1. ROCSAT-2 Topic: Thermal Analysis Results - ISUAL Scientific Payload (with STR and IRU) Jeng-Der Huang ( 黃正德 )

2. ROCSAT-2 Contents  Thermal Design Description  Configuration  Power Dissipation  Thermal Analysis Results  Thermal Analysis Results Discussion

3. ROCSAT-2 ISUAL, STR and IRU Thermal Design Description  ISUAL, STR (Star Tracker) and IRU (Inertial Reference Unit) are thermal isolated from the payload platform to reduce the platform’s thermal distortion.  ISUAL, STR and IRU have the independent thermal control to keep the temperatures within their limits.  Thermal control devices such as the radiator, MLI and heater are used to maintain the temperatures within their operating/non- operating limits.

4. ROCSAT-2 Configuration STR CCD Imager Array Photometer Spectrophotometer IRU AEP

5. ROCSAT-2  Nominal hot (operating EOL) Power Dissipation

6. ROCSAT-2  Nominal cold (stand-by BOL) Power Dissipation (Continued)

7. ROCSAT-2  ASH mode Power Dissipation (Continued)

8. ROCSAT-2  Radiator area requirement Thermal Analysis Results

9. ROCSAT-2 Radiator STR IRU Radiator Radiator Locations Bus units

10. ROCSAT-2 Array Photometer CCD Imager Spectrophotometer AEP Radiator Radiator Locations (Continued) ISUAL units

11. ROCSAT-2  Orbit averaged heater power requirement Thermal Analysis Results (Continued)

12. ROCSAT-2 âPredicted temperatures for nominal hot case Thermal Analysis Results (Continued)  The actual minimum operating temperature limit for IRU is 10 o C, but 20 o C is an optimal lower limit.  The heater load margin (25% excess control authority) instead of heater temperature margin (6 o C above the temperature limit) is applied. * The STR radiator sizing is based on 14 o C with considering thermal uncertainty margin of 8 o C although its predicted margin is only 1.8 o C.

13. ROCSAT-2 âPredicted temperature for nominal cold case (stand-by mode) Thermal Analysis Results (Continued)  The actual minimum operating temperature limit for IRU is 10 o C, but 20 o C is an optimal lower limit.  The heater load margin (25% excess control authority) instead of heater temperature margin (6 o C above the temperature limit) is applied. * The STR radiator sizing is based on 14 o C with considering thermal uncertainty margin of 8 o C although its predicted margin is only 1.8 o C.

14. ROCSAT-2 âPredicted temperature for ASH case Thermal Analysis Results (Continued)  The actual minimum operating temperature limit for IRU is 10 o C, but 20 o C is an optimal lower limit.  The heater load margin (25% excess control authority) instead of heater temperature margin (6 o C above the temperature limit) is applied.

15. ROCSAT-2 Thermal Analysis Results (Continued)

16. ROCSAT-2 Thermal Analysis Results (Continued)

17. ROCSAT-2 Thermal Analysis Results (Continued)

18. ROCSAT-2 Thermal Analysis Results (Continued)

19. ROCSAT-2 Thermal Analysis Results (Continued)

20. ROCSAT-2 Thermal Analysis Results (Continued)

21. ROCSAT-2  ISUAL Portion: âThree ISUAL units (including Spectrophotometer, Array Photometer, and CCD Imager) were put together on a stack on the top of PIP and the other unit - AEP inside Bus during the SDR. However, all units have been moved to the top of PIP separately during the PDR. âThe total radiator areas of ISUAL have changed from 0.059 m 2 for SDR to 0.136 m 2 (include AEP) for PDR due to the configuration and the uncertainty margin changes (from 11 o C to 8 o C). âThe heater margin was changed from 10 o C to 6 o C in the PDR thermal analysis. Besides, the change in ISUAL layout. The total heater power requirements are effectively reduced as follows: SDR PDR åNominal imaging: 0.0 Watt 0.0 Watt åNominal standby: 0.0 Watt 0.0 Watt åASH: 12.6 Watt 2.7 Watt Thermal Analysis Results Discussion

22. ROCSAT-2 Thermal Analysis Results Discussion (Continued) âBoth worst hot and cold predicted temperatures of ISUAL are within the maximum and minimum operating/non-operating limits with proper margins by applying radiators and heaters. âThere is no heater power required to keep the ISUAL above the minimum temperature limits in nominal operation. For ASH mode, two ISUAL units, i.e., CCD Imager and Array Photometer, are controlled by heaters to maintain the minimum temperatures above their non-operating lower limits with proper margin. âThe built-in survival heaters of Array Photometer, Spectrophotometer and CCD Imager are strongly suggested for temperature control.

23. ROCSAT-2 Thermal Analysis Results Discussion (Continued)  IRU and STR: âThe IRU and STR radiators have been changed respectively from 0.092 m 2 and 0.053 m 2 for SDR to 0.121 m 2 and 0.062 m 2 for PDR due to the changes of configurations, temperature limits, and the uncertainty margin. âMore heater powers are required to maintain the IRU and STR units within the narrow allowable temperature ranges (20 o C ~ 30 o C for IRU and 18 o C ~ 22 o C for STR) in nominal mode, although the heater margin was changed from 10 o C to 6 o C in the PDR thermal analysis. âBoth worst hot and cold predicted temperatures of IRU and STR are all within their maximum and minimum operating/non-operating limits with proper margins by applying radiators and heaters. âDue to the narrow operating temperature ranges, IRU and STR should be precisely controlled by proper radiator and heater sizing in nominal operation.

24. ROCSAT-2 ISUAL Thermal Issues  ISUAL units are originally designed to be thermally conducting to the PIP. However, the thermal interface constraint of thermal isolation between the ISUAL and the PIP may force the ISUAL to change its interior or interface design. In the ISUAL SDR meeting (6/7 - 6/9 in NSPO), UCB (ISUAL Prime Contractor) considered it would be a great hardship to do any design modification because of tight budget and schedule.  ISUAL detailed thermal analysis can not be started without the knowledge of operating/non-operating temperature limits and thermal properties of critical parts (such as CCD, optical lenses, parts with high voltage and high dissipation, etc.) as well as heat transfer paths inside the units. Currently, only averaged temperature for each ISUAL unit is predicted.  ISUAL thermal verification (by analysis and test) is hard to be defined and planned.