Document: LAT-PR-01967Section 8.C Thermal Design1 GLAST LAT ProjectCDR/CD-3 Review, May Jeff Wang LMCO LAT Thermal Engineer Gamma-ray Large Area Space Telescope LAT Thermal Systems Analysis

Document: LAT-PR-01967Section 8.C Thermal Design2 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design3 GLAST LAT ProjectCDR/CD-3 Review, May 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 m 2 –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 On-Orbit Thermal Environment and LAT Process Power SurvivalColdHotUnits Earth IR W/m 2 Earth Albedo Solar Flux W/m 2 LAT Process Power W MLI thermal shielding surrounding ACD, Grid Box, Electronics X-LAT Heat Pipes shunt electronics power to Radiators LAT Thermal Overview Active VCHP control allows for variable Radiator area to maintain constant interface temp to LAT Down Spout Heat Pipes connect Grid to Radiators

Document: LAT-PR-01967Section 8.C Thermal Design4 GLAST LAT ProjectCDR/CD-3 Review, May Downspout and X-LAT Heat Pipes

Document: LAT-PR-01967Section 8.C Thermal Design5 GLAST LAT ProjectCDR/CD-3 Review, May LAT Thermal System Schematic Diagram LAT Thermal Schematic Diagram

Document: LAT-PR-01967Section 8.C Thermal Design6 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design7 GLAST LAT ProjectCDR/CD-3 Review, May 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 m 2 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

Document: LAT-PR-01967Section 8.C Thermal Design8 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design9 GLAST LAT ProjectCDR/CD-3 Review, May Thermal Systems Peer Review RFA Status RFA 13-Stowed Case Limiting LAT component –VCHP Reservoirs if heaters not activated

Document: LAT-PR-01967Section 8.C Thermal Design10 GLAST LAT ProjectCDR/CD-3 Review, May 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 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 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 2 nd layer of the blanket also be germanium black kapton.

Document: LAT-PR-01967Section 8.C Thermal Design11 GLAST LAT ProjectCDR/CD-3 Review, May Driving Thermal Design Requirements

Document: LAT-PR-01967Section 8.C Thermal Design12 GLAST LAT ProjectCDR/CD-3 Review, May 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 “A Summary of LAT Dissipated Power for Use in Thermal Design”, 16 Apr 2003

Document: LAT-PR-01967Section 8.C Thermal Design13 GLAST LAT ProjectCDR/CD-3 Review, May Thermal Model Details: Electronics Box Dissipated Power Source: LAT-TD “A Summary of LAT Dissipated Power for Use in Thermal Design”, 13 Mar 2003 LAT Dissipated Power Distribution in Special Electronics Boxes

Document: LAT-PR-01967Section 8.C Thermal Design14 GLAST LAT ProjectCDR/CD-3 Review, May Environmental Temperature Limits

Document: LAT-PR-01967Section 8.C Thermal Design15 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design16 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design17 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design18 GLAST LAT ProjectCDR/CD-3 Review, May Thermal Model Details: Design Case Details Source: LAT-TD “LAT Thermal Design Parameters Summary”, 19 Mar 2003 LAT Thermal Case Description

Document: LAT-PR-01967Section 8.C Thermal Design19 GLAST LAT ProjectCDR/CD-3 Review, May Temperature Predicts and Margins to Operating Limit Temperature Predicts for LAT Subsystems IRD Hot-Case peak temperatures predicts vs. “Real” Case Solar Array –Tracker: 29.4 C vs C –Calorimeter: 22.0 C vs C –Electronics: 36.0 C vs C

Document: LAT-PR-01967Section 8.C Thermal Design20 GLAST LAT ProjectCDR/CD-3 Review, May Sensitivity of Temperature Predictions

Document: LAT-PR-01967Section 8.C Thermal Design21 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design22 GLAST LAT ProjectCDR/CD-3 Review, May Hot Case Environmental Orbit Loads Hot Case Orbit: Beta 0, +Z Zenith, +X Sun Pointing sun Environmental Load on Radiators for Hot-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design23 GLAST LAT ProjectCDR/CD-3 Review, May W orbital heating 252 W orbital heating 235 W orbital heating 83.5 W solar array heating 83.6 W solar array heating 653 W to space 650 W to space 2068 W to space Instrument Power 615 W 17 W from bus 42 W solar array heating Y Z 27 W from bus 4.0 W to space 3.9 W to space Hot Case QMAP Orbital heating Radiated to space Bus heating VCHP reservoir-space VCHP reservoir 62 W orbital heating 83 W to space Hot Case QMAP Hot Operational Orbit Average Qmap 28 W from bus 2.1 W solar

Document: LAT-PR-01967Section 8.C Thermal Design24 GLAST LAT ProjectCDR/CD-3 Review, May Hot Case IRD Temperatures Predicted LAT Temperatures for Hot-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design25 GLAST LAT ProjectCDR/CD-3 Review, May Hot Case IRD Tracker Temperature Predicted TKR Temperature Showing Analysis Predict is Stabilizing Toward an Asymptote

Document: LAT-PR-01967Section 8.C Thermal Design26 GLAST LAT ProjectCDR/CD-3 Review, May Hot Case IRD Radiator Temperatures

Document: LAT-PR-01967Section 8.C Thermal Design27 GLAST LAT ProjectCDR/CD-3 Review, May Hot Case with “Real” PDR Solar Arrays

Document: LAT-PR-01967Section 8.C Thermal Design28 GLAST LAT ProjectCDR/CD-3 Review, May Survival Case Orbit sun Survival Orientation: +X Sun Pointing Environmental Load on Radiators for Survival-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design29 GLAST LAT ProjectCDR/CD-3 Review, May Survival Case QMAP 1529 W orbital heating 130 W orbital heating 40 W solar array heating 259 W to space 1568 W to space Make-up Heaters 73.8 W 15 W from bus 21 W solar array heating 11 W from bus 9.9 W to space 43.5 W heater power 44.5 W heater power 69 W to space 53 W orbital heating 22 W heater power+solar Survival Case QMAP Y Z Survival Orbit Average Qmap Orbital heating Radiated to space Bus heating VCHP reservoir Anti-freeze heaters VCHP reservoir 131 W orbital heating 39 W solar array heating 260 W to space 10.0 W to space 23 W heater power+solar 11 W from bus

Document: LAT-PR-01967Section 8.C Thermal Design30 GLAST LAT ProjectCDR/CD-3 Review, May Survival Temperatures

Document: LAT-PR-01967Section 8.C Thermal Design31 GLAST LAT ProjectCDR/CD-3 Review, May Survival Case Temperatures Predicted LAT Temperatures for Survival-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design32 GLAST LAT ProjectCDR/CD-3 Review, May Survival Case Radiator Temperatures Predicted Radiator Temperatures for Survival-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design33 GLAST LAT ProjectCDR/CD-3 Review, May Survival Heater Power Survival heater power (orbit average) Grid make-up heaters69 W VCHP anti-freeze heaters89 W X-LAT Plate heaters0 W Total heater power158 W Allocation:220 Watts Heater power margin:+62 W (43% margin)

Document: LAT-PR-01967Section 8.C Thermal Design34 GLAST LAT ProjectCDR/CD-3 Review, May VCHP Reservoir Heater Power Reservoir Heater Size –3.5 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)

Document: LAT-PR-01967Section 8.C Thermal Design35 GLAST LAT ProjectCDR/CD-3 Review, May Cold Case Temperatures Predicted Temperatures for Cold-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design36 GLAST LAT ProjectCDR/CD-3 Review, May Cold Case Radiator Temperatures Predicted Radiator Temperatures for Cold-Case Orbit

Document: LAT-PR-01967Section 8.C Thermal Design37 GLAST LAT ProjectCDR/CD-3 Review, May LAT Failure Analyses—Hot-Case Summary of Hot-Case Failure Analyses

Document: LAT-PR-01967Section 8.C Thermal Design38 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design39 GLAST LAT ProjectCDR/CD-3 Review, May LAT Failure Analyses—Cold/Survival Cases Summary of Cold-/Survival-Case Failure Analyses Case 4-Reservoir temperatures rise to C with both sets of heaters On Change in peak temperatures and average power below

Document: LAT-PR-01967Section 8.C Thermal Design40 GLAST LAT ProjectCDR/CD-3 Review, May Thermal Failure Analysis Results Summary With one exception, all hot case failure scenarios led to a maximum temperature rise of less than 5 0 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( C max)

Document: LAT-PR-01967Section 8.C Thermal Design41 GLAST LAT ProjectCDR/CD-3 Review, May Integration and Test Flow LAT Integration and Test Flow

Document: LAT-PR-01967Section 8.C Thermal Design42 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design43 GLAST LAT ProjectCDR/CD-3 Review, May 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 Torr –Chamber cold wall temperature of –180 o C 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 o C/hr max ramp rate –Facility capable of holding LAT stable to < 2 o C/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

Document: LAT-PR-01967Section 8.C Thermal Design44 GLAST LAT ProjectCDR/CD-3 Review, May LAT Thermal Balance/Thermal-Vacuum Test Profile LAT Thermal-Vacuum Test Profile Source: LAT-MD , “LAT Thermal-Vacuum Test Plan,” March 2003

Document: LAT-PR-01967Section 8.C Thermal Design45 GLAST LAT ProjectCDR/CD-3 Review, May LAT Cool Down During TVAC

Document: LAT-PR-01967Section 8.C Thermal Design46 GLAST LAT ProjectCDR/CD-3 Review, May 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/m 2 -deg C or 0.1 W/in 2 -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

Document: LAT-PR-01967Section 8.C Thermal Design47 GLAST LAT ProjectCDR/CD-3 Review, May 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

Document: LAT-PR-01967Section 8.C Thermal Design48 GLAST LAT ProjectCDR/CD-3 Review, May Gamma-ray Large Area Space Telescope Appendix Thermal Analysis RFAs

Document: LAT-PR-01967Section 8.C Thermal Design49 GLAST LAT ProjectCDR/CD-3 Review, May Peer Review RFAs

Document: LAT-PR-01967Section 8.C Thermal Design50 GLAST LAT ProjectCDR/CD-3 Review, May Peer Review RFAs (Continued)