LAT-TD-00224-04 “LAT Thermal Design Parameters Summary”, 19 Mar 2003

  19. Temperature Predicts and Margins to Operating Limit • IRD Hot-Case peak temperatures predicts vs. “Real” Case Solar Array • Tracker: 29.4 C vs. 24.3 C • Calorimeter: 22.0 C vs. 16.8 C • Electronics: 36.0 C vs. 30.3 C Temperature Predicts for LAT Subsystems

  20. Sensitivity of Temperature Predictions

  21. Hot Case TKR Peak Temperature Gradient • Peak temperature gradient is along the heat transfer path to the top of a center TKR module • Key temperature gradients • Up TKR wall: 5.7 deg C • TKR—Grid thermal joint: 3.8 deg C • Top of Grid—DSHP at VCHP: ~7.7 deg C TKR Maximum Temperature Gradient in the LAT

  22. Hot Case Orbit: Beta 0, +Z Zenith, +X Sun Pointing sun Hot Case Environmental Orbit Loads Environmental Load on Radiators for Hot-Case Orbit

  23. Hot Case QMAP Hot Case QMAP Instrument Power 2068 W to space 2009 W orbital heating 615 W 42 W solar array heating 62 W orbital heating 83 W to space 235 W orbital heating 17 W from bus 252 W orbital heating 83.6 W solar array heating 83.5 W solar array heating 28 W from bus 27 W from bus 653 W to space 650 W to space 4.0 W to space 3.9 W to space Orbital heating Radiated to space Bus heating Bus heating VCHP reservoir-space VCHP reservoir Z 2.1 W solar 2.1 W solar Hot Operational Orbit Average Qmap Y

  24. Hot Case IRD Temperatures Predicted LAT Temperatures for Hot-Case Orbit

  25. Hot Case IRD Tracker Temperature Predicted TKR Temperature Showing Analysis Predict is Stabilizing Toward an Asymptote

  26. Hot Case IRD Radiator Temperatures

  27. Hot Case with “Real” PDR Solar Arrays

  28. Survival Orientation: +X Sun Pointing sun Survival Case Orbit Environmental Load on Radiators for Survival-Case Orbit

  29. Survival Case QMAP Survival Case QMAP 1568 W to space Make-up Heaters 1529 W orbital heating 73.8 W 21 W solar array heating 53 W orbital heating 69 W to space 15 W from bus 131 W orbital heating 130 W orbital heating 11 W from bus 11 W from bus 39 W solar array heating 40 W solar array heating 44.5 W heater power 43.5 W heater power 259 W to space 260 W to space 9.9 W to space Z 10.0 W to space Orbital heating Radiated to space Bus heating Bus heating VCHP reservoir Anti-freeze heaters VCHP reservoir 22 W heater power+solar 23 W heater power+solar Y Survival Orbit Average Qmap

  30. Survival Temperatures

  31. Survival Case Temperatures Predicted LAT Temperatures for Survival-Case Orbit

  32. Survival Case Radiator Temperatures Predicted Radiator Temperatures for Survival-Case Orbit

  33. Survival Heater Power • Survival heater power (orbit average) • Grid make-up heaters 69 W • VCHP anti-freeze heaters 89 W • X-LAT Plate heaters 0 W • Total heater power 158 W • Allocation: 220 Watts • Heater power margin: +62 W (43% margin)

  34. VCHP Reservoir Heater Power • Reservoir Heater Size • 3.5 W/Reservoir @ 27V = 42 W for 12 (100% duty cycle) • Survival minimum required power = 1.5 W/reservoir • Heaters sized at > 200% of required minimum • Reservoir Duty Cycles • Hot Case: 0% and 0 W • Cold Case: ~ 30%  13 W orbit-averaged power • Survival: 100%  42 W orbit-averaged power (heaters locked on while LAT is off)

  35. Cold Case Temperatures Predicted Temperatures for Cold-Case Orbit

  36. Cold Case Radiator Temperatures Predicted Radiator Temperatures for Cold-Case Orbit

  37. LAT Failure Analyses—Hot-Case Summary of Hot-Case Failure Analyses

  38. Hot Thermal Failure Analysis Results Summary • Change in peak temperatures • Failure of heat straps for center Bay increases peak Tracker temperature 4.3 o C

  39. LAT Failure Analyses—Cold/Survival Cases Change in peak temperatures and average power below Case 4-Reservoir temperaturesrise to 1050 C with both sets of heaters On Summary of Cold-/Survival-Case Failure Analyses

  40. Thermal Failure Analysis Results Summary • With one exception, all hot case failure scenarios led to a maximum temperature rise of less than 50 C • Failure of the XLAT #2 Heat Pipe Below the GASU causes large temperature rises in the GASU and TEM and TPS • GASU remains within operating limits • TEM and TPS rise above operating limit for “real” solar array • TEM and TPS would rise above ATP for IRD hot Case • These temperatures only seen when pipe under operating GASU section fails-can switch to B side of GASU to eliminate large rise • Heater failure cases do not require intervention, I.e. switch to backups • Heater power within limits • Temperatures within limits • Primary and secondary reservoir heaters cannot simultaneously be on in survival( 1050 C max)

  41. Integration and Test Flow LAT Integration and Test Flow

  42. LAT Thermal Balance/Thermal-Vacuum Tests • Test goals • Thermal-Balance • Verify that the LAT thermal control system is properly sized to keep maximum temperatures within mission limits, while demonstrating at least 30% control margin • Validate the LAT thermal control system control algorithms • Verify that the VCHP control effectively closes the radiator to when the LAT is off • Validate the LAT thermal model by correlating predicted and measured temperatures • Thermal-Vacuum • Verify the LAT’s ability to survive proto-qualification temperature levels at both the high and low end • Test for workmanship on hardware such as wiring harnesses, MLI, and cable support and strain-reliefs which will not have been fully verified at the subsystem level • Demonstrate that the LAT meets performance goals at temperature • Provide stable test environment to complete LAT surveys, as detailed in LAT-MD-00895, “LAT Instrument Survey Plan” • Configuration • The LAT instrument will be fully integrated but the SC solar arrays will not be installed • The LAT will be powered on and off during testing per the test procedure • The LAT will be oriented with the Z-axis parallel to the ground to allow all heat pipes to operate and the +X axis facing up • All MLI blanketing will be in its flight configuration for the duration of the 2 tests • The LAT will NOT be reconfigured after the thermal-balance test

  43. LAT Thermal Balance/Thermal-Vacuum Tests (cont) • Instrumentation • Thermocouples and RTD’s will be used to instrument the LAT and test chamber • LAT flight housekeeping instrumentation includes many thermistors and RTD’s. These will also be used for monitoring temperatures within the LAT • Specialized test equipment requirements • Chamber pressure of < 1 x 10-5 Torr • Chamber cold wall temperature of –180 oC to provide a cold sink for accumulation of contaminants • Thermally controlled surfaces in the chamber • 5 plates for ACD surfaces, each individually controlled • 2 plates for the radiators(one for each side), each individually controlled • 1 plate to simulate the bus, controlling the environment to the X-LAT Plate and the back of each radiator • Heat exchangers mounted on the +/– X sides of the LAT Grid, to increase ramp rate during transitions • LAT heat pipes will be leveled to within 0.2 degrees • 20 oC/hr max ramp rate • Facility capable of holding LAT stable to < 2 oC/hr rate of change (TBR) • Test profile • Dwell at high and low temps for 12 hours, min • Comprehensive Performance Tests conducted at select plateaus • Perform at ambient, during cold and hot soaks, and at return to ambient • Limited Performance Tests during transitions and plateaus • Check operating modes and monitor units for problems or intermittent operation

  44. LAT Thermal Balance/Thermal-Vacuum Test Profile LAT Thermal-Vacuum Test Profile Source: LAT-MD-01600-01, “LAT Thermal-Vacuum Test Plan,” March 2003

  45. LAT Cool Down During TVAC

  46. Issues • The X-LAT Plate to Electronics Box Interface needs better definition to properly evaluate the conductance across the interface • Current conductance assumption is 150 W/m2-deg C or 0.1 W/in2-deg C(poor dry joint) • High variability of tolerances between X-LAT plate and electronics boxes could lead to very poor overall joint thermal performance

  47. Summary • We are using a fully integrated thermal model for generating temperature predicts for CDR • The Radiator thermal design has been changed to incorporate modifications to the spacecraft interface • Predicts show that we meet all operating limits, with adequate margin, when using the IRD solar arrays • When using the expected “real” Spectrum Astro solar array, net flux to each radiator drops about 60 watts • With a “real” solar array, maximum temperatures drop about 5 C • Predicts show that we meet all operating limits, with adequate heater margin, when using the Spectrum solar arrays in the cold and survival cases

  48. Gamma-ray Large Area Space Telescope Appendix Thermal Analysis RFAs

  49. Peer Review RFAs

  50. Peer Review RFAs (Continued)

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