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The small debris impact dynamic was detected and monitored with Fiber Bragg Gratings (FBG) sensors at very fast acquisition frequencies, up to 0.5 GHz (2 ns), measuring the variation of the total reflected signal by the FBG. The acquisition system is based on commercially available products. To measure the total wavelength spectrum, the fastest available spectrometer can go up to 2 MHz acquisition (Micron-Optics), which is insufficient to detect the hypervelocity impact. The impact pressure evolution of the FBG, placed in the middle layer, was compared with commonly used strain gauges placed a few layers further or on the back of the last layer. The measured impact time delay and relative intensity were compatible between the two sensing methods.
Some samples were characterized in details using the X-ray Computed Tomography at ESTEC, they permitted us to confirm the results by observing the details of the healing and follow the impact trajectory visually.
To sum up, this contribution shows how WDM optical beamforming architectures can be simplified combining dispersive and non-dispersive time delays to allow the use of photonic beamforming techniques in large antenna arrays. The number of optical sources of the beamformer, as well as its total size and cost, can be highly reduced using this technique. Experimental results validating the feasibility of the technique are provided.
This work presents the activities performed and the lessons learnt in the frame of ESA’s ARTES-5 project “Fiber Optic Sensing Subsystem for Spacecraft Health Monitoring in Telecommunication Satellites”. This project finished in July 2009, with the implementation and testing of two different demonstrators employing FBG sensor technology: FBG sensors for temperature monitoring in high voltage environments, and in particular in several parts of electric propulsion subsystems [1], and FBG sensors for thermal monitoring of array-antennas during RF testing [2].
In addition, the contacts performed with different actors within the space community allowed the identification of a special area of interest for the substitution of regular thermocouple instrumentation by FBG technology for thermal vacuum ground testing of satellites.
Since the performance characteristics of the two systems are different from each other, they are dedicated for different sensing applications on a launcher. The EF sensor interrogator provides a sample rate of 20 kHz at a number of 4 connected sensors and supports parallel readout and aliasing free operation. Therefore it is best suited for high priority measurement. Structural monitoring which requires the acquisition of real time sensor information in order to support control of the launcher is one operation area for a future EF system. The SL interrogator provides an overall measurement rate of 1 kHz at a number of 24 connected sensors distributed on three sensor channels. It can be adapted to any sensors that have design wavelengths lying within the output spectrum of the laser diode. Furthermore the number of overall sensors to be read out with this system can be adapted easily. Thermal mapping of satellite panels is one possible future application for the SL interrogator.
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