Appendix H. The challenges of modelling helium gas conduction and helium seal interfaces in ESATAN-TMS r7. Nicole Melzack (RAL Space, United Kingdom)

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1 93 Appendix H The challenges of modelling helium gas conduction and helium seal interfaces in ESATAN-TMS r7 Nicole Melzack (RAL Space, United Kingdom)

2 94 ESATAN-TMS r7 Abstract The Meteosat series of spacecraft are meteorological satellites, providing a range of data that inform weather forecasts across Europe. Two instruments going on the MTG (Meteosat Third Generation) satellites will be calibrated using the blackbody targets that are being designed at RAL Space. Modelling of the ground based blackbody calibration targets was done in ESATAN-TMS r7. The targets use a helium gas gap heat switch as the main aspect of the thermal control system. This talk will cover the challenges involved in modelling the gas conduction, and will present the current implementation. Other aspects of the design, such as determining the conductance across a complex interface involving a helium seal will also be discussed. This presentation will also touch on the correlation of the thermal model post prototype testing.

3 ESATAN-TMS r7 95 The challenges of modelling helium gas conduction and helium seal interfaces in ESATAN-TMS r7 Nicole Melzack, RAL Space, STFC European Space Thermal Analysis Workshop 5-6 th October 2016 Outline Meteosat Blackbodies Design overview Thermal challenges Helium Conduction Helium seal interface Next steps

96 ESATAN-TMS r7 Meteosat MFG 1979 2011 MSG

( Flexible Combined Imager) by TAS-F Two sets

4 96 ESATAN-TMS r7 Meteosat MFG MSG MTG Image credit: ESA Image credit: ESA Image credit: Eumetsat MTG MTG-S IRS (Infra-red Sounder) by OHB MTG-I FCI ( Flexible Combined Imager) by TAS-F Two sets of customer requirements One calibration blackbody design

ESATAN-TMS r7 97 Blackbody calibration target Target of accurately known temperature and high (~1) emissivity Precisely controlled Better than instrument can measure Used to calibrate instrument

5 ESATAN-TMS r7 97 Blackbody calibration target Target of accurately known temperature and high (~1) emissivity Precisely controlled Better than instrument can measure Used to calibrate instrument Often a baseplate surrounded by a baffle Calibration blackbody MTG blackbodies thermal challenges Large operating temperature range K Small temperature gradient requirements Transition between temperatures in 0.1 K steps Transition 16 K in 30 minutes 3 kw power limit

pressure of the gas R is the specific gas constant α is the thermal accommodation factor Equation from: Active-mirror-laser-amplifier thermal

6 98 ESATAN-TMS r7 Helium gas gap Cavity Heaters Helium conductivity in a gas gap Helium thermal conductivity in a helium gas gap k T = k bulk T k bulk T T e p 3 R T 1 α α k bulk is the bulk conductivity of He T is temperature e is the gap thickness p is the pressure of the gas R is the specific gas constant α is the thermal accommodation factor Equation from: Active-mirror-laser-amplifier thermal management with tuneable helium pressure at cryogenic temperatures, A. Lucianetti et al., Optics Express, Vol 19, Issue 13, pp , 2011.

7 Conductivity (W/mK) ESATAN-TMS r7 99 Helium pressure and thermal conductivity He Pressure (bar) Main thermal modelling challenges Helium conductivity Helium seal interface

8 100 ESATAN-TMS r7 Helium gas conduction modelling CAVITY k A GL1= x k A GL2= x LN 2 Helium gas conduction in ESATAN

9 ESATAN-TMS r7 101 Helium gas conduction in ESATAN Three He pressure set points needed

10 102 ESATAN-TMS r7 Helium conduction limitations of equation Temperature of helium Perpendicular conduction modelled only Gas gap modelled O(1mm) much larger than conventional gas gaps Larger surface area than a conventional gas gap heat switch Curved surface Dynamic helium gas conduction

11 ESATAN-TMS r7 103 Helium gas conduction modelling CAVITY k A GL1= x k A GL2= x LN 2 Breadboard Model Testing

12 104 ESATAN-TMS r7 Helium conduction from testing Main thermal modelling challenges Helium conductivity Helium seal interface

13 ESATAN-TMS r7 105 Helium seal interface Helium seal interface Stainless steel ring Al cavity Stainless steel LN2 jacket M10 screw Helium seal

14 106 ESATAN-TMS r7 Helium seal interface Dummy seal interface

15 ESATAN-TMS r7 107 Dummy seal interface Stainless steel ring Al cavity M10 screw Stainless steel LN2 jacket heater Helium seal Dummy seal interface M10 screw Stainless steel ring Helium seal Al cavity Stainless steel LN2 jacket

16 108 ESATAN-TMS r7 Next steps Using model to improve bulk temperature changes Modelling transient helium assisted cooldowns Performing helium seal test Verifying the conductive path through the interface, and correlating model further with findings Thank you Nicole Melzack, RAL Space, STFC Tel: European Space Thermal Analysis Workshop 5-6 th October 2016

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