  In this work, we explore the feasibility of performing satellite-to-Earth
quantum key distribution (QKD) using the orbital angular momentum (OAM) of
light. Due to the fragility of OAM states the conventional wisdom is that
turbulence would render OAM-QKD non-viable in a satellite-to-Earth channel.
However, based on detailed phase screen simulations of the anticipated
atmospheric turbulence we find that OAM-QKD is viable in some system
configurations, especially if quantum channel information is utilized in the
processing of post-selected states. More specifically, using classically
entangled light as a probe of the quantum channel, and reasonably-sized
transmitter-receiver apertures, we find that non-zero QKD rates are achievable
on sea-level ground stations. Without using classical light probes, OAM-QKD is
relegated to high-altitude ground stations with large receiver apertures. Our
work represents the first quantitative assessment of the performance of OAM-QKD
from satellites, showing under what circumstances the much-touted higher
dimensionality of OAM can be utilized in the context of secure communications.
