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SMV-2022-10: CRYSA project – CRYostat Straps for the Athena space telescope
Frolec, Jiří
The goal of the project, from the point of view of the Cryogenics and Superconductivity group at the Institute of Scientific Instruments of the Czech Academy of Sciences (ISI Brno), resides in a cooperation with OHB Czechspace and the Institute of Physics of Materials of the CAS (IPM) in order to select and experimentally measure the properties of materials suitable for mounting a device at a very low temperature (cryostat straps), which will be part of the upcoming Athena space telescope of the European Space Agency (ESA). The project consortium will conduct a survey of available materials and, based on this review, will select two most suitable and commercially available materials, which will be later tested in individual CAS institutes. Materials must meet two basic properties – high mechanical stiffness and low thermal conductivity. Members of the Cryogenics and Superconductivity group at ISI Brno will perform, with the help of special equipment and cooling using liquid helium bath, thermal conductivity measurements and the exposure of selected materials to low temperatures for next mechanical tests at the IPM. The outputs of this project will help ESA with the selection of the optimal material for the construction of the straps supporting the given Athena cryostat.
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SMV-2022-09: Special coatings for a radio-frequency absorber
Frolec, Jiří
As part of the upcoming mission of the European Space Agency, the space-probe JUICE, the task of the Max Planck Institute for Solar System Research is to determine the thermal radiation properties of the coatings intended for the radio-frequency absorber of this probe. In frame of this project, there was an experimental verification of the relative rate of thermal radiation emission, so-called emissivity, of two different coatings deposited on the surface of the developed samples. The main output of the research is the low-temperature tests of these samples carried out using a unique measuring apparatus, cooled by a bath of liquid helium. The emissivity of thermal radiation of both surfaces was determined in the temperature range from 20 K to 300 K. As part of the project, we also assessed, in addition to the thermal-radiative properties, the mechanical stability of the sample at low temperatures. All data have been submitted to the Max Planck Institute in the form of research reports.
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SMV-2022-08: Methods of thermal radiation measurements
Frolec, Jiří
The research activity was focused on experimental methods for testing the relative rate of materials to emit or absorb thermal radiation, i. e. emissivity and absorptivity. The main output is a review of available methods, with an emphasis on those operated at low temperatures. The ordering party's goal is to build dedicated workplace capable of performing the mentioned type of measurements. For this purpose, it was necessary to create an overview of the methods and assess the optimal one for the given purpose. The required research was carried out by members of the Group of Cryogenics and Superconductivity from ISI Brno, based on the available literature as well as on theoretical and practical experience gained during two decades of experiments with their own cryogenic apparatus for measuring thermal radiation interacting with various materials.
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SMV-2022-07: Cryogenic tests of aluminium foils with low emission and absorption of thermal radiation
Frolec, Jiří
The research was focused on the heat transfer by thermal radiation, specifically the interaction of thermal radiation with several different types of aluminium foils, used mainly in the so-called multilayer insulation (MLI). From the supplied raw material, samples suitable for testing were fabricated at the ISI Brno and then examined according to the requirements of the company. We focused on the temperature dependence of the relative ability of the samples to emit or absorb thermal radiation at all wavelengths and in all directions. The experimental verification then took place in a dedicated apparatus cooled by a liquid helium bath for a temperature range from about -253 °C to room temperature, which required choosing an optimal configuration of the apparatus and verifying its calibration. After the individual measurements, the received data were processed, the temperature stability of the foils at low temperatures was evaluated and their thermal-radiation properties were compared with our own low-temperature database of cryogenic measurements. The project contributed to selection of the optimal foil for the intended application, i. e. for use in MLI.
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SMV-2022-06: Thermal radiation of space probes components
Frolec, Jiří
As a part of the upcoming project ARIEL of the European Space Agency, the ordering party Admatis Ltd. needed to determine the temperature dependence of the relative rate of thermal radiation of six different thermoregulatory coatings intended for some external surfaces of the space probe ARIEL. Coatings were tested using a special dedicated method, operating in a liquid helium bath, for temperature interval from approximately -253 °C up to room temperatures. During the cryogenic tests, the character of the total hemispherical radiation of the given layers at all wavelengths was determined. As part of the research, the interpretation and comparison of the measured data was also carried out, based on our experience and using our unique low-temperature database of cryogenic measurements. The results will help the ordering party to select a layer with optimal thermal properties for the given application.
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Low-temperature emissivity of thin Al2O3 layers deposited on copper substrate
Frolec, Jiří ; Králík, Tomáš ; Nyman, L. ; Pudas, M. ; Kallio, E.
Copper is commonly used in cryogenic systems due to its high thermal and electrical conductivity along with excellent solderability. Very low emissivity values of copper surface also reduce in cryogenic systems heat load transferred by thermal radiation. These values may be, however, enhanced by a prospective coating, deposited usually in order to prevent chemical changes on highly reactive copper surface. This paper focuses on protective layers of Al2O3 with thicknesses up to 28 nm, deposited on polished copper. We measured total hemispherical emissivity at cryogenic temperatures before and after the coating process. Contribution of Al2O3 layer to original copper emissivity increased with rising temperature of the layer and with the layer thickness. However, emissivity of the coated copper stayed below 2%, allowing usage of the coated copper in systems where low heat load by thermal radiation is needed. Preliminary tests with oxygen plasma shows that deposited layers can effectively protect the copper surface against oxidation and maintain the original thermal-radiative properties.
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SMV-2021-25: Degree of thermal radiation emission by special layers for space applications
Frolec, Jiří
The subject of the contract research was the analysis of the relative ability of thermal radiation in the entire present electromagnetic spectrum of special surfaces, which will be used by the European Space Agency as heat radiators for the Athena satellite. In cooperation with the ordering party, two pairs of samples have been designed and manufactured, each pair with different highly-emissive coating. An aluminium alloy was used as the base substrate. The so-called total hemispherical emissivity in the temperature range from 20 K to 320 K was measured individually for each sample, using our dedicated cryogenic apparatus. In the frame of this contract, we have also provided our expert opinion and comparison with data from our own database in order to help interpret the obtained results.
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SMV-2021-24: Emissivities of multilayer reflective foils and highly absorptive coatings with different morphology
Frolec, Jiří
This contractual research dealt with materials of very different ability to emit thermal radiation. First project was focused on aluminium-based multilayer foils designed for high reflection of incident light. In the second project we have studied special highly emissive coatings prepared by two different companies. The goal was to determine total hemispherical emissivity of each sample at required temperatures. In the case of the highly emissive coatings the ordering party´s goal was also to evaluate the influence of morphology on the final emission of thermal radiation. Namely, we have tested flat, pyramidal and grooved surfaces with each of the mentioned coatings. This unique research required special shape of samples, modification of the dedicated method for measurement emissivities and absorptivities at cryogenic temperatures and also new calibration procedure and data evaluation. For the first time we used a shielding collar, newly designed and developed in our lab, to cover the circumference of the sample discs and prevent leak of part of the measured thermal radiation. This research extended our knowledge in the field of impact of surface morphology on thermal radiation emission.
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SMV-2021-23: Low-temperature emission of electromagnetic radiation by a special coating intended for a space probe
Frolec, Jiří
This contractual research was focused on emission of thermal radiation by a special coating, which will be applied on part of the surface of JUICE space probe to ensure optimal heat management of the instrument. In cooperation with the ordering party, two samples, deposited by a special coating with different thickness, were designed and fabricated. Goal of the project was to evaluate the total hemispherical emissivity in wide temperature range from 20 to 300 K. The results will help the ordering party to choose optimal thickness of the surface coating to be used for the probe.
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