Introduction to the Sirio-2 program

The Sirio-2 meteorological data distribution (MDD) and laser synchronization from stationary orbit (LASSO) projects are described. The MDD mission provides links between small ground stations for meteorological data within the global telecommunications network of the World Meteorological Organization in Africa. Twenty-four 100 bps channels PCM/PM, and twelve 2400 bps channels PCM/PSK/PM are used. The MDD system elements are: small ground stations (40 dBW EIRP); transponder; and mechanically despun antenna on the satellite. The LASSO mission ensures intercontinental time comparison employing laser techniques, with accuracy of 1 nsec or better. It gives high availability to users and relatively free access to the system. The LASSO experiment consists of synchronizing two atomic clocks, linked to the ground laser station, to a very high precision by: on-board reception of lase pulses coming from the Earth; time tagging of the incoming light pulses; reflecting part of the pulses to the ground laser stations; and data handling and computation.