Exploiting potentials of satellite applications for establishing a global quantum communication network without fibre-based relays

Recent the large-scale quantum network that connects metropolitan area quantum networks between the cities is realized by integrating the free-space and fibre QKD links, yet the fiber-based trusted nodes in such network could be subject to constant surveillance and probes. To remove these fiber-channel risks, we consider a network where a space-based relay, Micius satellite, executes a sequence of keys delivery missions, allowing thus any two cities to have a shared key. In this work, we develop a comprehensive framework integrated with the precise orbital modeling and the cloud statistics model to enable a pre-assessment on the satellite-based QKD applications. Using this framework, we consider three different scheduling strategies and estimate the keys possible to deliver to the cities, respectively. Results show that the strategy of pursing the total final keys maximized significantly embodies space-based QKD advantage, while the strategy of considering different levels of missions achieves more keys delivered to a higher priority mission. Most importantly, the targeted strategy of pursuing the distribution of final keys delivered being coincident with network traffic distribution, guarantees the individual needs, further promoting the utilization of delivered keys in practice. We also provide a comparison between the total number of delivered keys by the satellite with different altitude orbits. It is demonstrated that the plans for constructing a low earth orbit (LEO) satellite constellation, are more effective than that for employing an expensive high-orbit satellite, for a realization of the potential applications. Our works not only provides a practical method in the near term but also gives the aforehand exploration to establish satellite-based quantum communication network.