LAT Requirements Verification in TVAC LAT Mission Thermal Requirements are provided in four documents: 433-MAR-0001, “Mission Assurance Requirements”, Sections 4.6, 10.4 LAT-SS-00778, “LAT Environmental Specification”, Section 11.1,2,3 LAT-MD-00408, “LAT Program Instrument Performance Verification Plan”, Sections 5, 7.1.1.8 LAT-SS-00010-02, “LAT Performance Specification – Level II (B)”, Section 5.3.11.1,2 Requirements verification by individual test is summarized in Test Segment Chart and detailed in the LAT TVAC Test Plan.

LAT Requirements Verification LAT Thermal Environmental Parameter Surv. Cold-Case Nom Hot-Case Units Source Earth IR on any exposed surface 208 265 W/m2 IRD 3.2.3.5, Table 3-3 Earth Albedo on any exposed surfaces 0.25 0.4   Solar Flux on surfaces exposed to +X direction 1286 1419 Solar flux due to 1 deg glancing view of the sun on +/- Y surfaces 6 SPS 3.4.5.1 Orbit-average absorbed solar flux on one Radiator due to re-pointing 27 W

LAT Requirements Verification LAT Environmental Test Loads and Durations

LAT Thermal Vacuum Testing Timeline

Thermal Vacuum Test Segments Individual Test Segments are Conducted in the Following Order According to LAT Document [TBD] “LAT TVAC Test Procedures” Chamber Pump Down Bakeout Hot Operational Thermal Balance Hot Operational Thermal Control System Hot Operational Peak Power Hot Performance Cold Survival Thermal Balance Cold Performance Cold Operational Thermal Balance Cold Operational Thermal Control System Thermal Cycling Chamber Recovery During and between certain above tests, LAT electrical performance tests will be conducted according to the LAT “Electrical Performance Test Procedure"

Chamber Pump Down Electrical Performance Tests, chamber door open. Pump down according to NRL procedures to <1.E-05 Torr Activate LAT power buses, but LAT is powered OFF. Chamber shroud cool down according to NRL procedures. Adjust simulated environmental temperature hardware to maintain LAT assembly between 20 and 40 degC.

Bakeout Adjust simulated environmental temperature hardware to maintain LAT assembly at 45 degC Monitor out-gassing with Thermal Quartz Crystal Microbalance (TQCM) according to the LAT Contamination Control Plan Duration of bakeout according to TQCM criteria in LAT Contamination Control Plan

Hot Operational Thermal Balance Simulated environmental temperature hardware adjusted to provide hot case end-of-life (EOL) environmental heat loads. Thermal balance is attained when there is less than a 5% energy imbalance in the LAT instrument. The RIT is expected to stabilize below +15 degC without TCS control. Science verification and calibration tests are performed (power dissipation is unaltered). Thermal data used to correlate the LAT systems level Thermal Math Model, which provides flight temperature predictions.

Hot Operational Thermal Control System Hot TCS Testing consists of three tests: RIT control using primary reservoir heaters and symmetric orbit average load. Only primary reservoir heaters enabled (redundant heaters are controlled by B-side SIU, so this is standard). Primary and redundant radiator survival (antifreeze) heaters are enabled, but are expected to remain off. RIT initial set point same as that achieved previously in hot operational thermal balance. Demonstrate RIT control by incrementally increasing RIT set point to +15 degC and then lowering back to original level. Peak power. Increase LAT power to peak levels (706W) for 10 minutes or until a steady state has been achieved at the discrition of the thermal engineer. Monitor LAT temperatures to assure they remain within limits RIT control using redundant reservoir heaters at nominal power with transient environmental loading Configure LAT with only redundant reservoir heaters enabled. Control radiator simulated environmental temperature hardware to follow hot case temperature profiles. Demonstrate RIT control by incrementally increasing RIT set point to +15 degC and then lowering back to original set level. Verify ability of TCS to maintain RIT stable within +/- 7 degC under transient environmental radiator loads.

Radiator Sink Transient Temperatures – Hot Case

Hot Performance Simulated environmental temperature hardware adjusted “until as many LAT temperatures as feasible are 10 degC above their predicted operating limits.” This will be the hot proto-qualification temperature limit. Thermal stability is attained when certain monitored temperatures* are within 3 degC [TBD] of target/goals. After LAT temperatures are stable, execute a LAT Power-On/Off/On sequence according to LAT Electrical Test Procedure. * Note: “Certain monitored temperatures” are a set of temperature sensors that represent the complete temperature distribution within the LAT.

Cold Survival Thermal Balance Simulated environmental temperature hardware adjusted to provide environment for cold survival case. Transition according to LAT TVAC Test Procedure. LAT is powered off after LPT. Primary and redundant survival (Grid and radiator) heater circuits are enabled. Primary and redundant reservoir heater circuits are enabled. After reaching primary set point temperature, the primary survival heaters will cycle and the redundant heaters will remain off since the redundant temperature set point is set below that of the primary Redundant reservoir heater is thermostatically controlled and will turn off when temperature increases above +15 degC. Primary heater will maintain reservoir at near +40 degC at 100% duty cycle. Thermal balance attained when there is less than a 5% energy imbalance in the LAT. RIT is expected to stabilize near - 6 degC. Following thermal balance, redundant Grid and radiator survival heater circuits are enabled and primary circuits are disabled, and environmental temperatures are decreased slightly until redundant thermostats engage the redundant heaters. EGSE must be designed for this function and also to override reservoir heater circuit enabling.

Cold Performance Simulated environmental temperature hardware is adjusted until “as many LAT temperatures as feasible are 10 degC below their predicted operating limits.” This will be the cold proto-qualification temperature limit. Not practical at cold end, since cold performance and operational limits are below cold survival limit. Thermal stability is attained when certain monitored temperatures [TBD] are within 3 degC [TBD] of target/goals. After LAT temperatures are stable, execute a LAT Power-On/Off/On sequence according to LAT Electrical Test Procedure.

Cold Operational Thermal Balance Simulated environmental temperature hardware adjusted to provide cold case beginning-of-life (BOL) environmental heat loads. Thermal balance is attained when there is less than a 5% energy imbalance in the LAT instrument. The RIT is expected to stabilize below -10 degC without TCS control. Science verification and calibration tests are performed (power dissipation is unaltered) Thermal data used to correlate the LAT systems level Thermal Math Model, which provides flight temperature predictions.

Cold Operational Thermal Control System Cold TCS Testing consists of three tests: RIT control using primary reservoir heaters and symmetric orbit average load. Only primary reservoir heaters enabled (redundant heaters are controlled by B-side SIU, so this is standard). Primary and redundant radiator survival (antifreeze) heaters are enabled, but are expected to remain off. RIT initial set point same as that achieved previously in cold operational thermal balance. Incrementally increase RIT set point to +15 degC and then lower back to original level. RIT control using redundant reservoir heaters at nominal power with transient environmental loading Configure LAT with only redundant reservoir heater enabled. Control radiator simulated environmental temperature hardware to follow cold case temperature profiles. Demonstrate RIT control by incrementally increasing RIT set point to +15 degC and then lowering back to original set point. Verify ability of TCS to maintain RIT stable within +/- 7 degC under transient environmental loads. TCS Parameter Upload. Enabling antifreeze protection at higher temperatures. Changing reservoir heater control band. Disabling an individual VCHP. Rejection of impossible or conflicting parameters.

Radiator Sink Transient Temperatures

Thermal Cycling A total of four thermal cycles will be performed consisting of four hot plateau four cold plateau eight transitions At each plateau, electrical performance testing according to timeline and LAT Electrical Test Procedure

Chamber Recovery Chamber recovery according to NRL Procedures Return to ambient temperature simulated environmental temperature hardware adjusted to maintain LAT assembly between 22 and 30 degC. RIT set point temperature adjusted accordingly. when ambient temperature achieved, LAT is powered off and power circuits disabled. all GSE power circuits disabled. Return to ambient pressure Check room humidity to be in proper range before opening vacuum chamber door.

LAT TVAC Test Segments

TVAC LAT Cool Down Comparison Cool Down Scenarios During LAT TVAC Cycling

Simulated Environmental Temperature – Cal Rod Concept “Picture Frame” baffles; polished aluminum with holes for Cal Rod sockets Height of ACD Height of radiator 6” 6” – 8” Support structure, low e with heaters or blanketed; 15” – 20” from radiator Width of radiator

LAT TVAC Personnel Requirements Category Description Test Conductor (alternate between Cat 2 and Cat 4 or 5) Thermal Engineer Chamber/Facility Engineer LAT Operations/Systems Engineer LAT Electrical/Performance Scientist LAT Software Engineer Subsystem Specialist, ACD Subsystem Specialist, TKR Subsystem Specialist, CAL Subsystem Specialist, E-Box/Cabling 30 day test x 3 shifts/day = 90 shifts Cat 1 – 3: all shifts Cat 4: all shifts initially, part time during cycling Cat 5: all shifts initially, then as necessary, always during electrical performance tests Cat 6: all shifts initially, then as necessary Cat 7 – 10: all shifts initially, then during electrical performance tests Estimated total effort: 400 shifts x 8 hr/shift = 3200 hrs