Complementary Techniques for the Accelerometric Environment Characterization of Thermodiffusion Experiments on the ISS

The accelerometric environment of IVIDIL and DCMIX experiments were successively monitored not only to identify the main disturbances that could affect the experiments but as well to ensure the correct interpretation of the experimental results. To do so, the conventional techniques used by NASA have been complemented by new tools developed and adapted to help the surveillance of the runs. A summary of these main new techniques is presented further. To show the potentiality of all these techniques, moderate and strong disturbance episodes such as berthings, dockings and reboostings were analyzed by using acceleration signals that came from three different sensors located in the Destiny, Columbus and JEM/Kibo modules, respectively. The first technique proposed is based on the Shannon entropy concept in both time (TEN) and frequency (SEN) domains. It has been found, that SEN technique is a fast and easy tool to detect the different disturbances registered throughout the experiments. The second technique suggested by the authors is based on the one-third octave frequency band RMS values and is called RMS warning map. It is a visual tool which was demonstrated to be very efficient in detecting the range of the frequencies that surpasses the ISS limits requirements, especially when a sudden disturbance occurs. Finally, in order to identify nonlinearities in the frequency domain within a signal, bispectrum and trispectrum functions have been applied. Quadratic and cubic phase couplings have been detected with these techniques only between high frequencies and especially for the signals coming from JEM/Kibo module.