In 2000s era, aircraft propulsion systems are achieving an outstanding level of e??fficiency. Design optimization further increases components’ performance, while lean combustion processes tend to reduce CO2 and NOx emissions. However, pollution reduction targets, especially those imposed for the next 30 years, are extremely strict and demanding, so much that conventional architectures, based on the thermodynamic Brayton cycle, can not fulfil them. Because of this main reason, alternative energies has to be taken into account, and precisely the electric one is going to be the leader. Coupling a gas-turbine engine within an electric propulsion system is one of the main challenges which aeronautical industries are facing to, but it is also one of the principal ways forward in order to meet emissions goals.