The 3 omega transient line method for thermal characterization of superinsulator materials developed for spacecraft thermal control

Matthew Dalton (1) , Ricardo Nadalini (1) , Luca Celotti (1) , Małgorzata Sołyga (1) , Sandrine Berthon-Fabry (2) , Claudia Hildenbrand (2) , Marta Ochoa (3) , Luisa Duraes (4) , Ana Maia (4) , Lorenz Ratke (5) , Barbara Milow (5) , Jessica Laskowski (5)

1 Active Space Technologies GmbH
2 PERSEE - Centre Procédés, Énergies Renouvelables, Systèmes Énergétiques
3 Active Aerogels
4 UC - University of Coimbra [Portugal]
5 DLR Institut für Materialphysik im Weltraum

The 3 Omega Method is a form of the transient line method for thermal characterization that has been in limited use since 1912. Through sinusoidal heating of a thin copper wire located on the specimen and varying the input frequency, a third harmonic voltage arises, the frequency dependence of which carries information about the thermal conductivity and diffusivity of the sample being tested. Thus the heating wire serves also as the sensing element in this method. Major advantages of this approach include very small temperature oscillations, on the order of a few degrees or less, significantly reducing errors arising from thermal radiation and gaseous convection that plague more traditional methods which typically require very large temperature gradients for low conducting materials. Additionally, in this method, thermal conductivity and diffusivity are extracted from the measurement simultaneously based on first principles, eliminating the need for complex and unreliable thermal modelling and calibration of the measurement system. The implementation of this method has been significantly facilitated and its sensitivity and dynamic range improved by the advancement of modern technology, especially the development of lock-in amplifiers and subsequently digital signal processing. Traditionally, this method requires fabrication of micro heating elements through vapour deposition of copper on the specimen to be tested. This method has been implemented at Active Space Technologies GmbH for testing aerogels developed in the context of the AerSUS-Aerogel European Supplying Unit for Space Applications - project FP7 (contract no: 284494), an initiative funded by the Seventh Framework Programme of the European Union. To the best of our knowledge, this is the first time that it has been implemented using macroscopic (60 micro-meter diameter) mass produced copper wire, significantly reducing sample preparation cost and time. Furthermore, this work represents the first use, to our knowledge, of digital signal processing techniques, namely discrete Fourier powers, to extract the third harmonic signal, eliminating the need for large time constant analog circuitry, and making feasible the extremely low frequencies (down to 0.001 Hz) which are required for thermal characterization of super-insulators. We present the implementation of this method, a comparison of results for known materials from the literature and thermal characterizations of super-insulators for space applications. Additionally, simulations and analysis are presented to showcase the use of such super-insulating materials developed by the AerSUS consortium in a realistic Mars lander scenario.

Mots clés: Aerogel; Thermal characterisation; Spacecraft

Domaines: Energétique

Matthew Dalton, Ricardo Nadalini, Luca Celotti, Małgorzata Sołyga, Sandrine Berthon-Fabry, et al.. The 3 omega transient line method for thermal characterization of superinsulator materials developed for spacecraft thermal control. 65th International Astronautical Congress - IAC 2014, Sep 2014, Toronto, Canada. ⟨hal-01113225⟩