Proc. SPIE. 10565, International Conference on Space Optics — ICSO 2010
KEYWORDS: Digital signal processing, Aerospace engineering, Fiber Bragg gratings, Sensors, Fiber optics sensors, Semiconductor lasers, Space telescopes, Signal processing, Astronomical imaging, Temperature metrology
We present our work about the development of two complementary interrogation schemes based on fiber optic sensing for the use of structural and thermal monitoring of Ariane launchers. The advantages of fiber optic sensing in particular light-weight, immunity to electromagnetic interferences and the possibility of sensor distribution along optical fibers are driving factors for utilization of this technology in space crafts . The edge-filter (EF) and scanning-laser (SL) interrogators for determination of the mean wavelength of fiber Bragg grating (FBG) sensors have been implemented as two separate demonstrators. Within this paper we describe the functional principles of both interrogators. Furthermore we present test results where the developed systems have been used for readout of FBG sensors which are implemented in an Ariane structural demonstrator during thermal, thermal-vacuum and vibration tests. Functionality of both systems is demonstrated and their potential for further development towards space qualified systems is shown.
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.
Within an ESA funded project combustion chambers of Ariane V rockets are investigated for further development. Due
to temperature gradients of approximately 1300 K/mm in the combustion chamber during launch, material damages
occur because of the Doghouse effect. To avoid these damages, the combustion chambers have to be redesigned
wherefore the occurring temperatures have to be measured with an uncertainty of ±5 K. In order to measure the
temperature in the small layer between the hot exhaust emissions and the coolant, optical fiber sensing is deployed.
Embedding special optical sensor fibers that are high temperature resistant within the material allows measuring the wall
In order to demonstrate fiber optic sensing for high temperature and strain measurement, Thermo Mechanical Fatigue
(TMF) panels, constructed as sandwich structure have been developed that represent the combustion chamber walls.
Coated fibers which are installed in the the panel can be subjected to thermal loads up to 1000 K inside a high
temperature oven. Online measurements of FBG sensors inscribed in the embedded optical fibers can be carried out. The
measurement results of the FBG sensors exactly match the data of the electrical reference sensor.
For FBG readout we use our newly developed Scanning Laser (SL) Interrogation System which uses a tuneable laser
source. The output wavelength is determined by a set of control currents. In order to archive the required accuracy a
Current Control Unit (CCU) stabilizes the control currents and thereby the output wavelengths. The CCU significantly
improves the accuracy and additionally enhances the measurement rate. The high temperature measurement results
demonstrate compatibility with the requirements.