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

Solar Orbiter EUV Spectrometer

Thermal Design Progress

Bryan Shaughnessy

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

Summary

• Progress and current status

– Developing thermal design concepts for trade-off

• Thermal Background• Thermal Concepts• Conclusions

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

Basic Configuration

Aperture (approx 100mm*100mm)z

-X

Grating

Detector AssemblyHeight = 0.108 m

Length 1.4 m

Width =

0.31m

Slit Assembly

Optical path

Primary Mirror

(100mm*100mm)

Heat Stop

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

Initial 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 < 3.5 kg• Thermal Control System Power TBD (minimise)

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Solar Orbiter EUS: Thermal Design ProgressBryan 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

(Excludes solar input from outside of the observed region)

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

The Thermal Challenges

• Reject heat input to system of ~340W at 0.2AU– Maintaining sensible temperatures within instrument– Getting heat to radiators– 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– Minimising power required for survival heaters

• Overall challenge: achieving the above with sensible mass/power budgets.

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

Radiator Surface Area

• Heat output via radiator(s) mounted on the +Z surface

• Radiator heat rejection capability a function of:– Emissivity ~ 0.95 for z306

black paint

– Efficiency ~ 0.96

– View-factor to space ~ 0.95

Radiator (1.4 m x 0.31 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

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

Basic Thermal Concept

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

restriction on coating temperature• Coupling to the main radiator:

– Various options being considered in the thermal trade-off– Fitted with heat pipes or loop heat pipes to distribute heat– Primary mirror and structure connected to radiator via thermal straps and/or

heat pipe evaporator. Development programme needed to attached heat pipe evaporators to SiC structure or optics.

– 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

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

Loop Heat Pipe / Absorbing Optics Concept

~ 340W

LHP Evaporator

Primary Mirror at ~ 100 – 120 deg C

Radiator (~1.4 m x 0.31 m) at ~ 80 deg C

Technical Challenges: •Selection of working fluid compatible with hot and cold environments (ammonia: -40C →+80C; methanol: +55C → +140C)•Thermally coupling the primary mirror to the evaporator

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

Basic Thermal Concept (cont)

• Detectors:– Dedicated radiator attached to detectors via a cold finger

– Detector fitted in an enclosure to thermally isolate it from the warm structure

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

Detector Thermal Control

Internal VDA Detectors

Detector Supports (isolation)

Thermal Screen

Low K (mylar)

High K (Aluminium)

AnodizedDetectors

MLIStrap to Radiator with heater

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

Conclusions

• The EUS instrument presents an extremely challenging thermal design problem

• Work is ongoing to investigate a number of thermal design options

• Initial indications are that the mass of the thermal control system will exceed 3.5 kg (e.g., radiators, heat pipes, heaters, redundancy, etc)

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

Future Work

• Consider options for reducing heat load into the instrument, e.g.– Shutter– Instrument rastering– Filters

• Complete trade-offs and identify potential thermal designs (together with mass budgets, margins, hardware/suppliers, development programmes, etc)

• Identify if a spacecraft level thermal control system should be considered