2003-01-2459 Thermal Vacuum Test Performance of the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Variable Conductance Heat Pipe Assembly Paul E. Cleveland Energy Solutions International, L.L.C. Matthew T. Buchko Swales Aerospace, Inc. Richard A. Stavely NASA / Goddard Space Flight Center Copyright 0 2003 SAE International ABSTRACT Servicing Mission 4 (SM-4) is currently scheduled for 2005. During one of the five EVA days, the crew will The Variable Conductance Heat Pipe (VCHP) Assembly replace the Wide Field Planetary Camera II (WFPCII) of the HST Wide Field Camera 3 was subjected to with the Wide Field Camera 3 (WFC3). The HST slot for thermal vacuum (TN) environmental testing. The test these instruments is the “-V3 Radial Instrument” program included both maximum and minimum position. environments as well as simulated on-orbit cycling. Elements of the VCHP assembly included a VCHP, an The WFC3 contains both Ultraviolet and Infrared optical bench cold plate with an imbedded constant detectors. Due to the differing thermal requirements for conductance heat pipe, and a VCHP reservoir radiator these items and their associated assemblies, the WFC3 with a proportionally controlled heater. contains several thermal subsystems within the instrument enclosure. Figure 1 shows the instrument The purpose of the test was to characterize and enclosure and identifies some of the thermal control demonstrate the assembly’s ability to control the hardware. (The instrument optical bench has been temperature of the cold plate, which provides a stable removed for clarity). One of these subsystems is the thermal environment for the instrument‘s optical bench. Variable Conductance Heat Pipe (VCHP) assembly. This paper discusses the VCHP Assembly control Figure 1 WFC3 Enclosure with VCHP Assembly performance and control authority during the dynamic hot and cold 90-minute orbit cycling test phases. Electronics (MEB) INTRODUCTION Main (Detector) Radiator with The Hubble Space Telescope (HST) is one of the external National Aeronautics and Space Administration’s (NASA) Spreadermeader Heat Pipe network premier astronomical observatories. A unique design (U-Pipe on IR side feature of the spacecraft is its capacity to be serviced not shown) and refurbished on-orbit. Repairs to the HST are made during events called Servicing Missions (SM). The SM Cold Plate with consists of several phases that include: shuttle launch, Embedded CCHP inside WFC3 Enclosure ascent, rendezvous with HST, grapple, Extra Vehicular Activity (EVA) servicing, redeployment of the HST, shuttle entry and landing. The purpose of a SM is to upgrade the HST scientific capabilities and to repair or replace failed equipment. The benefit of the SM is to As a radial instrument, the WFC3 sees an HST internal enhance the scientific capability of the HST and to thermal environment that ranges from 13°C to 20°C. extend its operational lifetime to a decade or more. This environment, however, is too warm for the IR L '. ' , ' Detector components. The preferred temperature for the TEST OVERVIEW IR optical components is 0°C. The instrument Optical Bench Assembly (OBA), which houses the IR optics, is Figure 2 shows the overall test profile. Table 1 identifies thus cooled to 0°C by placing a radiative heat sink or the various test phases. As shown, there were sixteen Cold Plate under the OBA. The Cold Plate is maintained discreet cases. This paper addresses Case 5, "Cold at -5°C. The Cold Plate, in turn, is coupled to the Cycling", and Case 10, "Hot Cycling". These two cases external radiator. Since the radiator orbital temperature were of particular interest because they bracket the variations do not provide a stable heat sink, a variable dynamic operational requirements of the assembly from thermal coupling to the radiator is required. The actively a power and an environmental perspective. controlled VCHP Assembly provides this variable coupling. Table 1: Summary of Thermal Vacuum Test Phases The VCHP assembly consists of the Optical Bench Cold Phase Plate (OBCP), which contains an imbedded constant conductance heat pipe (CCHP); a variable conductance heat pipe; and a VCHP reservoir radiator (offset and thermally decoupled from the main WFC3 external radiator). The reservoir radiator, which regulates the reservoir gas temperature, uses a proportionally I 4 ]Minimum Radiator TemDerature / CaDacitv Test I controlled heater system. The VCHP condenser utilizes I 5 kold Cvclina I the main WFC3 external radiator to reject its heat to 6 Cold Decontamination space. The OBCP and the OBA are jointly wrapped in a 7 Hot Balance Multi Layer Insulation (MLI) enclosure. 8 Maximum Radiator Temperature / Capacity Test The primary challenge for the VCHP assembly is to 9 IPost Insertion Hot Case maintain the OBCP at -5°C k 2°C for various heat loads 10 lHot Cvclina while subject to a 90-minute orbit cycling environment 11 Return to Ambient which ranges from 0°C to -143°C. 12 Remove all MLI 13 Pumpdown This paper discusses the VCHP Assembly control 14 Bakeout performance during the dynamic hot and cold, 90-minute 15 Contamination Certification orbit cycling test phases. These phases are of particular I I interest because they demonstrate the control authority 16 IReturn to Ambient of the assembly. The test was conducted in Chamber #237 at the NASNGoddard Space Flight Center (GSFC). It lasted approximately fourteen days, from 5-28-02 to 6- 10-02. Figure 2: VCHP TNT est Profile Note. Temperature profile represents the radiator simulator cryopanel. 100 __ --- 7-! -- 75 50 25 0- 0 E 5 -25 B c" -50 -75 -100 -1 25 -1 50 t . . , , . . . . , . , . . . . .I.' , ' . . .', . .'. . , '. . . , ' , .', 1 . .' . . I 0 25 50 75 100 125 150 175 200 225 Time -Hours ' ,I ' TEST OBJECTIVES hardware, and Ground Support Equipment (GSE). Major elements included: Table 2 lists the test objectives for the entire test. Each objective served to characterize the VCHP performance The flight optical bench cold plate with an integral and capacity for a specific flight-like environment. CCHP. All flight thermal control hardware - heaters, FETs and thermistors were installed. See Figure 5. Table 2: VCHP Test Objectives The 25-watt, dual-element flight heater was controlled via the test power supplies in order to Test Objectives provide the appropriate heat load. The power supplies had the capability to provide both Demonstrate adequate system performance in hot balance condition. (Hot flight environment). temperature control and heater flux control. Maximum heat load. Maintain svstem cold-date at The flight VCHP system including flight thermistors. -5°C k2"C. See Figure 6. Demonstrate adequate system performance in cold The flight reservoir radiator with flight heaters, FETs, balance condition. (Cold flight environment). and thermistors. A GSE set-point commandable Minimum heat load. Maintain system cold-plate at proportional controller drove the 10 -watt heater -5°C k2"C. system, which consisted of two 5-watt, dual-element Provide sufficient information at the cold and hot heaters. The dual elements provide redundancy. balance conditions to allow thermal model correlation. Demonstrate ability of VCHP heater to shutdown Figure 3. Test Configuration in Chamber 237 the condenser in the cold case. Per GEVS, there should be at least 30% heater power margin. Demonstrate control authority of system when subjected to a simulated cold worst-case orbit- varying sink i.e., time varying sink. Maintain system cold-plate at -5°C k2"C. Demonstrate control authority of system when subjected to a simulated hot worst-case orbit- varying sink i.e., time varying sink. Maintain system cold-plate at -5°C k2"C. Measure temperature gradient along VCHP condenser during cold and hot cases. Characterize joint and interface conductances at key heat transfer paths along the system. (Cold Plate to CCHP, CCHP to VCHP saddle assembly, condenser to system radiator, reservoir to reservoir- radiator, reservoir-radiatort o system radiator). Characterize throughput conductance i.e., end-to- end conductance, of the system. Demonstrate hot start capability of the thermal system. Figure 4 Test Layout in Chamber 237. Demonstrate cold start capability of thermal system at cold mission extremes as well as at survival limits. Verify proper workmanship and operation of all components when integrated as a system. Conduct a maximum radiator temperature / CaDabilitv test. Conduct a minimum radiator temperature / capability test. TEST CONFIGURATION Figures 3 and 4 illustrate the TN chamber setup. Figures 5 and 6 show the Flight Thermistor, Heater and FET Layout for the OBCP and VCHP Assembly, respectively. Appendix A provides photographs. Table 3 identifies the 13 Flight Thermistors. As noted below, the test configuration included: flight hardware, test simulator the set-point temperature. The power is then regulated A test simulator of the WFC3 external radiator. to the reservoir radiator heaters, which control the Thermal Vacuum Chamber #237 at Goddard Space reservoir non-condensable gas (Nitrogen) temperature. Flight Center. This chamber had a standard feed The temperature of the gas determines the gas volume thru for the thermocouples and heater wires. in the condenser and the condenser length available for Power Supplies and a Proportional Heater Controller the VCHP ammonia working fluid. Controlling the delivered current limited power to the flight heaters effective condenser length regulates the ammonia- on the cold plate and reservoir radiator. A current saturated temperature and the amount of heat rejected sensor around the power leads determined the at the system radiator current supplied to the board. The Thermal Vacuum Data Acquisition System conditioned the signals from the test thermocouples. Thermistor Location Mnemonic Temperature Control Units (TCU's) regulated the # chamber cryopanel temperatures, which provided Thermistor (07) - VCHP boundary temperatures for the two radiators. Two Condenser Saddle ICPCONDT-A - separate cryopanels were used because the two Thermistor (07) VCHP radiators had different thermal control coatings and ICPCONDT-B required different equivalent sink temperatures. Thermistor (03) - VCHP Multi-layer Insulation provided the necessary thermal Reservoir Radiator IVC HP RT-A isolation. Thermistor (03) - VCHP 4 Reservoir Radiator IVCHPRT-B - PROPORTIONAL CONTROL Thermistor (09) VCHP 5 Evaporator IREST1 The VCHP temperature control of -5°C f 2°C is achieved Thermistor (09) - VCHP through the use of a proportionally controlled heater 7 Evaporator IREST2 zone. This system utilizes a ground programmable 9 Thermistor (07)- Cold Plate IC PLATET-A electronic thermostat to provide regulated power to the 10 Thermistor (07) - Cold Plate IC PLATET-B reservoir radiator heaters. 11 Thermistor (09) - Cold Plate ICPCTRTl The software control algorithm is a proportional function 13 Thermistor (09) - Cold Plate ICPCTRT2 that compares signals from the control temperature sensors located remotely on the VCHP evaporator with Figure 5. Cold Plate Flight Thermistor, Heater and FET Layout 13E 5501 I I / h L r r ( 32 li 19 '500 Theirnilfor 101) "ICVLATIT-A' SCAL[ I 000 Thern8,ior loll "ICPLAT[I E" trrni11.1 1091 'ICPCTRTI A' lh~rmi$lor1 091 'ICPCTRTI B' II 500 / b Thrimiitar 1091 'ICPCTRl2-A' lhermi itor 091 "ICPCTRT2-0' r 210 ~~~ Figure 6. VCHP Flight Thermistor, Heater and FET Layout VCHP FET Heater F 2x 3.73 "IVCHPRT-A" Thermistor (03). "IVCHPRT-E" VIEW B-B For each heater zone, there are two redundant control COLD CYCLING RESULTS circuits, one operating from power supplied by Low Voltage Power Supply (LVPS) 1, and one operating from BACKGROUND / PURPOSE power supplied by LVPS 2. Two control thermistors in each zone measure the zone temperature and are wired The Cold Cycling Case was run to demonstrate the so that they are averaged in the control circuitry. Both the control authority of the system when subjected to a controllers and the thermistors are redundant. simulated cold worst-case orbit-varying sink i.e., time varying sink, with a minimum cold plate heat load of five Proportional heater controllers can dissipate a significant watts. The system success criteria was to maintain the amount of power-up to 25% of the total power available OBCP average temperature at -5°C k2"C. to the zone. Therefore, the main power dissipater in the controller, the FET, is located near the heater so that the To simulate the cold on-orbit environment, transient dissipated heat is not wasted. equivalent sink temperatures were generated from the spacecraft environmental flux studies. These were then The OBCP also utilizes the same type of proportionally adjusted to account for the test configuration effects. For controlled heater zone. This zone, however, is not used the cold case, the temperature goal was to reach for stability control. During the test, it served to provide a approximately -20°C to -160°C over a 90-minute period. heat load on the cold plate for various test cases. In Two separate cryopanels were necessary due to the flight, one function of this zone is to raise the different thermal control coatings on the two radiators. temperature of the optical bench to protect it during contamination sensitive periods. To achieve the minimum sink temperatures, the TCU's provided chilled gaseous Nitrogen. For the maximum sink temperature levels, cryopanel temperature control . I ' was achieved via heated gaseous Nitrogen and test these cycles, the reservoir radiator heater power ranged heaters located on the back of the panels. from two to six watts. The available power was 1OW. The average cold plate temperature was controlled to a SUMMARY OF RESULTS nearly constant level of -5.7"C, which was within the required -5°C f 2°C temperature range. For the cold cycling test, the OBCP heater was operated in flux mode and set to the design load of five watts. The As Table 4 indicates, the system more than adequately reservoir radiator cryopanel and radiator simulator demonstrated control authority. The orbit average cryopanel were initially set to -155°C and -165OC, Reservoir Heater power was 4.5 W. This represents a respectively. The entire cycling process lasted from margin of 55% when compared to the maximum 5/29/02 15:35, to 5/30/02 0500. The goal was to get available power of 1O W. three repeatable 90-minute cycles. Table 4: VCHP Cold On-Orbit Cycling Results Summary The initial cycles reflected efforts to understand the dynamics of the cryopanels and system. The focus was Item Result to determine the appropriate TCU set points, necessary OB CP average for cold cycle -5.7 "C cryopanel heater values, and the timing of TCU set-point OB CP Control Band for cold cycle kO.1 "C changes. Challenges included the discovery that the reservoir radiator cryopanel heaters were not functional, w Orb Avg Reservoir Heater Power 4.5 and that the two TCU's shared the same LN2 line as a (10 watts maximum) cold sink resulting in them robbing LN2 from each other. The three repeatable cycles started at 5/29/02 23:49. -23 "C Figure 7 and Table 4 show key results. In Figure 7, the -143 "C left hand axis shows temperature and the right hand scale is heater power. As shown, the cryopanel equivalent sink radiators successfully cycled from -23°C to -143°C in a reDeatable 90-minute Deriod. Durina FIGURE 7. VCHP-Cold On-Orbit Cycling Case ..., -10 { ..... .. . ... .. ...... ..... . .. . .. ... .. .. . ... .. . ....... . .: ....... ... .... .. . .. .. . .. . ~ .. ;~~~ ..-~~.~ ..~. ~~~ ~~ ~ ~~ ..... .. .:.. . .... .. . . .. . . .. . . . .. . . . .~.~ .T +-R es Rad CryoPnl +R ad Sim CryoPnl +A vg Cold Plate -+ Avg Cond Saddle +A vg Rad Sim Res Rad -I- OB CP Htr Pwr +Res Rad Htr Pwr 0 . HOT CYCLING RESULTS cryopanel were set to -155°C and -165OC, respectively. The entire cycling process lasted from 6/3/02 15:37, to BACKGROUND / PURPOSE 6/4/02 05:29. The goal was to get three repeatable 90- minute cycles. The Hot Cycling Case was run to demonstrate the control authority of the system when subjected to a The initial cycles reflected efforts to cool the OBCP down simulated hot worst-case orbit-varying sink i.e., time from the +20°C level used in the previous case and to varying sink, with a maximum cold plate heat load of 15 allow the test team to exercise the cryopanels and watts. The system success criteria was to maintain the system. The focus was to determine the appropriate OBCP average temperature at -5°C +2"C. TCU set points, necessary cryopanel heater values, and the timing of TCU set-point changes. Also, during this To simulate the hot on-orbit environment, transient period, the VCHP commandable set point was lowered equivalent sink temperatures were generated from the from -5°C to -7°C. spacecraft environmental flux studies. These were then adjusted to account for the test configuration effects. For The three repeatable cycles started at 6/3/02 22:Ol and the hot case, the temperature goal was to reach concluded at 6/4/02 03:Ol. Figure 8 and Table 5 show approximately 0°C to -160°C over a 90-minute period. key temperature results. As shown, the cryopanel Two separate cryopanels were necessary due to the equivalent sink temperatures successfully cycled from different thermal control coatings on the two radiators. +1.6"C to -143°C in a repeatable 90-minute period. (In Figure 8, the plot has a lower limit of -25°C. This was To achieve the minimum sink temperatures, the TCU's done to allow for better scaling of the other temperature provided chilled gaseous Nitrogen. For the maximum results). During these three cycles, the reservoir radiator sink temperature levels, cryopanel temperature control heater power ranged from 0.0 watts to 8.4 watts. As was achieved via heated gaseous Nitrogen and test shown, there were brief periods during the orbit peak heaters located on the back of the panels. temperatures when the reservoir radiator heater went to 0.0 watts and the cold plate temperature began to rise. SUMMARY OF RESULTS During these temperature rises, the OBCP was not under active control. Since the OBCP temperature was For the hot cycling test the OBCP heater was operated in still within the requirements of -5°C k2"C, this was not flux mode and set to the design load of 15 watts. The considered a problem. VCHP commandable set point was set to -5°C and the reservoir radiator cryopanel and radiator simulator FIGURE 8. VCHP Hot On-Orbit Cycling Results i Avg ColiP late T*mp'= -5.2 C. +1.4 C. 4.7 C Constant 15 Wheat I don OBCP 1- /IoWnhoot due to Reaetvoir Radiator Environment,R es Htr OFF 9 2200 2230 23:00 233 0:00 030 1:00 l:N 2.00 2% 3:00 Time, Hours --c Res Rad Clyo -+Rad Sim Cry0 +VCHP Evap Avg X Avg Cold Plate f Avg Cond Saddle +Avg Rad Sim Res Radiator -+Res Rad Htr Pwr I . , I . . It should be noted, however, that the phenomenon of not 2. Work Order Authorization (WOA) #I0 370 “Fabricate being under active heater control was expected. The Test WFC3 VCHP TV Test MLI Blankets”, April 2, flight instrument thermal math model (TMM) predicted 2002. zero VCHP radiator heater power during the flight hot 3. “HST Wide Field Camera 3 (WFC3) Variable case peak temperatures and the test confirmed this. Conductance Heat Pipe (VCHP) Performance The SINDA TMM used a newly developed VCHP Thermal Vacuum Test Plan/Procedure ”, Document subroutine and the test results and flight predictions No. P-442-3022, Rev. A, dated June 2002 by P. looked comparable. The post-test effort will include a Cleveland. SINDA model correlation with the steady-state cases. CONTACT The orbit average Reservoir Heater power was 1.3 W. This represented a margin of 87% when compared to the Paul E. Cleveland, M.S.M.E., M.S.E., P.E. 1OW available power. As Table 5 indicates, the system Energy Solutions International, L.L.C. maintained the OBCP average temperature within the - 8705 Cathedral Way 5°C k2”C requirement. Gaithersburg, MD 20879-17 91 Tel: 240-631-6660 Table 5: VCHP Hot On-Orbit Cycling Results Summary Fax: 240-631- 6998 [email protected] It em I Result OB CP averaae for hot cvcle I -57oc I OB CP Control Band for hot cycle +1.4OC, -0.7OC ACRONYMS I Orb Avg Reservoir Heater Power (10 1.3 W watts maximum) AT Aliveness Test Reservoir Heater Power Max & Min 8.4 W, 0.0 W CCHP Constant Conductance Heat Pipe Rad Sim C/P max temp +1.6OC CP Cold Plate Rad Sim C/P min temD -1 43°C EVA Extra Vehicular Activity Res Rad Sim C/P max temp 0.6”C GEVS GSFC Environmental Verification Specification Res Rad Sim C/P min temp -1 44°C GSE Ground Support Equipment II GSFC Goddard Space Flight Center Cold plate heat load 15.0 W HST Hubble Space Telescope LN2 Liquid Nitrogen LVPS Lower Voltage Power Supply CONCLUSION MLI Multi-Layer Insulation NASA National Aeronautics and Space Administration OBA Optical Bench Assembly The objective of Cases 5 and 10 was to demonstrate the OBCP Optical Bench Cold Plate control authority of the system when subjected to a SI Science Instrument simulated cold (or hot) worst-case orbit-varying sink i.e., SM Servicing Missions time varying sink, with a minimum (or maximum) cold SM-4 Servicing Mission 4 plate heat load. The system success criteria was to maintain the optical bench cold plate at -5°C +2”C. SS Steady State TIC Thermocouple TCM Temperature Control Mode As outlined in Tables 4 and 5, these objectives have TCR Temperature Change Request been fully satisfied. TCU Temperature Control Unit T/M Thermistor ACKNOWLEDGMENTS TMM Thermal Math Model TMS Telemetry Monitoring System The authors would like to thank the NASA Goddard TN Thermal Vacuum Space Flight Center, the Hubble Space Telescope VCHP Variable Conductance Heat Pipe Project, and the Wide Field Camera 3 Project for WFC3 Wide Field Camera - 3rd generation providing the funding to carry out this work. WFPCllWide Field Planetary Camera II WOA Work Order Authorization Swales Aerospace, Inc. built the Variable Conductance Heat Pipe Assembly as well as the Optical Bench Cold Plate. REFERENCES 1. Work Order Authorization (WOA) #10564, “VCHP Thermal Vacuum Test Preparation and performance”, May 17, 2002. . I I ’ a . APPENDIX ’ Figure A-I . Full Setup & Cold Plate Top Side Figure A-3. Radiator Simulator with MLI Closeouts Figure A-4 Test Assembly with MLI Figure A-2. Radiator Simulator Instrumentation