EPIC Cooling The EPIC Telescope and Focal Plane

EPIC Cooling The EPIC Telescope and Focal Plane Path to CMB Pol Workshop University of Chicago July 3, 2009 Jamie Bock (JPL) Study leader Talso Chui (JPL) Spacecraft Jeff Raab (NGAS) 4 K Cooler Warren Holmes (JPL) Sub-K

EPIC-ized Planck Cooling Chain EPIC Use ~15 K Pulse Tube for EPIC Sunshields Added to V-Groove Radiators 143 45 545 857 353 217 545 100 ADR Baselined 4. 4 K Joule-Thompson 70 30 45 4 5 (maybe 4. 4 K + 1. 7 K Stage) 30

EPIC Configuration EPIC • “ 4 K” Telescope Design Includes 4 th Shield • “ 30 K” Telescope Design Omits 4 th Shield 4 th shield Launch Configuration Deployed Configuration Solar Illumination and the Scan Pattern April 24, 2009 3

Mechanical Design (4 K Telescope Focal Plane Shown) EPIC Tiled Blocking Filters on Each Shield 4 K Telescope = 11094 Detectors 30 K Telescope = 2022 Detectors 4 K Shield (reddish) Intercept Shield (orange) Detector Stage (orange) Herschel-SPIRE Focal Plane Planck

Radiator Thermal Model EPIC Fourth Shield First Shield Aluminized Kapton Black Paint Aluminized Kapton SC Silver Teflon Acrylic overcoat Aluminum Kapton Aluminum Acrylic overcoat (b) Doubled Aluminized Kapton film (red) (a) Acrylic overcoat Aluminum Kapton Adhesive Silver with Inconel protective coat Teflon Indium Tin Oxide for charge control (c) Silver Teflon film (green) 5

Conductor Properties EPIC Gold, high disordered state Al 6061 -T 6 Brass Manganin Red - g-alumina Blue – Effective k of strut Teflon HTS wire Effective k strut and wires strut 6

Modelling Technique EPIC • • Thermal Desktop – uses finite difference method to solve a 2 D thermal equivalent electrical network. Uses RADCAD module of Thermal Desktop for Monte Carlo Ray Trace analysis. – 50, 000 rays per node. 2, 900 nodes in model. Takes ~ 8 minutes to run on a 3. 59 GHz Pentium CPU on Windows XP operating system. 7

Model Output – steady state, no active cooling, four-shields option EPIC Telescope System 3 D view Model summary of temperatures, thermal resistances, radiative and conductive heat transfer. T(K) 1 st Shield 2 nd Shield 3 rd Shield 4 th Shield Optical Box Telescope 231 116. 5 60. 39 37. 75 29. 15 22. 12 Radiative Heat Transfer to Next Stage (W) 69. 5 5. 89 0. 685 0. 0299 0. 00282 NA Conductive Heat Transfer to Next Stage (W) 3. 91 1. 07 0. 264 0. 0266 0. 01213 NA Radiative Heat Transfer to Space (W) 16, 300 75. 44 6. 00 0. 892 0. 0294 0. 0232 Thermal Resistance to next stage (K/W) 29. 3 52. 4 85. 8 323 580 NA 8

Model Output – steady state-four-shields option EPIC Optical Box 4 th Shield 3 rd Shield 2 nd Shield 1 st Shield Spacecraft 9

Spin SC at 0. 5 rpm, Time Dependent Analysis EPIC 1 st Shield DT = 1. 2 K pp • Thermal isolation 4000 per stage. • Implies 19 pico K variation at 4 th shield. 3 rd Shield DT not observable at 3 m. K level 2 nd Shield DT = 0. 3 m. K pp Digitization noise 10

Moonshine EPIC Moon • Moon Shine Energy Flux q d L 2 Earth S = Solar constant = 1350 W/m 2 Amoon= p r. Moon 2 = disk area of the Moon = 9. 49 x 106 km 2 d = distance between L 2 and the Moon = 1. 54 x 106 km q= 75. 8 degree 90% of q. Moon is infra red, 10% is visible light. Lunar Orbit Scaled Position of Earth, Moon and L 2. Dimensions are in units of 106 km. At Apogee Moon shine touches redpurple area • • At Apogee - Small Amount of Moon Shine Illuminates Back of Telescope Heating From Moon Is Negligible 11

“Greying” of Radiative Coatings EPIC • • • Software Tool Assumption – Absorptivity/Emissivity Is Independent of Wavelength. Metal Coated Surfaces Colder Surface Emissivity (e) Always Less Than Absorptivity (a) Software Tool Under Estimates Heat Transfer from Hot to Cold Side in V -Grooves The actual temperature should be 10% higher. The error is about the size of uncertainties in material properties. 12

EPIC 4. 4 K Cooler – Extension of MIRI Cooler Design EPIC The approach to the Experimental Probe of Inflationary Cosmology (EPIC) cryocooler is to define low-risk hardware and software with minimal changes from flight heritage designs. This approach minimizes cost, schedule, and risk by adapting the very similar design developed for the Mid Infra. Red Instrument (MIRI) on the James Webb Space Telescope (JWST) to the EPIC requirements Flight Key Cooler Control Electronics (CCE) Cooler Compressor Assembly (CCA) 1553 J-T J -T CCE RSA CCE Primary HEC Reed Comp. Valve 2 X for EPIC Assy. MIRI qual ’ ed EPIC changes engineering Cooler Tower Assembly (CTA) JT Compressor Cold Head Assembly (CHA) De - Contamination Field Joint Valve 1553 J -T Spacecraft CCE Red. RSA 1553 PT CCE Primary R 4 R 3 R 2 CCE Red. HX JT HCC Bypass Comp. (PT) OMS R 1 RLDA Precooler Coldhead PT 1553 • EPIC <18 K Precooler Environmental Shield Bypass EPIC 4. 4 K PT – Pulse tube JT – Joule Thompson CCE – Cryocooler Control Electronics HEC – High eff. compressor HCC – High capacity compressor RX – Recuperators 13

Cryocooler Flight History and Reliability EPIC NGAS Flight Coolers Are Reliable- All performing nominally Flight Project Flight Cooler Electronics CX (2) Mini-Pulse Airs. Class (2) Airs (2) HTSSE (1) HTSSE Stirling Custom MTI (1) Class Airs Class Airs HYPERION (1) Mini-Pulse Hyperion Class Hyperion SABER (1) Mini-Pulse Demo STSS (4) Mini-Pulse Airs. Class (4) Airs (4) AIRS (2) Class Airs. Class (2) Airs (2) TES (2) Class Airs. Class (2) Airs (2) OCO (1) OCO Class Airs. Class (1) Airs (1) GOSAT(1) HEC Hyperion. Class (1) Hyperion (1) JAMI (2) HEC Hyperion. Class (2) Hyperion (2) OPAL(2) HTP HEC HEC ACE (8) ACE (2) HCC/HEC-JT 10 K ACE (2) (X) Number of Flight Units '99 '00 '01 02 02 '03 '04 '05 '06 '07 '08 '09 ARGOS host satellite failed reached EOL ARGOS satellite Hyperion Class (4) ACE (2) Hybrid 2 Stage HEC GOES ABI (8) (2) HEC GOES (2) ABI (8) NEWT MIRI (1) '98 In Orbit 14

4. 4 K Cryocooler Cooling Loads for MIRI and EPIC Applications EPIC • The EPIC requirements with 100% cooling margin are well with-in the capability of the MIRI cooler MIRI EPIC Temperature (K) Heat Load (m. W) Stage 4 6. 2 65 4. 4 42 Stage 3 17 -18 78 <18 134 Reject Temperature 313 K 300 K Bus Power (steady state) 400 W 270 W Bus Power (cooldown) 475 W TBD 15

Measured JT Cooling at 4. 4 K using MIRI EM Cooler EPIC • Demonstrated performance at 4. 4 K and anchored model used to predict the EPIC cases for “ 4 K” and 30 K optics cases EPIC Margined Load 4. 4 K Optics EPIC Margined Load 30 K Optics Test Facility 16

4. 4 K Cooler Bus Power Estimates for Different Operating Points EPIC • Parametric combinations of 4. 4 K and 15 K loads versus bus power various loads for the optical bench/cavity (15 K) and ADR/sensor assembly (4. 4 K) 17

Sub-K Cooler Method of Analysis EPIC • • • Define Structure and Focal Plane Mass – 4. 4 K Shield, Thermal Intercept Stage, Detector Stage – CAD Model + Mag Shields Scaled from SPIDER Actual Mass – Size “Magic” Ti 15 -3 -3 -3 Struts for Launch Loads Compute Direct Heat Loads – “Non Signal” Thermal IR Transmitted or Emitted by Blocking Filters – Detector and SQUID Bias Loads – Cable Heat Leak (SPIRE-Like Cables, Nb-Ti Wires) Compute Performance for Different Coolers – ADR + 4. 4 K Cryocooler – Planck Like Closed Cycle Dilution + 1. 7 K + 4. 4 K Cryocooler – Parallel 3 He + ADR + 1. 7 K + 4. 4 K Cryocooler Stage Gas Gap heat Switches >1 K, Superconducting Heat Switches <1 K Vandium Permendur Flux Return Magnet Shield

Adiabatic Demagnetization Refrigerator (ADR) EPIC – – ‘On State’ During Magnetization (AB) ‘Off State’ During Adiabatic Demag (BC) Isothermal Demagnetization (CD) Warm Up (AD) and Repeat Cycle A-B-C-D Reject Heat at High T Absorb Heat at Low T

Continuous Cooling (Serial Method Shown) EPIC • Paired ADRs Alternate Cycling to Maintain Constant Temperature at 1200 m. K and 100 m. K Stages • 1200 m. K Is Heat Intercept Stage • 100 m. K Is Detector Stage • ~30% Swing in Total Power to Cryocooler • 4 Heat Switches

Continuous Magnet Cycling EPIC Cryocooler Serial Continuous ADR Black Curves Only

Intercept Temperature Tuning EPIC • Optimum Temperature of Intercept (Ti) Depends on Parasitics So Is Unique for Configuration • Each Configuration Has Choice of Optimum Ti - Maximum Cycle Time or Lowest Cryocooler Load Ti for Minimum Cryocooler Load Ti for Maximum Recycle Time

Heat Straps and Detector Holder Thermal Engineering EPIC • • • Cooler to Focal Plane Heat Strap Design Important Regardless of Cooler Heat Strap Mass Fully Constrained – m=rlj. As=Pdr ld 2/(k 0 f Td 2) – Pd and Td Fixed by Detector Requirements and Instrument Design – For a Metallic Heat Strap Pd / Td 2 = Constant –With No Intercept Stage Heat Straps >7 kg Lightweighting of Isothermal Detector Holders a Special Job for EPIC –Ground Based Strategy Is “Just Add More Copper” –In Plane Thermal Spreaders Are ~10 kg for SCUBA II –Space Designs Need Optimization

Mass Estimates EPIC • Serial Operated ADR, Optimized for Longest Cycle Time, Is Least Massive (Baseline) • Sub K Cooler for 4 K and 30 KTelescope Options Differ by <2 kg • Baseline Mass Set By Cycle Time of 1 Hour ~2 X Gas Gap Heat Switch Cycle Time X X

Heat Load Table EPIC • Serial Cycled CADR Used for Mass Estimate Units 4 K Telescope 30 K Telescope Detector System Power m. W 1. 76 0. 34 IR Loading (Detector/Intercept) m. W 2. 8/3. 0 2. 2/6. 4 Detector Stage Heat Lift m. W 8. 1 5. 0 K 1. 03 0. 996 Intercept Stage Heat Lift m. W 205 142 Heat Strap Mass kg 1. 1 0. 71 ADR System Mass kg 7. 2 6. 0 m. W 5. 5 4. 3 Intercept Temperature ADR Cooler Load at 4. 4 K

Planck Dilution Principle of Operation EPIC 10 -20 bar Input 0. 097 K n 3 n 4 ~ 0 bar Output JT Expansion Provides More Additional Cooling Planck JT at <1. 4 K ~200 -300 mirco. W + Parasitics -Undiluted 3 He flow Provides Additional Cooling of Parasitic Loads Upto Tricritical Point ~860 m. K P~10 -15 micro. W As Pure 3 He Droplets. Dissolve in 4 He Rich Phase -4 He flow Sets Cooling at 100 m. K -P = 33 n 4 f(T) T 2 (m. W/(mmol/sec)) -f~6. 8% Saturation of 3 He in 4 He -Prefactor 34 In Ideal Dilution Is 82

Lab Demo Closed Cycle Planck Dilution EPIC <1 bar Input 0. 3 -0. 35 K 0. 097 K n 3 n 4 -T < Superfluid Transition -Magic 4 He Purifier -Dominant Power Source -Pump in S/C Bus -<100 Torr Compressed to >800 Torr -JT Expansion Moved to 3 He “Input” Line -Lift ~5 micro. W at 100 m. K in Prototype Test -39 m. K Prototype Base Temperature

Continuous Cooling (3 He + ADR Parallel Only) EPIC 300 m. K 3 He 3 He • Replace “High Temperature ADR with Herschel-Like 3 He Sorption Cooler • Feasible if Cryocooler Stage at 1. 7 K • Used Cycling Powers from L. Duband, et al Cryogenics (2006) • Near Constant Power to Cryocooler • 8 Heat Switches • 20 m. W Lift Needed at 1. 7 K • ~ Mass of ADR/ ADR System • Removes “High Field” ADRs • Single Shot Option?

Sub-K Cooler - Conclusions EPIC l l l Sized Different Coolers Technologies For EPIC ADR Mass and Power Performance Within Prototype Capabilities Closed Cycle Planck Dilution Cooler Feasible Units ADR/ADR Closed Planck Dilution 3 He + ADR Cryocooler Temeprature (K) 4. 4 or 1. 7 Cryogenic Mass kg 9. 5 or < 9. 5 ~5 <9. 5 Cryogenic Magnetic Field yes no yes Heat Switches Heat Load to Cryocooler 4 8 or ~3 0 <10 8 >20 Partial Ice Plug Heater Partial 20 150 -200 12 m. W Cryogenic Fault Tolerance Warm Electronics – Cooler Operation Only W

Summary of Results • Detailed Radiative Modelling of Spacecraft with “Systematics” Checks – – EPIC Model Accuracy ~0. 5% Non-Axial Temperature Variations Negligible (at 0. 5 rpm Spin Rate) Moon Shine Is Negligible Greying of Emissivity and Absorptivity ~10% Corrections to Model Results • Cryocooler Requirements Within Reach of Current Technology – Characterizations Performed at 4. 4 K on ‘Flight Like Cooler’ – 4. 4 K Cooler Based on Current MIRI Cooler (for James Webb Space Telescope) 4 K 30 K 100 m. K Lift (m. W) ADR/ADR 0. 008 0. 005 4. 4 K Lift (m. W) Joule-Thompson 20 11 ~15 K Lift (m. W) Pulse Tube 68 ~0 Spacecraft Power (m. W) Radiator 290000 185000 Sub-K Cooler (kg) Cryo-mass only 7. 2 6. 0 Cryocooler (kg) Cryo+pumps+readout 79. 4 67. 7 30

Planck Launch EPIC 143 45 545 857 353 217 545 100 70 30 45 30 4 5 PLANCK is now a "stellar object" of an estimated magnitude 18. 5 in the Ophiuchus constellation.

Backups EPIC 32

Optical Properties EPIC Optical properties of coating materials at 300 K Coating Solar Absorptivity Infrared Emissivity Specularity Silver Teflon Aluminized Kapton Black Paint MLI 0. 14 0. 75 0. 056 * 95% Thermal Conductivity (W/m-K) NA NA 0. 94 NA 0. 9 Effective = 0. 05 100% NA NA 1. 2 x 10 -6 0. 06 Emissivity of Aluminized Kepton versus T 0. 055 Inherited from SAFIR 0. 05 Emissivity 0. 045 0. 04 0. 035 0. 03 0. 025 0. 02 0. 015 0. 01 0 50 100 150 T (K) 200 250 300 33

EPIC Cryocooler Properties Summary EPIC Instrument Mass (Best Estimate) Cooler Assembly (JT/ PT Pre-cooler) Electronics (JT/Pre-cooler/Switch box) Total Nominal Operating Condition Cooling Load @ 4. 4 K Heat Reject Temperature Bus Power at steady state Peak cool down power Capabilities 4. 4 K Optics Capabilities 30 K Optics (Kg) 49. 2 30. 2 79. 4 (Kg) 49. 2 17. 8 67. 0 42 m. W 3000 K 270 W TBD W 22 m. W 3000 K 165 W TBD W Operating Temperature Range (PT and JT coolers) -20 to 50 o. C Non-operating Temperature Range (PT and JT coolers) -40 to 70 o. C Operating Temperature Range (CCE) -20 to 60 o. C Non-operating Temperature Range (CCE) -35 to 75 o. C Launch Vibration (PT and JT coolers) 14. 2 Grms, 1 min Launch Vibration (CCE) 14. 2 Grms, 1 min Launch Vibration JT cooler 18 K to 4. 4 K component 25. 8 Grms, 1 min Bus Voltage Range Ripple Current Communication Protocol Lifetime 21 V to 42 V 100 d. B micro amps RS 422/1553 B >10 years 34

Optical Properties EPIC Optical properties of coating materials at 300 K Coating Solar Absorptivity Infrared Emissivity Specularity Silver Teflon Aluminized Kapton Black Paint MLI 0. 14 0. 75 0. 056 * 95% Thermal Conductivity (W/m-K) NA NA 0. 94 NA 0. 9 Effective = 0. 05 100% NA NA 1. 2 x 10 -6 0. 06 Emissivity of Aluminized Kepton versus T 0. 055 Inherited from SAFIR 0. 05 Emissivity 0. 045 0. 04 0. 035 0. 03 0. 025 0. 02 0. 015 0. 01 0 50 100 150 T (K) 200 250 300 35

ADR Heat Load Breakdown EPIC • Serial Cycled CADR 4 K - TDM 30 K - TDM Detector Stage Loads (in m. W) Telescope IR 2. 8 Thermal IR 0 Heat Switch 2. 1 Struts 0. 91 Wires 0. 43 Intercept Stage Loads (in m. W) Optimum Temperature 1. 03 Telescope IR Thermal IR Heat Switch Struts Wires 3 72 57 60 16 2. 2 0 1. 8 0. 56 0. 1 0. 996 6. 4 35 58 41 4

Heat Load Table EPIC • Cryogenic Mass ~ 5 kg Less Than ADR System • Required Heat Lift Not Far from Prototype Demo • No Heat Switches – 100 m. K Lift Is Lower • No Magnets or Magnet Leads • Requires Warm Pump (Like SPICA and MIRI JT Cooling Stages Units 4 K Telescope 30 K Telescope Planck Intercept Temperature m. K 145 180 ~300 Detector Stage Dissipation m. W 4. 6 2. 5 dn 3/dt mmole/s 15 9. 7 <0. 1 (temp reg) 6. 7 dn 4/dt mmole/s 197 110 20 m. W 4. 7 2. 6 -0. 2 ℓ(STP) 10550 6870 4730 Cooling at 1. 7 K 3 He per year if open cycle

Generic ADR Cooler Sizing EPIC • • • Compute Heat Loads Fixed as Driven by Science Goals Gap Heat Switch for Intercept Stage – Off State from SS Canister – On State <50 m. W/K (JPL Design) – 60% Duty Cycle for Continuous Superconducting Heat Switches for Detector Stage – Switch Design Based on Mueller et al Rev Sci Inst (49) 515 (1978) – On State Fixed for 1% Gradient at Operating Point – Off State Phonon Conduction ~T 3 • Mueller Used Al – Which Won’t Work for T>~200 m. K • Use V or “Switching Ratio” ~500 Used in Model • Pb Switching Ratio ~100 Backup, But Would Lower Ti (Heer, et al, Rev. Sci. Inst. 25, 1088 (1954) Maximum Field ~2. 2 Tesla at 6. 5 Amps (“Easy” to Achieve B/I Ratio) Flux Return Shield with Soft Ferromagnetic Material