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G. Colombatti, A. Francesconi, P.F. Lion Stoppato, M. De Cecco (CISAS "G. Colombo" - UniversitÓ di Padova - Italy), F. Ferri (Space Science Department,ESA/ESTEC,Noordwijk zh, The Netherlands), M. Fulchignoni (UniversitÚ Paris VII /DESPA Obs. Paris-Meudon, France), F. Angrilli (CISAS "G. Colombo" - UniversitÓ di Padova - Italy)
A new design of a platinum resistance sensor has been studied for atmospheric experiments onboard a lander mission in order to measure the vertical temperature profile of the Martian atmosphere. Laboratory tests of different prototypes of platinum resistance thermometers (PRT) have been performed and the results are presented. The prototypes are derived from the HASI TEM, the temperature sensors of the Huygens probe of the Cassini/Huygens mission. To obtain an accurate estimation of the atmospheric temperature gradient, very high spatial resolution measurements are required. This means that, for a given descent profile, a high sampling frequency is needed. Studies have been carried out to improve the sensor performance; they result in new possible structural solutions. In the new design, the sensing element (Pt wire) is suspended on very thin non-metallic fibres truss, in order to thermally decouple it from the supporting structure. Several sensors have been designed and built; laboratory tests have been conducted in a wind tunnel in order to dynamically characterise the sensors. The time response has been investigated and the time constant calculated from the asymptotic trend of the sensor response to a step-wise electric power, simulating a steep temperature gradient. The measurements of the PRT have been compared to those of numerical simulations. A prototype has also flown in a balloon flight test in order to verify its performance in Earth's atmosphere. Results from post flight analysis data of the balloon flight experiment are presented; spectral analysis of the data has evidenced the larger bandwidth of the new sensor and a higher signal to noise ratio. Improvements of HASI TEM performance are shown in terms of a shorter time constant; this allows the new sensor to be able to resolve smaller temperature variations during the descent in Mars' atmosphere.
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