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) 4K Cooler
Warren Holmes (JPL) Sub-K
EPIC-ized Planck Cooling Chain
EPIC
Use ~15K
Pulse Tube
for EPIC
Sunshields Added to
V-Groove Radiators
143
45
545
857
353
217
545
100
4.4K Joule-Thompson
70
ADR Baselined
30
45
4
5
(maybe 4.4K + 1.7K Stage)
30
EPIC Configuration
EPIC
•“4K” Telescope Design Includes 4th Shield
•“30K” Telescope Design Omits 4th Shield
4th shield
Launch
Configuration
Deployed Configuration
Solar Illumination and the
Scan Pattern
April 24, 2009
3
Mechanical Design
(4K Telescope Focal Plane Shown)
EPIC
Tiled Blocking Filters on Each Shield
4K Telescope = 11094 Detectors
30K Telescope = 2022 Detectors
4K 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
Black Paint
Aluminized Kapton
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
3
10
Gold, high disordered state
Al 6061-T6
Brass
2
Thermal conductivity k (w/m-K)
10
Manganin
1
10
Red - g-alumina
Blue – Effective k of strut
0
10
Teflon
-1
HTS wire
10
-2
10
0
50
100
150
200
250
T (K)
keff
k A L 
 i i i
Ag Lg 
i
300
350
Effective k
strut and wires
strut
6
Modelling Technique
EPIC
•
•
•
•
Thermal Desktop – uses finite difference method to solve a 2D 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 3D view
Model summary of temperatures, thermal resistances, radiative and conductive heat transfer.
T(K)
1st Shield
2nd Shield
3rd Shield
4th 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
4th Shield
3rd Shield
1st Shield
2nd Shield
Spacecraft
9
Spin SC at 0.5 rpm, Time Dependent Analysis
EPIC
1st Shield DT = 1.2 K pp
• Thermal isolation 4000 per
stage.
• Implies 19 pico K variation
at 4th shield.
3rd Shield DT not observable
at 3 mK level
2nd Shield DT = 0.3 mK pp
Digitization noise
10
Moonshine
EPIC
Moon
•
Moon Shine Energy Flux

qMoon  S cos  AMoon d 2
d
L2
Earth
S = Solar constant = 1350 W/m2
Amoon= p rMoon2 = disk area of the Moon = 9.49x106 km2
d = distance between L2 and the Moon = 1.54x10 6 km
 75.8 degree
90% of qMoon is infra red, 10% is visible light.
qMoon  1.33 mW/m
•
•
2
Lunar Orbit
Scaled Position of Earth, Moon and L2.
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.
0.5
a
(

)

e
(

)


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
qhot  Thot
 
qcold  Tcold
•
•



0 .5
 1 .4
Dq
or
 40% 
q
DT 1  Dq 
    10%
T
4 q 
q  e oT 4
The actual temperature should be 10% higher.
The error is about the size of uncertainties in material properties.
12
EPIC 4.4K 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 InfraRed Instrument (MIRI) on the
James Webb Space Telescope (JWST) to the EPIC requirements
Flight
Key
Cooler Control
Electronics (CCE)
Cooler Compressor Assembly
(CCA)
1553
RSA
CCE
Primary
Primary
HEC
Reed
Comp.
Valve
2X for
EPIC
Assy.
MIRI
qual ’ ed
EPIC
changes
engineering
Cooler Tower
Assembly
(CTA)
JT Compressor
J-T
J -T
CCE
Cold Head Assembly
(CHA)
De - Contamination
Field Joint
Valve
1553
J -T
Spacecraft
CCE
Red.
OMS
RSA
RSA
1553
PT
CCE
Primary
R4
R3
R2
RLDA
CCE
Red.
R1
HX
JT
HCC
Bypass
Comp.
(PT)
Precooler
Precooler
Coldhead
Coldhead
PT
1553
•
EPIC
<18K
Precooler
Precooler Environmental
Environmental
Shield
Bypass
EPIC
4.4K
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
Project
Flight
Cooler
Cooler
Electronics
Electronics
CX (2)
CX
(2)
Mini-Pulse
Mini-Pulse
AirsClass
Class (2)
Airs
(2)
HTSSE (1)
(1)
HTSSE
Stirling
Stirling
Custom
Custom
MTI (1)
MTI
(1)
Class
AirsAirs
Class
Airs Class
Class
Airs
HYPERION (1)
HYPERION
(1)
Mini-Pulse
Mini-Pulse
Hyperion Class
Class
Hyperion
SABER (1)
SABER
(1)
Mini-Pulse
Mini-Pulse
Demo
Demo
STSS (4)
STSS
(4)
Mini-Pulse
Mini-Pulse
AirsClass
Class (4)
Airs
(4)
AIRS
(2)
AIRS (2)
Class
AirsAirs
Class
AirsClass
Class (2)
Airs
(2)
TES (2)
TES
(2)
Class
AirsAirs
Class
AirsClass
Class (2)
Airs
(2)
OCO (1)
(1)
OCO
Class
AirsAirs
Class
AirsClass
Class (1)
Airs
(1)
GOSAT(1)
GOSAT(1)
HEC
HEC
HyperionClass
Class (1)
Hyperion
(1)
JAMI (2)
JAMI
(2)
HEC
HEC
HyperionClass
Class (2)
Hyperion
(2)
OPAL(2)
(2)
HTP
HEC
HEC
ACE
(8)
ACE (2)
HEC
HEC
ACE (8)
ACE
(2)
HCC/HEC-JT
10K ACE (2)
(X) Number of Flight Units
'99
'99
'00
'00
'01
'01
02
02
'03
'03
'04
'04
'05
'05
'06
'06
'07
'07
'08
'08
'09
ARGOS host
satellite
failed reached EOL
ARGOS
host
satellite
Hyperion
Class (4)
ACE
(2)
Hybrid
2 Stage
HEC
GOES
ABI
(8) (2) HEC
GOES (2)
ABI (8)
NEWT
MIRI (1)
'98
'98
In Orbit
14
4.4K 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
(mW)
Temperature
(K)
Heat Load (mW)
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 4.4K using
MIRI EM Cooler
EPIC
•
Demonstrated performance at 4.4K and anchored model used to predict the EPIC
cases for “4K” and 30K optics cases
Heat Lift at 4.4K (mW)
60
EPIC
Margined Load
4.4K Optics
50
40
EPIC
Margined Load
30K Optics
30
Measurement
anchored model
20
367 W measured input
power to compressors
10
0
0
50
100
150
200
250
300
350
Test Facility
Heat Lift at 15K (mW)
16
4.4K Cooler Bus Power Estimates
for Different Operating Points
EPIC
Parametric combinations of 4.4K and 15K loads versus bus power various loads for
the optical bench/cavity (15K) and ADR/sensor assembly (4.4K)
0.070
0.060
0.050
Lift at 4.4K (W)
•
0.040
0.030
0.020
0 mW intercept load, Model
100 mW intercept load, Model
200 mW intercept load, Model
0.010
300 mW intercept load, Model
Reference point
0.000
100
200
300
400
500
Bus Power (W)
17
Sub-K Cooler Method of Analysis
EPIC
•
•
•
•
•
Define Structure and Focal Plane Mass
– 4.4K 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 + 4.4K Cryocooler
– Planck Like Closed Cycle Dilution + 1.7K + 4.4K Cryocooler
– Parallel 3He + ADR + 1.7K + 4.4K Cryocooler Stage
Gas Gap heat Switches >1K, Superconducting Heat Switches <1K
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 1200mK and
100mK Stages
•1200mK Is Heat Intercept
Stage
•100mK Is Detector Stage
•~30% Swing in Total Power to
Cryocooler
•4 Heat Switches
Continuous Magnet Cycling
EPIC
5.0
10
Duty Cycle ~60%
Balances Power
Cryocooler
Load to 1.7K
Cryocooler
Power to 1.7K
(mW)
4.0
3.5
Intercept A
Magnet
9
Serial Continuous ADR
Black Curves Only
8
7
Intercept B
Magnet
3.0
6
2.5
5
2.0
4
1.5
3
Cryocooler
Power to 1.7K
1.0
2
0.5
1
0.0
0
0
5
10
15
Time (hours)
20
25
Magnet Current (A)
4.5
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
0
0
Load at Heat Sink (arb units)
ADR Cycle Period (arb units)
Example Intercept Tuning
Ti for Maximum
Recycle Time
Intercept Temperature (arb units)
0
Tsink
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=rljAs=Pdr ld2/(k0f Td2)
– Pd and Td Fixed by Detector Requirements and Instrument Design
– For a Metallic Heat Strap Pd / Td2 = Constant
–With No Intercept Stage Heat Straps >7kg
Lightweighting of Isothermal Detector Holders a Special Job for EPIC
–Ground Based Strategy Is “Just Add More Copper”
–In Plane Thermal Spreaders Are ~10kg 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 4K and 30KTelescope Options Differ by <2kg
•Baseline Mass Set By Cycle Time of 1Hour ~2X Gas Gap Heat Switch Cycle Time
4K Telescope Cooler System Mass Estimate
CBE Mass (kg)
20
30K Telescope Sub K Cooler System Mass Estimate
25
dashed lines - optimized for minimum reject power
power
solid lines - optimized for maximum hold time
red - parallel cycling
blue - serial cycling
20
CBE Mass (kg)
25
15
10
5
dashed lines - optimized for minimum reject power
power
solid lines - optimized for maximum hold time
red - parallel cycling
blue - serial cycling
15
10
5
0
0
0
1
2
3
Hold Time (hr)
4
5
6
0
1
2
3
Hold Time (hr)
4
5
6
Heat Load Table
EPIC
•Serial Cycled CADR Used for Mass Estimate
Units
4K Telescope
30K Telescope
Detector System Power
mW
1.76
0.34
IR Loading (Detector/Intercept)
mW
2.8/3.0
2.2/6.4
Detector Stage Heat Lift
mW
8.1
5.0
K
1.03
0.996
Intercept Stage Heat Lift
mW
205
142
Heat Strap Mass
kg
1.1
0.71
ADR System Mass
kg
7.2
6.0
mW
5.5
4.3
Intercept Temperature
ADR Cooler Load at 4.4K
Planck Dilution Principle of Operation
EPIC
10-20bar Input
0.097K
n3
n4
~ 0bar Output
JT Expansion Provides
More Additional Cooling
Planck JT at <1.4K
~200-300mircoW + Parasitics
-Undiluted 3He flow
Provides Additional Cooling of
Parasitic Loads Upto
Tricritical Point ~860mK
P~10-15microW As Pure 3He
DropletsDissolve in 4He Rich Phase
-4He flow Sets Cooling at 100mK
-P = 33 n4 f(T) T2 (mW/(mmol/sec))
-f~6.8% Saturation of 3He in 4He
-Prefactor 34 In Ideal Dilution Is 82
Lab Demo Closed Cycle Planck Dilution
EPIC
<1bar Input
0.3-0.35K
0.097K
n3
n4
-T < Superfluid Transition
-Magic 4He Purifier
-Dominant Power Source
-Pump in S/C Bus
-<100Torr
Compressed to
>800 Torr
-JT Expansion
Moved to 3He
“Input” Line
-Lift ~5microW at 100mK in Prototype
Test
-39mK Prototype Base Temperature
Continuous Cooling (3He + ADR Parallel Only)
EPIC
300mK
3He
3He
300mK
3He
3He
•Replace “High Temperature ADR
with Herschel-Like 3He Sorption
Cooler
•Feasible if Cryocooler Stage at 1.7K
•Used Cycling Powers from L.
Duband, et al Cryogenics (2006)
•Near Constant Power to Cryocooler
•8 Heat Switches
•20mW Lift Needed at 1.7K
•~ Mass of ADR/ ADR System
•Removes “High Field” ADRs
•Single Shot Option?
Sub-K Cooler - Conclusions
EPIC



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
3He + ADR
Cryocooler Temeprature
(K)
4.4 or 1.7
1.7
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
mW
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 0.5rpm 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 4.4K on ‘Flight Like Cooler’
– 4.4K Cooler Based on Current MIRI Cooler (for James Webb Space Telescope)
4K
30K
100mK Lift (mW)
ADR/ADR
0.008
0.005
4.4K Lift (mW)
Joule-Thompson
20
11
~15K Lift (mW)
Pulse Tube
68
~0
Spacecraft Power (mW)
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
0.14
0.75
0.056 *
95%
95%
Thermal
Conductivity
(W/m-K)
NA
NA
0.94
NA
0.9
Effective = 0.05
100%
NA
NA
1.2x10-6
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 @ 4.4K
Heat Reject Temperature
Bus Power at steady state
Peak cool down power
Capabilities
4.4K Optics
Capabilities
30K Optics
(Kg)
49.2
30.2
79.4
(Kg)
49.2
17.8
67.0
42mW
3000K
270W
TBD W
22mW
3000K
165W
TBD W
Operating Temperature Range (PT and JT coolers)
-20 to 50oC
Non-operating Temperature Range (PT and JT coolers)
-40 to 70oC
Operating Temperature Range (CCE)
-20 to 60oC
Non-operating Temperature Range (CCE)
-35 to 75oC
Launch Vibration (PT and JT coolers)
14.2 Grms, 1 min
Launch Vibration (CCE)
14.2 Grms, 1 min
Launch Vibration JT cooler 18K to 4.4K component
25.8 Grms, 1 min
Bus Voltage Range
Ripple Current
Communication Protocol
Lifetime
21V to 42V
100 dB micro amps
RS422/1553B
>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
0.14
0.75
0.056 *
95%
95%
Thermal
Conductivity
(W/m-K)
NA
NA
0.94
NA
0.9
Effective = 0.05
100%
NA
NA
1.2x10-6
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
4K - TDM
30K - TDM
Detector Stage Loads (in mW)
Telescope IR
2.8
2.2
Thermal IR
0
0
Heat Switch
2.1
1.8
Struts
0.91
0.56
Wires
0.43
0.1
Intercept Stage Loads (in mW)
Optimum Temperature
1.03
0.996
Telescope IR
3
6.4
Thermal IR
72
35
Heat Switch
57
58
Struts
60
41
Wires
16
4
Heat Load Table
EPIC
•Cryogenic Mass ~ 5kg Less Than ADR System
•Required Heat Lift Not Far from Prototype Demo
•No Heat Switches – 100mK Lift Is Lower
•No Magnets or Magnet Leads
•Requires Warm Pump (Like SPICA and MIRI JT Cooling Stages
Units
4K Telescope
30K Telescope
Planck
Intercept Temperature
mK
145
180
~300
Detector Stage Dissipation
mW
4.6
2.5
dn3/dt
mmole/s
15
9.7
<0.1
(temp reg)
6.7
dn4/dt
mmole/s
197
110
20
mW
4.7
2.6
-0.2
ℓ(STP)
10550
6870
4730
Cooling at 1.7 K
3He
per year if open cycle
Generic ADR Cooler Sizing
EPIC
•
•
•
•
•
Compute Heat Loads Fixed as Driven by Science Goals
Gas Gap Heat Switch for Intercept Stage
– Off State from SS Canister
– On State <50mW/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 ~T3
• Mueller Used Al – Which Won’t Work for T>~200mK
• 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 ~2.2Tesla at 6.5Amps (“Easy” to Achieve B/I Ratio)
Flux Return Shield with Soft Ferromagnetic Material