Performance demonstration of the on-board active hydrogen maser for the ACES space mission of ESA

In view of the ESA scientific space mission "Atomic Clock Ensemble in Space" (ACES), aimed in particular at verifying fundamental general relativity laws, state-of-the-art atomic clocks are required. In order to overpass the medium term performance of the on-board primary cold Cesium beam frequency standard (PHARAO), a Space active Hydrogen Maser (SHM) is mandatory. Observatoire de Neuchâtel, Switzerland (ON) is currently developing this maser, focusing on the atomic resonator, while its partner Oerlikon Space AG (OSAG) is developing the control and frequency locking electronics.