Approximation methods for estimating the availability of optical ground networks

Optical communications are a key technology enabler to return increasing amounts of data from space exploration platforms such as robotic spacecraft in Earth orbit or across the solar system. However, several challenges have hindered the deployment and utilization of this technology in an operational context, most notably its sensitivity to atmospheric impairments such as cloud coverage. To mitigate this problem, building a network of interconnected and geographically disperse ground stations has been proposed as a possible solution to ensure that, at any point in time, at least one space-to-ground optical link is available to contact the space-based platforms. In this paper, we present a new approach for quantifying the availability of an optical ground network that is both computationally inexpensive and suitable for high-level architectural concept studies. Based on the cloud fraction data set, several approximation methods are used to estimate the probability of having a certain number of space-to-ground links fail due to cloud coverage. They are developed in order to capture increasingly complex atmospheric factors, from sites with independent weather conditions, to stations that are both temporally and spatially correlated. Then, the proposed approximation methods are benchmarked and recommendations on how to utilize and implement them are finally summarized.