  Avalanche photodiodes (APDs) are well-suited for single-photon detection on
quantum communication satellites as they are a mature technology with high
detection efficiency without requiring cryogenic cooling. They are, however,
prone to significantly increased thermal noise caused by in-orbit radiation
damage. Previous work demonstrated that a one-time application of thermal
annealing reduces radiation-damage-induced APD thermal noise. Here we examine
the effect of cyclical proton irradiation and thermal annealing. We use an
accelerated testing environment which emulates a realistic two-year operating
profile of a satellite in low-Earth-orbit. We show that repeated thermal
annealing is effective at maintaining thermal noise of silicon APDs within a
range suitable for quantum key distribution throughout the nominal mission
life, and beyond. We examine two strategies -- annealing at a fixed period of
time, and annealing only when the thermal noise exceeds a pre-defined limit. We
find both strategies exhibit similar thermal noise at end-of-life, with a
slight overall advantage to annealing conditionally. We also observe that
afterpulsing probability of the detector increases with cumulative proton
irradiation. This knowledge helps guide design and tasking decisions for future
space-borne quantum communication applications.
