Three different sensors for hydrogen detection have been built and tested within a research project for the European Space Agency. One type is a FBG coated with a palladium layer, detecting the hydrogen by metal hindrance, the strains transmitted to the grating by shear. It works only as a detector and can not quantify the H2 percentage in a gas mixture. A main drawback, common with all palladium based sensors, was a strong temperature dependence, which makes its response time too large at low temperatures. The other two types were intensity based sensors; one of them was a micromirror, with a palladium thin layer at the cleaved end, detecting changes in the backreflected light. The other one as a tapered fibre coated also with palladium; hydrogen will change the refractive index of the palladium, and consequently the amount of losses in the evanescent wave.
A trade-off analysis of sensor performances was done, comparing reproducibility, repetitiveness, robustness, multiplexability, response time and cost. FBG sensor was found to be the most reliable sensor among the optical fibres sensors considered, and the preferred one for space applications.