Spacecraft and instrument Level-0 command and data handling subsystem

A Level-0 processor is a low-level command processor intended to control the spacecraft whenever the main processor is off-line. Such an event can happen during early orbit activities, during load shedding operations or during an anomaly (like the upset of the main processor due to cosmic radiation). During these periods, the safe mode processor collects a subset of normal housekeeping telemetry, formats it, and downlinks it along with the command link control word information required by the CCSDS Telecommand recommendations. This subset of normal telemetry collection includes housekeeping telemetry from critical spacecraft subsystems such as attitude control, power regulation, solar array control, and payload maintenance. To determine the optimal number of interfaces and telemetry points, SwRI polled several spacecraft vendors and used this information to implement Level-0 CCSDS command processing/telemetry collection. This paper presents Southwest Research Institute's continuing development of flexible Level-0 command and telemetry collection hardware.