Application of FBG sensors to temperature measurement on board of the REXUS 22 sounding rocket in the framework of the U-PHOS project

U-PHOS (Upgraded PHP Only for Space) is a project developed within the REXUS/BEXUS programme framework, by a team of students from the University of Pisa with the goal to analyse and characterize the behaviour of a Pulsating Heat Pipe (PHP), one of the most attractive two phases passive systems for thermal management in space applications. The PHP consists of a sealed serpentine capillary tube filled with a working fluid. The heat is efficiently transported by means of the combined action of phase change and capillary forces, so no extra equipment is required. The project aims at investigating the thermal response of such a device under a milli-gravity condition, in order to assess its effectiveness in space conditions. To do so, the power delivered to the system, the internal pressure of the PHP and in particular its temperature in several points must be measured. The temperature measurements are performed by an innovative fibre sensing solution based on arrays of fibre Bragg Gratings (FBGs), which act as temperature sensors at specific locations along only one optical fibre. This paper intends to describe the system built by the students, focusing on the FBG temperature measurements systems. A comparison between the adopted solution and other possible measurement systems is performed, highlighting advantages and drawbacks.