Distributed computing on Emerald: a modular approach for robust distributed space systems

A modular, distributed bus architecture potentially offers significant advantages throughout a satellite's lifecycle. Specifically this architecture enables:- During ground integration: incremental integration of subsystems even if crucial parts, such as the CPU, are delayed; using the Internet for "virtual integration" between remote locations. On-orbit: sharing resources within a satellite; no cost redundancy, including directly commanding subsystem through the communication subsystem, should the CPU fail. And when extended to a multi-satellite mission: multiple satellites to be inter-connected as a single "virtual bus"; autonomous reallocation and sharing of resources across satellites, including adapting to subsystem failures; autonomous experiment coordination. This paper explores the benefits and challenges of single and multi-satellite distributed architectures and the unique strategies they enable. The data architecture for the two-satellite Emerald mission is used as an example. Emerald uses an I2C serial bus to connect PICmicro based "smart" subsystems.