Clock monitoring and control units for navigation satellites

All signal generation and transmission frequencies in the payload of a navigation satellite are typically derived from a single 10.23 MHz master clock. In case of the current payload architecture of the Galileo or other Navigation System this Master Timing Reference (MTR) is synthesized in a Clock Monitoring and Control Unit (CMCU) based on one single atomic reference. To achieve this, in the current Galileo design the CMCU selects the active clock from a pool of two Rubidium Atomic Frequency Standards (RAFS) and two Passive H-Masers (PHM) and synthesizes the MTR from this source. A second atomic clock is kept in hot redundancy and monitored inside the CMCU for its phase drift against the active clock.