Anomaly detection using the emerald nanosatellite on board expert system

An expert system is a type of program designed to model human knowledge and expertise. This work describes the design, implementation, and testing of an onboard expert system developed for the dual spacecraft Emerald small satellite mission. This system takes advantage of Emerald's distributed computing architecture and is currently being used for on-board fault detection. The distributed computing architecture is composed of a network of PICmicro and Atmel microcontrollers linked together by an I/sup 2/C serial data communication bus which also supports sensor and component integration via Dallas 1-wire and RS232 standards. The expert system software is executed by an Atmel microcontroller within Emerald's expert subsystem hardware. The human knowledge and expertise that the system simulates is contained within software "rules" that can be easily modified from the ground. The flexibility offered by this system allows the ground operator to add, modify, or remove logical operations on-orbit and overcomes the limitations imposed by hardwired systems. While expert systems have been used on spacecraft in the past, its role on Emerald for on-board fault-detection using threat integrals and persistence counters further demonstrates the power and versatility of such systems. Results include experimental data verifying the expert system's performance and its ability to distinguish threat levels posed by out-of-limit sensor readings. This paper describes the technical design of the aforementioned features and its use as part of the Emerald satellite mission.