Abstract: Optical communications system (10) and method for transmission of payload data (PD) from a low earth orbit satellite (20) to an optical ground terminal (30), the low earth orbit satellite (20) being connectable with the optical ground terminal (30) via an optical downlink channel (DL), and the optical ground terminal (30) being connectable with the low earth orbit satellite (20) via an uplink channel (UC); wherein said uplink channel (UC) is an acquisition and tracking beacon channel by means of a ground beacon (GB) controlled by a point-acquisition-track subsystem (PAT), the ground beacon (GB) comprising a wide angle beam (W) for acquisition and a guidance beam (G) for tracking; and wherein the ground beacon (GB) for the uplink channel (UC) is a pulse position modulated PPM channel.

Abstract: Optical downlink system (10) and method of optical data transmission between a remote terminal (20) having a number of n optical communication terminals (OT1-OTn), and a ground terminal (30) comprising a cluster of n optical ground stations (OGS1-OGSn) connected by n optical downlink channels (DL1-DLn) respectively n optical uplink channels (UC1-UCn) characterised by a spatial separation of the optical downlink channels (DL1-DLn) and a temporal separation of the optical uplink channels (UC1-UCn).