  This article develops a protocol to synchronize clocks on board a network of
satellites equipped with quantum resources. We show that, in such a
constellation, satellites reinforce each other's sync capabilities, forming a
common clock that is more stable and precise than its constituents. We envision
the resulting network as a master clock able to distribute time across the
globe, providing the basis for a future quantum global navigation satellite
system or a space-based quantum network. As an example of its capabilities, we
show that a constellation of 50 satellites equipped with modest quantum
resources, and distributed amongst 5 orbits at an altitude of 500 km, allows
the synchronization of clocks spread across the globe at sub-nanosecond
precision.
