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

2. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 2 Summary Progress and current status –Developing thermal design concepts for trade-off Thermal Background Thermal Concepts Conclusions

3. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 3 Basic Configuration Aperture (approx 100mm*100mm) z -X Grating Detector Assembly Height = 0.108 m Length 1.4 m Width = 0.31m Slit Assembly Optical path Primary Mirror (100mm*100mm) Heat Stop

4. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 4 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)

5. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 5 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)

6. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 6 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.

7. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 7 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) TemperatureHeat Rejection KCW/m2Watts 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

8. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 8 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

9. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 9 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

10. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 10 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

11. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 11 Detector Thermal Control Internal VDA Detectors Detector Supports (isolation) Thermal Screen Low K (mylar) High K (Aluminium) Anodized Detectors MLI Strap to Radiator with heater

12. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 12 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)

13. Solar Orbiter EUS: Thermal Design Progress Bryan Shaughnessy, Rutherford Appleton Laboratory 13 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