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1 Solar Orbiter EUS: Thermal Design Considerations Bryan Shaughnessy, Rutherford Appleton Laboratory Solar Orbiter EUV Spectrometer Thermal Design Considerations Bryan Shaughnessy

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Solar Orbiter EUV Spectrometer. Thermal Design Considerations Bryan Shaughnessy. Spacecraft Sunshield. Aperture (100mm*100mm). Primary Mirror (100mm*100mm). Baffles. Optical path. Width = 0.3m. Length 1.4 m. Slit Assembly. Grating. Heat Stop. Basic Configuration. - PowerPoint PPT Presentation

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Page 1: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Solar Orbiter EUV Spectrometer

Thermal Design Considerations

Bryan Shaughnessy

Page 2: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Basic Configuration

Detector Assembly

Aperture

(100mm*100mm)

Grating

Length 1.4 m

Width =

0.3m

Slit Assembly

Optical path

Primary Mirror

(100mm*100mm)

Heat Stop

Baffles

Spacecraft

Sunshield

Page 3: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Basic Thermal Requirements

• Detector temperature < -60 deg C (target -80 deg C)• Structure and optics:

– Multilayer coatings (if used) are assumed to be a limiting factor. < 100 deg C assumed at present.

• Thermal Control System Mass TBD• Thermal Control System Power TBD (minimise)

Page 4: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Thermal Environment

Distance From Sun AU

Heat Flux

W/m2

Through

Aperture, W

1.2

1.0

0.9

0.8

0.6

0.4

0.2

951

1370

1691

2140

3805

8562

34250

9.51

13.7

16.9

21.4

38.0

85.6

342.5

Cold case non operational

Hot case non operational

Start Up

Hot Case operational

Cold Case Operational

Page 5: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Solar Thermal Loads at 0.2 AU

350 WThrough Aperture 250 W

200 WAbsorbed at primary

100 W

50 W3 W

103 WAbsorbed at baffles

47 WAbsorbed atheat stop(‘focussed’)

(Absorbing Optics/No Aperture Filter)

Page 6: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Irradiance Profile at Primary Mirror(No Aperture Filter)

35 KW/m2

30 KW/m2

25 KW/m2

20 KW/m2

15 KW/m2

Page 7: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

The Thermal Challenges

• Reject heat input to system of ~350W at 0.2AU– Filter at aperture?– Maintaining sensible temperatures/gradients within instrument– Getting heat to radiators (or to spacecraft cooling system)– Spreading the heat across the radiators

• Prevent heat loss when instrument is further from the Sun– Maintaining sensible temperatures within instrument– Minimising heat transfer to radiators (or to spacecraft cooling

system)– Minimising power required for survival heaters

Page 8: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Heat Rejection by Radiators

• Radiator heat rejection capability a function of:

– Emissivity ~ 0.95 for black paint– Efficiency ~ 0.96– View-factor to space ~ 0.95

• How to transfer heat to radiator?

Radiator (1.4 m x 0.3 m)

Temperature Heat Rejection

K °C W/m2 Watts

233

253

273

293

313

333

343

353

373

-40

-20

0.0

20

40

60

70

80

100

144

200

270

357

461

587

654

734

907

62

87

117

154

200

254

284

318

393

Page 9: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Thermal Design Options

• Solar absorptivity of the optics:– High (i.e., SiC) – remove more heat from primary mirror– Low (e.g., gold coated) – remove more heat from heatstop – but likely restriction

on coating temperature• Coupling to radiators:

– Fitted with heat pipes or loop heat pipes to distribute heat– Primary mirror connected to radiator via thermal straps and/or heat pipe

evaporator.• How to get high thermal conductance coupling?

– Heat loss minimised during cold phases by:• Louvers• Temperature dependent coatings (major development programme required)• Use of loop heat pipes• Use of variable conductance heat pipes

Page 10: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Loop Heat Pipe Concept

Solar load

LHP Evaporator

Radiator (condenser)

Flexible lines

Page 11: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Loop Heat Pipe Concept

•Advantages:•Control over amount of heat removal (reduce when further from Sun)•Flexible couplings allow for pointing of primary mirror

•Technical Challenges: •Selection of working fluid compatible with hot and cold environments

• ammonia: -40 °C →+80 °C• methanol: +55 °C → +140 °C

• Freezing of working fluid in radiator during cold cases?• Thermally coupling the primary mirror to the evaporator • Redundancy?

• multiple lines to same evaporator, multiple evaporators?

Page 12: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Thermal Model Predictions

Radiator Area, m2 T, deg C Radiator Area, m2 T, deg C Baffle 0.2 105 0.4 48 Primary 0.1 105 0.2 46 Heat stop 0.02 33 0.02 15 Detector 0.1 -80 0.1 -80 TOTAL 0.22 - 0.72 - Width* 0.16m - 0.51m - * assuming 1.4 m instrument length

(Absorbing Optics/No Aperture Filter/Heat pipes or loop heat pipes to radiators)

Page 13: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

Detector Cooling

• Aluminium filtering blocks any remaining solar thermal loads

• Detector fitted in a thermally isolated enclosure:– Low emissivity shielding– Low conductivity mounts

• Dedicated radiator attached to detectors via a cold finger– Multistage to shield thermal loads from spacecraft sunshield?

• Electric heaters fitted for temperature control and outgassing operations

Page 14: Solar Orbiter EUV Spectrometer

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Solar Orbiter EUS: Thermal Design ConsiderationsBryan Shaughnessy, Rutherford Appleton Laboratory

THE END