  Photon loss is the fundamental issue towards the development of quantum
communication. We present a proposal to mitigate photon loss even at large
distances and hence to create a global-scale quantum communication
architecture. In this proposal, photons are sent directly through space, using
a chain of co-moving low-earth orbit satellites. This satellite chain would
bend the photons to move along the earth's curvature and control photon loss
due to diffraction by effectively behaving like a set of lenses on an optical
table. Numerical modeling of photon propagation through these "satellite
lenses" shows that diffraction loss in entanglement distribution can be almost
eliminated even at global distances of 20,000 km while considering beam
truncation at each satellite and the effect of different errors. In the absence
of diffraction loss, the effect of other losses (especially reflection loss)
becomes important and they are investigated in detail. The total loss is
estimated to be less than 30 dB at 20,000 km if other losses are constrained to
2% at each satellite, with 120 km satellite separation and 60 cm diameter
satellite telescopes eliminating diffraction loss. Such low-loss
satellite-based optical-relay protocol would enable robust, multi-mode global
quantum communication and wouldn't require either quantum memories or repeater
protocol. The protocol can also be the least lossy in almost all distance
ranges available (200 - 20,000 km). Recent advances in space technologies may
soon enable affordable launch facilities for such a satellite-relay network. We
further introduce the "qubit transmission" protocol which has a plethora of
advantages with both the photon source and the detector remaining on the
ground. A specific lens setup was designed for the "qubit transmission"
protocol which performed well in simulation that included atmospheric
turbulence in the satellite uplink.
