While most interest in constellations of satellites in low Earth orbit has been for systems providing global mobile or fixed broadband communication services, there is also a role for small, inexpensive systems providing specialized services. At the smallest level this is represented by a single microsatellite offering a "store and forward" or messaging service for users who require regular low to medium volume data transfers. We describe the major characteristics of a typical store-and-forward system and outline some of the technological challenges that designers face. We provide a justification for using on-board buffering and focus on the selection of an appropriate channel multiple access scheme that offers certain advantages over conventional Aloha random access.
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