Next generation of Guidance Navigation Satellite Systems will require an increase in the available power of navigation signals at the receiver on ground. Current FOC Galileo satellites under development make use of TWTAs to provide an output power of nearly 200W (E1 band). Next generation of Galileo satellites will require higher output powers (2dB more) what implies a challenge in the design and implementation of the high power amplifier unit. Obtaining the required output power levels with certain efficiency and within preset linearity requirements is a key requirement for the optimisation of the payload, which can be satisfied with GaN technology. At L-band efficiency of GaN SSPA in spacecraft is similar to efficiency of TWTAs and it presents as advantage that GaN SSPA requires 2 times smaller area than TWTAs which leads to a 2.5 times lower weight.There are important efforts in Europe focused on demonstrating the capabilities of GaN technology applied to HPAs. Despite of the promising results, the tests are carried out on breadboards. Thus, for real space application it’s necessary to fill the gap between breadboard and final HPA FM, taking into account all the constrains given by space segment: environmental, mass, consumption,… The aim of SLOGAN project is to evaluate and apply the potentiality of mature UMS European GaN based technology (GH-50) through the realization of a GaN SSPA EQM for the next generation of Galileo satellites. The objective is to make the development for E1 band as it is the most challenging in terms of output power. The development of SLOGAN project will allow not only to show the feasibility of implementing a high output power GaN SSPA for Galileo application, but also will open the door to a wide variety of applications (such as radio broadcasting, Tx/Rx modules for Earth Observation space & airborne radars, etc.) in which GaN technology with its increased power and mass efficiency promises a clear advantage over current solutions.