The CMCU from Airbus is a Space Qualified Atomic Clock with two frequency synthesizers that can select independently between two input 9.99-10.01 MHz frequency references. This unit has an output frequency range of 10.23 MHz and short-term residual frequency stability of 6.4 x10-14 (10 s). It has a setting range of ± 1 x 10-8 and a phase meter resolution of 3 ps. The clock generation unit has a phase noise of up to -154 dBc/Hz (100 kHz) and a spurious of -80 dBc. It has a 4 x 2 switch matrix with high isolation to prevent degradation of clock stability and a phase meter to monitor hot redundant against active clock. The clock unit supports MIL-STD-1553B or RS-422 interface for control and monitoring. It requires a power bus voltage of 26-48.5 V and has a power consumption of 21 W. The clock unit has a mass of 5.2 Kg and measures 270 x 216 x 137 mm. Its main application fields include navigation payloads (global or regional), high-performance communication systems, scientific applications, and GNSS overlay systems.