Development of the active space hydrogen maser for the ACES space experiment of ESA

In the frame of the scientific mission Atomic Clock Ensemble in Space (ACES), Observatoire de Neuchâtel (ON), Switzerland, is developing the Space Hydrogen Maser (SHM) in collaboration with Contraves Space AG (CSAG), Switzerland. The Physics Package of the Engineering Model is assembled and performs as specified: for nominal operational parameters, the long-term frequency stability is 1×10^-15 @ 10´000s, thanks to the Automatic Cavity Tuning (ACT). The ACT concept based on a pulsed interrogation scheme of the cavity has been developed and demonstrated with a laboratory demonstrator at ON. The space compatible electronics package is being assembled by CSAG and preliminary functional tests are satisfactory.