Recently, large-scale quantum networks that connect metropolitan area quantum networks between cities have been realized by integrating free-space and fibre quantum key distribution (QKD) links, yet the fibre-based trusted nodes in such networks could be subject to constant surveillance and probes. To remove these fibre-channel risks, we consider a network in which a space-based relay, the Micius satellite, executes a sequence of key delivery missions, allowing any two cities to have a shared key. In this work, we develop a comprehensive framework integrated with precise orbital modelling and a cloud statistics model to enable a preassessment of satellite-based QKD applications. Using this framework, we consider three different scheduling strategies and estimate the keys that can be delivered to cities. The results show that the strategy of pursing the maximum number of final keys significantly embodies space-based QKD advantages, while the strategy of considering different levels of missions achieves the delivery of more keys to higher-priority missions. Most importantly, the targeted strategy of pursuing a distribution of final keys delivered that is coincident with the network traffic distribution guarantees individual needs, further promoting the utilization of the delivered keys in practice. We also provide a comparison of the total number of keys delivered by satellites with different-altitude orbits. It is demonstrated that the plan for constructing a low-Earth orbit (LEO) satellite constellation is more efficient than that for employing an expensive high-orbit satellite in terms of achieving potential applications. Our work not only provides a practical method in the near term but also gives the initial exploration to establish the quantum network.
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