LAT Thermal Systems Analysis 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 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

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 On-Orbit Thermal Environment and LAT Process Power Survival Cold Hot Units Earth IR 208 265 W/m2 Earth Albedo 0.25 0.40 Solar Flux 1286 1419 LAT Process Power 535 612 W 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

3-D ISO OF RADIATOR, X-LAT, DSHP’S FROM RADIATOR TALK

LAT Thermal System Schematic Diagram LAT Thermal Schematic Diagram

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 612 W (was 602W) Total is still within the 650 W allocation CAL and TKR power increased 26 W Electronics power dropped 18 W ACD power increased 3 W 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

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

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

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

Thermal Systems Peer Review RFA Status RFA-14 Heater Flight sizing RFA-15 With all YS-90 Tracker sidewalls, peak tracker temperature is RFA-16 ACD limits RFA-21Backup flight heater for anti-freezeheaters: not necessary RFA-22 Maximum Tracker temperature with .03 MLI e* is RFA-25 Correlation of flight thermistors at unit level RFA-30 AO Effects on Germanium Black Kapton-See paper on AO from International SAMPE Technical conference, November 1996. UPDATE

Driving Thermal Design Requirements UPDATE

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 UPDATE LAT Dissipated Power Values Source: LAT-TD-00225-04 “A Summary of LAT Dissipated Power for Use in Thermal Design”, 13 Mar 2003

Thermal Model Details: Electronics Box Dissipated Power UPDATE 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

Environmental Temperature Limits

Verification Test Temperatures UPDATE

LAT Thermal Math Model and Status TSS Model-Calculates radks and heat rates XXX Surfaces YYY Active Nodes Sinda Model Submodels ACD CDR model Detailed TKR model Reduced Cal model Detailed Grid model X-LAT and Electronics model updated 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 ZZZ 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 interfaces understood. The electronics thermal model interface is the one deficiency, and is being worked on.

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

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

UPDATE quote all predicts including 5C margin Results Summary Hot-Case peak temperatures predicts Tracker Predict: 24 oC max Operating Limit: 30 oC Calorimeter: Predict: 16 oC max Operating Limit: 25 oC Electronics Predict: 28 oC max Operating Limit: 45 oC These are “raw predicts” and do not include 5 oC uncertainty UPDATE quote all predicts including 5C margin Temperature Predicts for LAT Subsystems

Temperature Predicts and Margins to Operating Limit Temperature predicts show that all subsystem components carry greater than 5 oC margin to their operating limit Minimum margin of 6 oC is for the center TKR module UPDATE Temperature Predicts for LAT Subsystems

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: 4.0 deg C Top of Grid—DSHP at VCHP: ~7.6 deg C UPDATE TKR Maximum Temperature Gradient in the LAT

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

Hot Operational Orbit Average Qmap Hot Case QMAP Hot Case QMAP 2072 W to space Instrument Power 2008 W orbital heating 612 W 46 W solar array heating UPDATE 64 W orbital heating 91 W to space 24 W from bus 235 W orbital heating 252 W orbital heating 83.5 W solar array heating 84 W solar array heating 30 W from bus 30 W from bus 652 W to space 648 W to space 3.9 W to space 3.9 W to space Z Orbital heating Radiated to space Bus heating VCHP reservoir Hot Operational Orbit Average Qmap Y

Predicted LAT Temperatures for Hot-Case Orbit Hot Case Temperatures UPDATE Predicted LAT Temperatures for Hot-Case Orbit

Hot Case Tracker Temperature UPDATE Predicted TKR Temperature Showing Analysis Predict is Stabilizing Toward an Aymptote

Hot Case Radiator Temperatures UPDATE

Hot Case with “Real” PDR Solar Arrays UPDATE

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

Survival Orbit Average Qmap Survival Case QMAP Survival Case QMAP 1569 W to space Make-up Heaters 1529 W orbital heating 61W 22 W solar array heating UPDATE 44 W orbital heating 63 W to space 13 W from bus 131 W orbital heating 130 W orbital heating 12 W from bus 12 W from bus 39 W solar array heating 38 W solar array heating 45.5 W heater power 45.5 W heater power 258 W to space 259 W to space Z 9.9 W to space 10.0 W to space Orbital heating Radiated to space Bus heating VCHP reservoir Anti-freeze heaters VCHP reservoir heaters 22 W heater power 23 W heater power Y Survival Orbit Average Qmap

Survival Temperatures UPDATE

Survival Case Temperatures UPDATE Predicted LAT Temperatures for Survival-Case Orbit

Survival Case Radiator Temperatures UPDATE Predicted Radiator Temperatures for Survival-Case Orbit

UPDATE Survival Heater Power Survival heater power (orbit average) Grid make-up heaters 61 W VCHP anti-freeze heaters 91 W X-LAT Plate heaters 0 W Total heater power 152 W Allocation: 220 Watts Heater power margin: +68 W (45% margin) UPDATE

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) UPDATE

Cold Case Temperatures UPDATE Predicted Temperatures for Cold-Case Orbit

Cold Case Radiator Temperatures UPDATE Predicted Radiator Temperatures for Cold-Case Orbit

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

LAT Failure Analyses—Cold/Survival Cases Summary of Cold-/Survival-Case Failure Analyses

Thermal Failure Analysis Results Summary TABLE OF PEAK TEMPS AND TEMP CHANGES FOR FAILURE CASES RUN UPDATE

Thermal Failure Analysis Results Summary UPDATE

LAT Thermal Analysis Summary UPDATE

Integration and Test Flow UPDATE LAT Integration and Test Flow

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

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

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

LAT Thermal Verification Test Temperatures Thermal Test Levels Test strategy Drive components to PFQ limit for LAT, defined in the MAR as Operating limit +/- 10 oC, min Minimum test margins 5 C margin from Operating to AT level 5 C margin from AT to LAT PFQ level UPDATE LAT Thermal Verification Test Temperatures Source: LAT-SS-00778-01 “LAT Environmental Specification,” March 2003

UPDATE Summary Summary We are working towards completing and using a fully integrated thermal model of the CDR design 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 UPDATE