1,721,109 research outputs found
Design and testing of a roto-translational shutter mechanism for planetary operation
No full textThis work describes the design and testing of a shutter mechanism for a miniaturized infrared spectrometer developed for the ESA ExoMars Pasteur mission. Unlike most usual cover mechanisms, the conceived one provides a roto-translational motion. This feature allows the sealing of the interferometer main entrance window from dust contamination, in addition to the usual function of shuttering the instrument field of view. Although this characteristic is strongly desired because it avoids dust deposition and optics contamination while the instrument is not operating, it makes the mechanism design significantly more complex. Moreover, challenging design constraints were faced: the mass budget allowed for no more than 30 g allocation, the expected working thermal range extended down to -80 C and high vibration levels with an acceleration peak of 670 m/s2 were predicted during Mars landing. To complete the picture, the mechanism cover was required to provide also a calibration target for the 2-25 μm spectral range of the spectrometer. The resulting system is made by a calibrating/shutter cover moved by a purposely designed out of plane cams system which provides the desired motion. A mechanism mockup was assembled and successfully tested in the predicted thermal and mechanical environments. © 2013 IAA Published by Elsevier Ltd. All rights reserved
Compensation of Thermal Gradients Effects on a Quartz Crystal Microbalance
Full text linkQuartz Crystal Microbalances (QCM) are widely used instruments thanks to their stability, low mass, and low cost. Nevertheless, the sensitivity to temperature is their main drawback and is often a driver for their design. Though the crystal average temperature is mostly considered as the only disturbance, temperature affects the QCM measurements also through the in-plane temperature gradients, an effect identified in the past but mostly neglected. Recently, it has been shown that this effect can prevail over that of the average temperature in implementations where the heat for thermal control is released directly on the crystal through deposited film heaters. In this study, the effect of temperature gradients for this kind of crystal is analyzed, the sensitivity of frequency to the average temperature gradient on the electrode border is determined, and a correction is proposed and verified. A numerical thermal model of the QCM has been created to determine the temperature gradients on the electrode borders. The frequency versus temperature-gradient function has been experimentally determined in different thermal conditions. The correction function has been eventually applied to a QCM implementing a crystal of the same manufacturing lot as the one used for the characterization. The residual errors after the implementation of the correction of both average temperature and temperature gradients were always lower than 5% of the initial temperature disturbance. Moreover, using the correlation between the heater power dissipation and the generated temperature gradients, it has been shown that an effective correction strategy can be based on the measurement of the power delivered to the crystal without the determination of the temperature gradient
A new data processing method for space-borne Fourier Transform Spectrometers
No full textOne of the main limitations of Fourier Transform Spectrometers (FTS) is represented by their sensitivity to vibrations, which in general leads to a reduction of the Signal to Noise Ratio (SNR) and may generate ghosts of spectral features tricky to detect. A possible implementation to mitigate such errors is to exploit correction algorithms that allow obtaining signals sampled at constant optical path steps by processing data sampled at high frequency. In this work, a new processing method is presented, based on the arccosine method and exploiting two reference signals in the quadrature phase. Performances of the proposed method are compared to those of other algorithms by comparing an index expressing the distortion spectral lines
Long-term vibration monitoring onboard Mars Express mission
No full textThis work describes mechanical vibration monitoring onboard the ESA Mars Express orbiter, in a period of eight years since the spacecraft commissioning. The vibrations are measured using the planetary Fourier spectrometer, an infrared spectrometer based on a modified Michelson interferometer, which is part of the mission payload. The instrument is very sensitive to thermomechanical inputs, and the mechanical vibrations are a source of disturbance for its scientific measurements. However, the instrument sensitivity to mechanical disturbances and the exploitation of a diagnostic mode provide a chance to monitor the vibration environment onboard the spacecraft. It has been assessed that the main vibration contributions derive from the reaction wheels and the laser ring gyroscopes that implement harmonic dithering. Spacecraft acceleration levels at the instrument mounting interface are provided with the aim of defining reference figures for engineers and scientists who have to cope with a usually unknown in-orbit vibration environment. Moreover, the vibration levels evolution along the mission lifetime is analyzed to highlight the effect of the spacecraft aging in that respect
Measurement of stress waves propagation in percussive drilling
Full text linkThis work describes the results of a test campaign aimed to measure the propagation of longitudinal, torsional, and flexural stress waves on a drill bit during percussive rock drilling. Although the stress wave propagation during percussive drilling has been extensively modeled and studied in the literature, its experimental characterization is poorly documented and generally limited to the detection of the longitudinal stress waves. The activity was performed under continuous drilling while varying three parameters, the type of concrete, the operator feeding force, and the drilling hammer rotational speed. It was found that axial stress wave frequencies and spectral amplitudes depend on the investigated parameters. Moreover, a relevant coupling between axial and torsional vibrations was evidenced, while negligible contribution was found from the bending modes. A finite element model of the drill bit and percussive element was developed to simulate the impact and the coupling between axial and torsional vibrations. A strong correlation was found between computed and measured axial stress spectra, but additional studies are required to achieve a satisfactory agreement between the measured and the simulated torque vibrations
Non-contact techniques for the quality analysis of PET bottles
No full textThis work was motivated from finding a complementary way of tuning and controlling the machine parameters of Injection Stretch Blow Molding process. In the current approach, a specialized technician detects the bottle defects by visual inspection and corrects the machine parameters using its own experience or indications obtained by previous statistical analyses. As all human based operations, inherent limitations are that the results are influenced by the operator skills; in addition, the experience can be hardly converted into a database, which could be used for the process optimization. The solution investigated in this work is to replace visual inspection with an image processing system. A prototype for offline analyses of PET bottles was designed in order to have a resolution allowing to identify the most common bottle defects. The acquired images were analyzed with algorithms implemented in LabVIEW. Results showed that this system can off-center gate, haze and pearlescence with a repeatability and reproducibility sufficient for the identification of bottles with manufacturing defects
Apparent mass distribution at the feet of standing subjects exposed to whole-body vibration
No full textThis study was carried out to investigate the influence of the body posture and of the foot support on the apparent mass distribution at the feet of standing subjects exposed to whole-body vibration. The apparent mass was measured at the driving point through a capacitive pressure sensor matrix, which allowed to separate the contributions of the different foot regions. The overall value was also determined using a conventional measurement system based on piezoelectric load cells. Ten male subjects performed 15 tests with three kinds of feet supports (flat rigid, anatomic rigid and flat soft) in five different postures. Static components of the pressure measurements were exploited to identify which fraction of the weight is supported by the rearfoot, the midfoot and the forefoot in the various test configurations. Factorial design of experiments on different response variables showed that the apparent mass is affected by the posture but not by the type of feet contact surface; conversely, the presence of insoles varies with the apparent mass distribution on the different feet parts. Practitioner Summary: The response of standing subjects to whole-body vibration has always been considered as a global parameter measured at the driving point, neglecting the local phenomena occurring in different foot parts. We have experimentally identified the apparent mass distribution of subjects in different standing postures and with different foot supports. © 2013 Copyright Taylor and Francis Group, LLC
Thermo-mechanical design feasibility study of an Imaging Spectrometer for the Jovian system
No full textThe Moons And Jupiter Imaging Spectrometer is an experiment designed for the Jupiter Icy Moons Explorer ESA mission. The instrument will perform imaging spectroscopy in the visible and near infrared ranges to study the Galilean System. This work focuses on the thermo-mechanical design study performed to assess the instrument feasibility. The thermal design is based on a completely passive cooling, providing operational temperatures lower than 90 K, for the infrared detector, and lower than 140 K for the optical bench. These are required to reduce detector noise and background radiation disturbances on the measured signals. The instrument is mounted on a spacecraft whose temperature during operation is between -10 to 20 °C. Therefore, structural design is driven by the requirement of minimizing the thermal conductance of the instrument supporting structure, which, on the other hand, has to provide strength and stiffness required to hold the instrument optical head and radiators. Different mechanical and thermal layouts have been studied and compared. All the conceived configurations allow achieving the expected design requirements although with different margins with respect to the imposed constraints. © 2014 IEEE
Smart Solar Panels for Space Applications
No full textThe Photovoltaic (PV) Solar Panels are the key technology for the generation of electric energy in space environment. In order to maximize the efficiency of the PV solar panels, two aspects of this technology can be improved: keeping the solar panels surface orthogonal to the direction of the Sun light and cleaned from the deposition of dusts and other contaminants that can absorb a quota of the incoming solar irradiance. The present paper reports the preliminary design of a system of Smart Solar Panels (SSPs) that represents an improvement of PV solar panels aimed to be implemented specifically in space environment. To maximize the produced energy of a solar panel, it has to be kept oriented toward the Sun and with its sensitive surface very clean, without the presence of contaminants. In order to obtain this goal in an autonomous way, the solar panels shall be provided with robotic functionalities to move the panels according to the relative movement of the Sun and to remove the contaminants deposited on the surface as well. Combination of these two functionalities and the adopted solutions, aimed expressly for space application, are the novelty of this work. The SSPs find their application in fixed solar power plant or mobile installation (e.g. lander and rovers) for the exploration of Solar System bodies, primarily the Moon and Mars, but have also a positive impact for terrestrial sites located in desert or mountain areas, where maintenance operations are difficult. The concept has been submitted to the 'call for ideas' for the ESA European Large Logistics Lander (EL3)
About the dynamic characterization of micro-bolometric infrared cameras
No full textThis work describes two methods for the dynamic characterization of a microbolometer infrared camera. The time constant, parameter commonly used for microbolometers dynamic performance identification, has been addressed in literature with studies mainly focused on theoretical computation and only seldom supported by testing activity. In this paper, alternative methods for the dynamic characterization of infrared sensors are presented and related uncertainty budgets are assessed. The infrared camera NEC TH7102WX has been tested with the proposed methods and results have been compared. The microbolometer behavior has proved to strongly deviate from the common first order model so that the time constant is no more a characterizing parameter. Depending on the definition of "equivalent time constants", the measured parameters changed by more than 50%, with values ranging between 30 and 50 ms
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