PHOS Project (www.phosproject.com) was launched on March 18th, 2015, from the Esrange Space Center (SSC) in Kiruna, Sweden. The aim of the project was to test two Closed Loop Pulsating Heat Pipes (CLPHPs) in 90 seconds microgravity experienced on board REXUS18 sounding rocket. The REXUS/BEXUS programme is realised under a bilateral Agency Agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB). The programme offers a unique opportunity for students to get in touch with research activities and engineering challenges related to the space field. Despite PHOS Project short duration (20 Months) with respect to real space projects of larger scale, several challenges was encountered related both to the technical implementation (design, development, manufacturing and testing) of the experimental system to be interfaced to the rocket and to the programmatic and organizational aspects (management, team working, cost analysis, industrial cooperation). In the present paper, the design of the experimental set-up and the experimental results are briefly discussed, even though it was not possible to experience the expected low gravity conditions due to a failure of the rocket's yo-yo de-spin system. Moreover, all the lesson learned related to the project development are properly recognized and listed, highlighting efforts and learning curve of the junior team members to respect mandatory deadlines and reviews. With these reported lessons learned, this paper could be a basis for future Student teams that intend to participate a stimulating programme like REXUS/BEXUS. The implementation issues encountered and the trade-offs analysis, which has been made between different design solutions in order to meet mission requirements, are reported. Finally storage constraints and a refurbishment strategy for possible future re-flight are described.