Persistence-based production rules for on-board satellite automation

As the cost of operations comes under greater scrutiny, the use of automated systems is receiving greater attention. A vital aspect of on-board automation is the manner in which system knowledge and operational procedures are represented. Production rules are a commonly-implemented method. They possess the advantage of coherent, logical formulation of responses, represented in a manner consistent with operational procedures. However, they can be inflexible to changing parameters, insensitive to issues of time duration, and require many rules to cover all cases. To be of greater use to automated space missions, production-rule systems need to be augmented with the ability to handle uncertainty and incorporate temporal characteristics. As part of its research program in space system operations and autonomy, Stanford University´s Space Systems Development Laboratory (SSDL) has developed an advanced production rule approach to automation. These production rules track the temporal persistence of conditionals as a primitive aspect of their implementation. The persistence-based production rules have been integrated into the Chatterbox flight software on Sapphire, SSDL´s first satellite. Chatterbox´s programmable production rules control a beacon-based health management system as well, as other on-board activities. This paper motivates the use of persistence as an integral aspect of automated health monitoring, introduces the concept of an “integral of threat” to replace static alarm thresholds, describes how persistence tracking has been integrated into Chatterbox, and reviews the applications of the resulting system for SSDL´s spacecraft