JWST Thermal Systems Thermal Design Challenges and Status …safir.jpl.nasa.gov/BeyondSpitzerConf/proceedings/session... · 2004-08-23 · 2 JWST Thermal Systems JWST Mission Overview

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JWST Thermal Systems

Thermal Design Challenges and Status of NASA’s James

Webb Space Telescope

Keith ParrishSunshield Manager

Thermal Systems Lead EngineerNASA Goddard Space Flight Center

Acknowledgments

Shaun Thomson (NASA)John Pohner (NGST)

From Spitzer to Herschel and Beyond: The Future of Far-Infrared Space Astrophysics ConferenceJune 7, 2004

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JWST Mission Overview

JWST Observatory Overview

JWST Thermal Architecture and Requirements

Sunshield

Integrated Science Instrument Module (ISIM)

Thermal Design Challenges

ISIM Warm Electronic AccomodationCool-Down Control/Contamination designSunshield/Bus Closeout

Verification and Modeling philosophy

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James Webb Space Telescope Cryogenic Infrared Observatory at a

Glance

• Mission Objective– Detailed study of the birth and evolution galaxies– Optimized for near infrared wavelength (0.6 –28 µm)

• Organization– Mission Lead: Goddard Space Flight Center– International collaboration with ESA & CSA – Prime Contractor: Northrop Grumman Space Technology– Instruments:

– Near Infrared Camera (NIRCam) – Univ. of Arizona– Near Infrared Spectrometer (NIRSpec) – ESA– Mid-Infrared Instrument (MIRI) – JPL/ESA– Fine Guidance Sensor (FGS) – CSA • Description

– Approx. 6 m diameter deployable, active optics, primary mirror– Launched by Ariane 5(TBR) from Kourou, French Guiana,

direct insertion to L2 orbit– Integrated Science Instrument Model (ISIM) consisting of 3

science instruments and a guider• Website

– www.JWST.nasa.gov

FY99 FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY08 FY09Formulation Phase (A/B) Implementation Phase (C/D)

SelectPrime SRR PDRNAR CDR

FY10

Launch Timeframe

FY11

MOR

4


JWST builds on achievements of SST/HST

Spitzer Space Telescope

JWST• Collecting area• Angular resolution • Low backgroundHubble Space Telescope

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JWST – Observatory Overview

Primary Mirror

Secondary MirrorSpacecraft

Sunshield

Aft Optics Subsystem

Integrated Science Instrument Module

ISIM Thermal Enclosure

Telescope Structure

Primary Mirror

Secondary MirrorSpacecraft

Sunshield

Aft Optics Subsystem

Integrated Science Instrument Module

ISIM Thermal Enclosure

Telescope Structure

GSFC,JPL,ESA,CSA,UofA

Telescope I&T

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Launch Vehicle Challenges

• Launch vehicle is Ariane 5(TBR)

• Must maintain compatibility with US EELV Heavy

• Even on these vehicles JWST is extremely mass challenged

– 6000-7000 kg

– Mirror fabrication has begun. Mass of telescope is soon non-negotiable

• Servicing of SH2 Dewar at launch site and on-vehicle at pad

• Potential solar illumination of mirrors and large radiators

~15 m

during launch phase.

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Thermal Architecture Overview

5 – Layer SunshieldAttenuates and re-directs solar energyCold side layer ~ 50 to 100 K

ISIM Enclosure Radiator, >8 m2

Cools NIR detectors and instrument optics,37 – 40 K, ~ 297 mW dissipation, harness loads

OTE primary and secondary mirrors passively cooled, 30-50 K

Central Baffle/RadiatorPassively cools aft optics to <40 K,20 mW

SH2 DewarCools MIRI detector < 7 K, 10 mW

bench < 13.5 K 50 mW

Deployment TowerMechanical/thermal isolation,Increases OTE/ISIM to space view

ISIM Warm ElectronicsDedicated radiators, isolation system290 K, FPA harness length restricted

SpacecraftOn warm side, typical thermal control,20-40 C

JWST is configured to be a passive multi-stage cryogenic radiator system

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System/Thermal Requirements Inter-Relationships

MR-211 Optical Transmission

Accounting for all effects on mirror transmission including: coatings, dust obscuration, meteoroid damage, and contamination, the End of Life (EOL) optical spectral transmission of the OTE shall be greater than the values shown in the following table for wavelengths between 0.6 µm and 2.0 µm, and greater than 88% for wavelengths from 2.0 µm to 27 µm.

System Thermal Models

•Sunshield, OTE, ISIM, Instrument steady state temperature profiles• Cool down profiles• Thermo-optical properties• Thermal model geometry

Stray-light AnalysesContamination Analyses

Sensitivity V

erificationmodeling

MR-122 Stray Light From Thermal Emissions

Thermal emissions from the Observatory that reach the final OTE focal plane shall contribute less flux than that from an equivalent on-axis astronomical source whose brightness is 3.9 MJy/sr and 200MJy/sr, at 10 µm and 20 µm respectively.

MR-51 Sensitivity

allocations

Thermal Requirements•Baffle/shielding/coatings•Optics temperatures•Cool-down and gradient control

Specification Inputs*heater control and design*sunshield attenuation performance *coatings

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System/Thermal Requirements Inter-Relationships

MR-113 Encircled Energy 24 Hour Stability

Without requiring ground-commanded correction, there shall be less than 2 percent root-mean-squared (RMS) variation about the mean encircled energy, defined to be at 0.15 arc-second radius at a wavelength of 1µm, over a 24 hour period.

MR-114 Conditions

The 24 hour stability requirements shall be met for any combination of target pointings within the field of regard (FOR), including those separated by a slew with a thermally worst-case 10 degree pitch change.

Image Quality

MR-178 Re-Pointing

Re-pointing time for any slew less than or equal to 90 degrees shall be less than 60 minutes, which includes mechanical and thermal settling, and guide star acquisition.


•OTE Temperature Stability•ISIM/Instrument Temperature Stability• Bulk Average Steady State Temps

Dimensional Stability/Optical Analyses

Image Q

uality V

erification

Thermal Requirements•Temperature Stabilities•Bulk Average Temperatures•Cool-down and gradient control

modeling

allocationsIRD/ICD Inputs Specification Inputs*Power Stability *heater control and design*Interface Stability *sunshield attenuation performance

*composite lay-up zero CTE temp

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Thermal Specific Requirements - Passive Cooling of NIR Detectors

AllocationPassive cooling is mission enabling.Passive cooling requires complete architecture solution.37 K based on HgCdTe detector performance. HgCdTe technology selected over colder 30 K InSB 37 K is a well defined hard limit. Observatory thermal architecture is driven by this requirement.This requirement flows down in some aspect to all

observatory, element, and subsystem IRDs and specifications.

Rationale

MR-270 Architecture

The observatory architecture shall allow for the passive cooling of ISIM-related components and electronics to their safe and operational limits

MR-271 NIR IR Detector Cooling

The Observatory shall passively cool the NIR Science Detectors to a temperature of 37K beginning at a time during commissioning that supports NIRCam and NIRSpec commissioning and continuing until the end of the science mission lifetime.

OBS-176 Near Infrared Detector CoolingThe Observatory shall passively cool the NIR Detectors to a temperature of 37 K beginning at a time during commissioning that supports NIRCam and NIRSpec commissioning and continuing until the end of the science mission lifetime.

SpacecraftSCE (OBS-1610) Solar Shielding

The Spacecraft shall shield the ISIM to allow for the passive cooling of the near infrared (NIR) detectors following the commissioning of the science instruments (SIs).

OTEISIM to OTE and Spacecraft IRD

JWST-IRD-000640D36129

Flow-down Example

ISIMISIM Requirement Document ISIM thermal subsystem heat transport requirements

ISIM enclosure radiator requirements

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Thermal Specific Requirements – Cryogenic Heat Rejection Capacity Margin

Allocation

MR-91

The calculated margin on the heat rejection capacity of cryogenic systems shall be no less than 50% at the Critical Design Review (CDR). (This requirement does not apply to stored cryogen.) For all cryogenic components(<100 Kelvin), margin is defined as excess heat rejection capacity as a percentage of the calculated load. Calculated load includes power dissipation and predicted radiative and conductive parasitics. Heat rejection capacity is calculated at the maximum allowable operating temperature. Excess capacity isdefined as the rejection capacity minus the calculated load

Cooling margin and temperature combine to drive overall architecture – radiator sizes, power allocation, related mass. Margin is held as reserve until design is solidified and thermal models account for all potential heat loads.Unique thermal nature of JWST requires judicious use of of objective and well-defined cryogenic design practices

Rationale

Discussion/Example100(%)margin 4

44

predicted

predictedrequired

TTT −

=


•power dissipation allocations •parasitic allocations (loads based on harness models, etc.)• worse case environment• end-of-life thermo-optical properties, minimum radiator emittances• maximum interface boundaries, temperature drops• hottest attitude

Modeling allocations

NIR detector temperature prediction

Prediction must be <32.1 K to meet 50% requirement

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Sunshield Architecture

19.5 M

11.4 M 5.3 M

2.4 M

10.3 M

0.95 M

6.74 M

19.5 M

11.4 M 5.3 M

2.4 M

10.3 M

0.95 M

6.74 M

11.4 M 5.3 M

2.4 M

10.3 M

0.95 M

6.74 M

45°

V3

5°

V1 ± 5° Rotation

± 5°

Permissible Sun Orientations

45°

V3

5°

V1 ± 5° Rotation

± 5°45°

V3

5°

V1 ± 5° Rotation

± 5°

Permissible Sun Orientations

Sunshield Containment Envelope

Fwd Boom Launch Restraint (2 pl)

5 layers of Kapton E with silicon and VDA coatings

Solar attenuation of 10-7

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What is ISIM? • The JWST Science Instruments • Associated Infrastructure: Structure, C&DH, & FSWRegion 1 (Cryogenic Region, 6K to 40 K)Science Instrument Optics Assemblies

Near Infra-Red Camera (NIRCam)Near Infra-Red Spectrometer (NIRSpec)Mid Infra- Red Instrument (MIRI), & DewarFine Guidance Sensor (FGS)FGS Tunable Filter Instrument (FGS/TF)

Radiators and support structure (NGST supplied)

Region 2 (approximately 290 K)Focal Plane Electronics (FPE)Instrument Control Electronics (ICE), MCE,DCEFine Steering Mirror (FSM) Differential Impedance Transducer (DIT)

Region 3ISIM Command & Data Handling (C&DH) ElectronicsFGS C&DH Electronics

ISIM Overview

MCE- MEMS Control Electronics, DCE Dewer Control Electronics

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JWST Thermal SystemsOverall ISIM Thermal Control Network

Basic Solution:1. Establish passive heat sinks held below

required temperatures (MIRI excepted)2. Move dissipated heat efficiently from

Instruments & Detectors to heat sinks3. Limit introduction of Parasitic Heat4. Maintain temperatures and rates of

temperature change within acceptable limits throughout test & mission

5. Control power dissipation levels of detectors & instrument mechanisms

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JWST Thermal SystemsGSFC ISIM/Observatory TMG Thermal Model

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Thermal Design Challenges – ISIM Warm Electronics•ISIM detector electronics (290 K) need to be incompatibly close (<6m) to cryogenic (region 1) area.

• Extensive trade study now underway to optimize this critical thermal design area.

• Harness design critical (>3000 wires + shielding from warm electronics to Region 1

•Harness materials and size chosen to minimize conduction/Joule heating over large temperature range

IEC, 200 W, 293 K

ISIM Electronics Compartment (IEC)

•Soft mounted to and deploys with OTE/ISIM

•Launch locked/load carried to bus

•Specular baffles/radiator ‘funnel’ heat away from cold sunshield layer

•Muliple specular shields and parasitic guard radiators separate IEC from ISIM/Telescope

OTE/ISIM, 300 mW, 30-50 K

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Thermal Design Challenges – Cool-down Control/Contamination

•Natural on-orbit cool-down is incompatible with contamination requirements and on-station steady state design

• optics and detectors naturally cool the quickest, drawing water from outgassing composite structures

• Mid-IR instrument is highly isolated to maximize cryogen lifetime. Does not want to cool-down

• On-orbit cool down period period (90-110 days) is not-practical for ground testing.

• Goal of 30 day test cool-down requires design features which are not compatible with low parasitic steady-state design.

Heat Switches and Heaters

Commandable heat switches “break” connection between components and radiators

•Enables protection of detectors from possible overheating during pre-deployment.

•MIRI heat switch (MIRI responsibility) connects instrument to dewar and keeps dewar isolated until ISIM environment and MIRI instrument temperature drops below 70K

–Minimizes cryogen losses & extends MIRI lifetime

Development underway

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Thermal Design Challenges – Sunshield/Bus Closeout

Sunshield needs effective closeout over warm busDesign on-going to mechanically accommodate

BSF

Tower

Spacecraft

BSF

Tower

Spacecraft

BSF

Tower

Spacecraft

BSF

Tower

SpacecraftSTOWED

DEPLOYED

Sunshield stowed internal to BSF

Sunshield containment

hardware

Sunshield inner support frame

Deployed sunshield extends across SC

Prior base-line has MLI only ‘hole’ across spacecraft bus

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Thermal Design Challenges – Verification and Modeling

JWST Thermal Modeling and Verification Realities

• large passive cryogenic system modeling in regime with very little flight heritage

• accurate model results are used in JWST design (mirror fabrication, optical stability, operations, instrument sensitivity, science goals and performance,etc.)

• large multi-national organization with a variety of modeling tools and practices

• difficult/ill-definable thermal interfaces

• piece-meal verification over several years, no flight configuration thermal balance

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Modeling Plan•Thermal modeling results are used extensively and uniquely to verify system level requirements and to develop and refine lowerlevel requirements.

•Thermal modeling results are used extensively and uniquely to develop interface requirements and design specifications (e.g. OTE backplane composite lay-up, MIRI dewar interfaces)

•Model validation is segmented and takes place over several years.

Modeling Plans and Quality Control•Observatory performance will be assessed via two different independent modeling methodologies.

GSFC Observatory Modeling• IDEAS/TMG (finite element modeler)• ISIM Design and Instrument Analysis• Observatory Performance

NGST Observatory Modeling• TSS/SINDAG (NASA Standard finite difference)• Observatory Design and Analysis (SC,OTE,SS)• ISIM Performance

Quarterly model results and assumption auditsPerformance metrics from both models compared and trackedCommon material and optical property databasesIndependent, but common format, high level and detailed heat maps

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Thermal Verification Road Map – Visual Example

ISIMEnclosure

Spacecraft

Sunshield

OTE

ISIM

TIE1. Radiator Coating Coupons

TIS2. Bench Material Property Tests (k vs. T)

TIS4. SI Mounting& Housing Cooling

TIC1. CS MountingMethods (H/W owner?)

TIS3. Harness Development Test (Small Sample)

TIC1. Cryo CoolerLine Parasitics

TIS9. OTE Interface H/W

Deliver

ETU ISIM

Deliver

FLT ISIM

E17 ETU ISIMTB TEST

3/08 8/08

OT14 ETU ISIM/OTE PF TEST

TBD TBD

IS8 FLIGHT ISIMTB TEST

4/09 9/09

OB7 FLIGHT ISIM /OTE TEST

12/09 4/10

IEC

ScienceInstruments

TSC1. S/C +z MLILay-up (ε*)

SC7. SC Thermal Balance Test

TSS1. Silicon KaptonEnv. Testing

TSS2. VDA SpecularityVs. Contam. Level

TSS3. MicrometeoroidTesting

SP1. SS SubscaleThermal Balance Test

TOT1. Tower T300Conductivity vs. T

Deliver SCTo Observatory

TIE2. M55J BoronConductivity vs. T

TIE3. Cryo External MLI Lay-up (ε*)

Select MIRI Cooling: CC vs. CS

Flight SSDesign & Build

Deliver SSTo Observatory

CS

CC

Final ISIMThermalDesign

Final ISIMDesign

TIE5. Pathfinder RadiatorThermal Balance Test

TIEC1. FPE TCSHardware Simulator

TIEC2. FPE Unit LevelDissipation & Stability

Should this go to

ETU ISIM/PF OTE?

ENC1/ENS1/EFG1. ETU Thermal Perf. Test• FPA isolation from housing

• dissipation & stabilityNIR

MIRI

FNC1/FNS1/FFG1. Flight SI Thermal Perf. Test• FPA isolation from housing

• dissipation & stability FMI1. Flight SI Thermal Perf. Test• FPA isolation from housing

• dissipation & stability FMC1. Flight SI & Cooling SystemThermal Performance Test• Cryocooler or Cryostat

Deliver MIRITo ObservatoryPost Test OB7?

TOT2. OTE CoatingsEmissivity TestsAt Cryo Temps

TOT3. PMSA EDUAssembly Conductances,

Actuator Dissipations

NGST

Ball

GSFC

SI Mfr

Test Responsibility

8/03

8/04 11/04

TIS6. Heat Strap / Harness Standoff Test

TIS7. Structure JointConductance Test

TIS8. Harness Test (End to End) Thru Temp Regimes

TIS5. ISIM Coating εat Cryogenic Temp

1/0510/04

TIS1. Strap Development Test

1/04 4/04

TIE4. Radiator Coating- Large Samples

4/04 7/04

TBD TBD

12/039/03

11/02 9/03

12/03 1/04

10/04 1/056/04 9/04

9/03 12/03

10/04 1/05

TBD TBD

TOT4. SMA EDUAssembly Conductances,


1/04 4/04 1/06 4/06

7/06 10/06

ISIM Thermal CDR – 1/05

ISIM Thermal PDR – 1/04

TIS10. Heat Switch& Miscellaneous

Thermal H/W 6/05 9/05

CC1 /CS1. Cooler Thermal Perf. TestCooling performance in 30K env.

TIEC3. FPE TCSFlt H/W Test

ISIMEnclosure

Spacecraft

Sunshield

OTE

ISIM

TIE1. Radiator Coating Coupons

TIS2. Bench Material Property Tests (k vs. T)

TIS4. SI Mounting& Housing Cooling

TIC1. CS MountingMethods (H/W owner?)

TIS3. Harness Development Test (Small Sample)

TIC1. Cryo CoolerLine Parasitics

TIS9. OTE Interface H/W

Deliver

ETU ISIM

Deliver

ETU ISIM

Deliver

FLT ISIM

Deliver

FLT ISIM

E17 ETU ISIMTB TEST

3/08 8/08

OT14 ETU ISIM/OTE PF TEST

TBD TBD

IS8 FLIGHT ISIMTB TEST

4/09 9/09

OB7 FLIGHT ISIM /OTE TEST

12/09 4/10

IEC

ScienceInstruments

TSC1. S/C +z MLILay-up (ε*)

SC7. SC Thermal Balance Test

TSS1. Silicon KaptonEnv. Testing

TSS2. VDA SpecularityVs. Contam. Level

TSS3. MicrometeoroidTesting

SP1. SS SubscaleThermal Balance Test

TOT1. Tower T300Conductivity vs. T

Deliver SCTo Observatory

TIE2. M55J BoronConductivity vs. T

TIE3. Cryo External MLI Lay-up (ε*)

Select MIRI Cooling: CC vs. CS

Flight SSDesign & Build

Deliver SSTo Observatory

CS

CC

Final ISIMThermalDesign

Final ISIMDesign

TIE5. Pathfinder RadiatorThermal Balance Test

TIEC1. FPE TCSHardware Simulator

TIEC2. FPE Unit LevelDissipation & Stability

Should this go to

ETU ISIM/PF OTE?

Should this go to

ETU ISIM/PF OTE?

ENC1/ENS1/EFG1. ETU Thermal Perf. Test• FPA isolation from housing

• dissipation & stabilityNIR

MIRI

FNC1/FNS1/FFG1. Flight SI Thermal Perf. Test• FPA isolation from housing

• dissipation & stability FMI1. Flight SI Thermal Perf. Test• FPA isolation from housing

• dissipation & stability FMC1. Flight SI & Cooling SystemThermal Performance Test• Cryocooler or Cryostat

Deliver MIRITo ObservatoryPost Test OB7?

TOT2. OTE CoatingsEmissivity TestsAt Cryo Temps

TOT3. PMSA EDUAssembly Conductances,


NGST

Ball

GSFC

SI Mfr

Test Responsibility

NGST

Ball

GSFC

SI Mfr

Test Responsibility

8/03

8/04 11/04

TIS6. Heat Strap / Harness Standoff Test

TIS7. Structure JointConductance Test

TIS8. Harness Test (End to End) Thru Temp Regimes

TIS5. ISIM Coating εat Cryogenic Temp

1/0510/04

TIS1. Strap Development Test

1/04 4/04

TIE4. Radiator Coating- Large Samples

4/04 7/04

TBD TBD

12/039/03

11/02 9/03

12/03 1/04

10/04 1/056/04 9/04

9/03 12/03

10/04 1/05

TBD TBD

TOT4. SMA EDUAssembly Conductances,


1/04 4/04 1/06 4/06

7/06 10/06

ISIM Thermal CDR – 1/05

ISIM Thermal PDR – 1/04

TIS10. Heat Switch& Miscellaneous

Thermal H/W 6/05 9/05

CC1 /CS1. Cooler Thermal Perf. TestCooling performance in 30K env.

TIEC3. FPE TCSFlt H/W Test

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Verification Overview

Developmental – straps, heat switches, relays, harnessing, coatings, materialsComponent – detectors, etc.Radiator/Enclosure½ Scale Hi-Fidelity Sunshield(with OTE/SIM SIM)IECInstrument ETU ISIM – GSFC SESFlight ISIMTelescope Pathfinder – Glen Plumbrook FacilityTelescope with ETU ISIMTelescope with Flight ISIMSpacecraft Bus TB/TB

2004

2011

Confidence in predicted observatory performance must be achieved early in C/D

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PlumbrookTest Chamber

Shop Area

ExperimentAssembly Area

Office Area

ExperimentDisassembly Area

Instrumentation and Control Area Existing 12.2 m shroud

15 m x 15 m dooron both sides

Plum Brook test facility provides the room to conduct a high fidelity

thermal / vacuum environment in which the Observatory Optical

performance is verified

Plum Brook test facility provides the room to conduct a high fidelity

thermal / vacuum environment in which the Observatory Optical

performance is verified

OTE PathfinderOTE/ISIM Flight Article

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Observatory Top Level Heat Flow Map [W]NGST/BATC Original: "Obs Truss v3.1" (+5°)

NGST/BATC Updated: "Obs Truss v3.1a corr" (+5°)

Imposed Load:

Conduction Flows:

Rejected To Space:

0.006

Groups: Instrument Radiator

Detector Radiator

Sunshield ISIM Enclosure

ISIM Structure

Tower/ Isolator

Bus/ Closeout

Instruments DetectorsOTE

18,209 13.8 80,658 29.1 0.9050.917

0.2740.312

0.1520.176

0.137

0.038 0.202

0.007

0.024

0.2700.144

0.957

0.442

0.371

0.013

0.109

0.049

0.036

0.007

3.347 .013

0.054

Radiation Flows:

80,609

0.956

2.5

18,221 0.1530.020 0.144

0.028 0.021 0.0020.115 0.006

0.044 0.1980.263

0.145

0.38548.6

26.4 0.011

0.441

0.118

3.3910.117

0.124 0 0.040

0.281

0.2800.042 0.0120.034

0.0090.0080.001

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Modeling Results

NIR Detector Cooling Margin

0

10

20

30

40

50

60

70

80

Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04 May-04

%

OTE PM Temperature

20304050

60708090

Aug-03 Oct-03 Nov-03 Jan-04 Mar-04 Apr-04 Jun-04

Kel

vin

leading segment

aft segment

avg

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JWST

Documents

JWST Thermal Systems Thermal Design Challenges and Status …safir.jpl.nasa.gov/BeyondSpitzerConf/proceedings/session... · 2004-08-23 · 2 JWST Thermal Systems JWST Mission Overview