For over two decades the European Space Agency has investigated the possibility of using fiber optic sensors in spacecraft engineering as tools to advance the monitoring and control of spacecraft. The applications have been diverse covering both launcher and satellite applications and encompassing environments from cryogenic to high temperature re-entry applications. The aim of this review is to capture the history and status of fiber optic sensors for space applications demonstrating the breadth of applications that have been studied and the lessons learnt along the way. Finally, it is the intention of this review to look forward, pointing to how this technology can be used in the future and identifying what are the key remaining challenges to its further successful exploitation.

Recently optical sensing solutions based on fiber Bragg grating (FBG) technology have been proposed for temperature monitoring in telecommunication satellite platforms with an operational life time beyond 15 years in geo-stationary orbit. Developing radiation hardened optical interrogators designed to be used with FBG sensors inscribed in radiation tolerant fibers offer the capabilities of multiplexing multiple sensors on the same fiber and reducing the overall weight by removing the copper wiring harnesses associated with electrical sensors. Here we propose the use of a tunable laser based optical interrogator that uses a semiconductor MG-Y type laser that has no moving parts and sweeps across the C-band wavelength range providing optical power to FBG sensors and optical wavelength references such as athermal Etalons and Gas Cells to guarantee stable operation of the interrogator over its targeted life time in radiation exposed environments. The MG-Y laser was calibrated so it remains in a stable operation mode which ensures that no mode hops occur due to aging of the laser, and/or thermal or radiation effects. The key optical components including tunable laser, references and FBGs were tested for radiation tolerances by emulating the conditions on a geo-stationary satellite including a Total Ionizing Dose (TID) radiation level of up to 100 krad for interrogator components and 25 Mrad for FBGs. Different tunable laser control, and signal processing algorithms have been designed and developed to fit within specific available radiation hardened FPGAs to guarantee operation of a single interrogator module providing at least 1 sample per second measurement capability across >20 sensors connected to two separate optical channels. In order to achieve the required temperature specifications of ±0.5°C across a temperature range of -20°C to +65°C using femtosecond inscribed FBGs (fs-FBG), a polarization switch is used to mitigate for the polarization dependent frequency shift (PDFS) induced from fs-FBG which could be in the order of > 20 pm causing > 2°C error in the measurement. Also special transducers were designed to isolate the strain from the FBGs to reduce any strain influence on the FBG temperature measurements while ensuring high thermal conductivity.In this paper we demonstrate the operation of an optical FBG interrogator as part of a hybrid sensor bus (HSB) engineering model system developed in the frame of an ESA-ARTES program and is planned to be deployed as a flight demonstrator on-board the German Heinrich Hertz geo-stationary satellite.

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In this paper the concept and design of the Hybrid Sensor Bus (HSB) system for telecommunication satellites is presented. The HSB development in the frame of an ESA-ARTES project has been started in 2011 and the system will be tested as flight demonstrator onboard the German Heinrich Hertz communication satellite (H2Sat) in 2016.In state-of-the-art telecommunication platforms hundreds of sensors are necessary for satellite control and monitoring. The sensors are wired point-to-point (p2p) to the satellite management unit (SMU) which results in a high mass impact but preliminary increases AIT effort and thereby the overall satellite costs. Sensor bus architectures reduce AIT cost by reduction of wiring effort, reduction in required test time and by providing a flexible sensor network topology.The HSB system is based on a modular concept including a controller module, a fiber-optic interrogator module and an I²C electric interrogator module The HSB system provides advanced performance which includes programmable and sensor specific alarm functions, averaging of dedicated sensor values and thereby a reduction of SMU processor load. The combination of electrical I²C sensors for punctual resolved measurements and fiber-optic sensors for e.g. thermal mapping of panels by embedding sensor fibers in the satellite structures results in a versatile system.In this paper we present the design of the HSB system taking into account the requirements from European platform manufacturers. The HSB design yields a product which can be implemented as replacement of standard p2p systems to build up a more cost efficient sensor system for geostationary satellites. MOTIVATION OF HSB DEVELOPEMENTState-of-the-art telecommunication satellite platforms have to process a tremendous amount of monitoring data to fulfill tasks, as e.g. attitude and orbit control. Especially for temperature monitoring hundreds of sensors are required. They are currently point-to-point wired in a star configuration covering the whole satellite. This results in a complex sensor harness which increases mass, AIT effort and therefore the overall satellite costs. An additional problem arises because of the inflexibility of the state-of-the-art wiring. In the integration phase of the satellite the harness and the panels are the first subsystems to be integrated. All other subsystems are integrated afterwards. If any problem arises during tests concerning the sensor harness (e.g. more sensors required or sensors on wrong position) the harness must be partly extracted from the satellite. This has the consequence, that some of the subunits also have to be extracted. The full procedure, caused by the inflexibility of the wiring, has a high effort and increases the costs dramatically.In Figure 1, part of the GALILEO harness is illustrated. The wires in brown and white color are used for temperature monitoring and control. All p2p-wired temperature sensors are fed to a multiplexing unit, to be queried by the SMU. This results in a high SMU processor load only for monitorin...

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