1. 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,
LAT-SS , “LAT Performance Specification – Level II (B)”, Section ,2
Requirements verification by individual test is summarized in Test Segment Chart and detailed in the LAT TVAC Test Plan.

2. 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 , 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
Orbit-average absorbed solar flux on one Radiator due to re-pointing 27 W

3. LAT Requirements Verification
LAT Environmental Test Loads and Durations

4. LAT Thermal Vacuum Testing Timeline

5. 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"

6. 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.

7. 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

8. 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.

9. 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.

10. Radiator Sink Transient Temperatures – Hot Case

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. Radiator Sink Transient Temperatures

17. 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

18. 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.

19. LAT TVAC Test Segments

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

21. 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

22. 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