Solar%20Orbiter%20EUV%20Spectrometer

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Solar Orbiter EUV Spectrometer

• Thermal Design Progress
• Bryan Shaughnessy

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Summary

• Progress and current status
• Developing thermal design concepts for trade-off
• Thermal Background
• Thermal Concepts
• Conclusions

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Basic Configuration
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Initial Thermal Requirements

• Detector temperature lt -60 deg C (target -80 deg
  C)
• Structure and optics
• Multilayer coatings (if used) are assumed to be a
  limiting factor. lt 100 deg C assumed at present.
• Thermal Control System Mass lt 3.5 kg
• Thermal Control System Power TBD (minimise)

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Thermal Environment
(Excludes solar input from outside of the
observed region)
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
Cold Case Operational
Hot Case operational
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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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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) Radiator (1.4 m x 0.31 m) Radiator (1.4 m x 0.31 m) Radiator (1.4 m x 0.31 m)
Temperature Temperature Heat Rejection 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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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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Loop Heat Pipe / Absorbing Optics Concept

• 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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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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Detector Thermal Control
Internal VDA
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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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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