  With the goal of a space-based quantum network is to have satellites
distribute keys between any nodes on the ground, we consider an evolved quantum
network from a near-term form, in which a space-based relay, satellite executes
a sequence of satellite-based quantum key distribution (SatQKD) missions,
allowing any two ground nodes to have a shared secure key. Accordingly, we
develop a comprehensive framework for the dynamic simulation of SatQKD and
consider scheduling QKD downlink in future space-based quantum communication
network. The embedding of precise orbital model including beam diffractions and
atmosphere effects makes our framework more realistic. Incorporated with the
local meteorological data to channel loss model, the cloud cover contribution
to transmission disturbance is quantified to realize a quasi-experimental
scenario. We provide a trade-off consideration between the duration available
for communications and its corresponding average link loss during one orbit,
which could be used to support decisions involving the locations of ground
stations and the selection of the orbital parameters for a quantum satellite.
Our work also shows that satellite downlink schedule could allow for the
possibility to consider strategies for different SatQKD missions such as
extending connection for distant ground nodes, prioritized delivery, or
promoting keys utilization, which can be used as a guideline to support
decisions for future satellite application.
