SUMMARYThe Fiber Sensor Demonstrator (FSD), for ESA's Proba-2 satellite is the first demonstration of a full fiber-optic sensor network in the space environment on a satellite. MPB Communications (MPBC) has developed the FSD as a lightweight (<1.3 kg) fiber-optic sensing system. It was launched on Proba-2 in November 2009 and is still completely functional, almost seven years after its launching. FSD contains also the first fiber laser in space, it is used to sweep the spectral range and read the intensity at each wavelength between 1520 and 1560 nm. The optoelectronic components and data acquisition board are about 500 g, and the rest (<800 g) is the mass of the protective monolithic aluminium enclosure that has to resist to the launching mechanical shock and vibrations.The advantages of the FSD approach include a central interrogation module that is positioned remotely from the sensors and used to control a variety of different fiber-optic sensors, based on Fiber Bragg Gratings (FBG).The FSD contains six parallel fiber lines multiplexed within the interrogation module. Sixteen speciallypackaged FBG temperature sensors are distributed on four fiber lines. They monitor the temperature at different locations in the propulsion system and the spacecraft bus over the range of -60 °C and +120°C. The fifth fiber line is dedicated to a High-Temperature (HT) sensor to measure the transient temperature response of the SSTL thruster to beyond 350°C. The last fiber line contains an innovative Pressure/Temperature (P/T) sensor that provides both temperature and pressure measurements of the SSTL Xe propellant tank.The fiber sensors are monitored periodically over the seven years of flight. Their measurements fit well with the standard sensors used by the satellite. The evolution of the FSD response in space shows the fibers and Interrogation module parameters are within 10 % variations, including the laser diodes power and the FBG sensors intensity. The total gamma radiation received by the FSD is about 7 krad, during the 7 years.