Optical satellite communications play an increasingly important role in a number of space applications. However, if the system concept includes optical links to the surface of Earth, the limited availability due to clouds and other atmospheric impacts need to be considered to give a reliable estimate of the system performance. An OGS network is required for increasing the availability to acceptable figures.

In order to realistically estimate the performance and achievable throughput in various scenarios, this activity developed a simulation tool under ESA contract. The tool is based on a database of five years of cloud data with global coverage and can thus easily simulate different optical ground station network topologies for LEO- and GEO-to-ground links. Further parameters, for example limited availability due to sun blinding and atmospheric turbulence, were also considered. Several scenarios were investigated: LEO-to-ground links, GEO feeder links, and GEO relay links. The key results of the optical ground station network optimisation and throughput estimations are presented. The implications of key technical parameters, for example memory size aboard the satellite, are discussed. Finally, potential system designs for LEO- and GEO-systems are presented.