Integrated Software and Sensor Health Management for Small Spacecraft

Abstract

Despite their size, small spacecraft have highly complex architectures with many sensors and computer-controlled actuators. At the same time, size, weight, and budget constraints often dictate that small spacecraft are designed as single-string systems, which means that there are no or few redundant systems. Thus, all components, including software, must operate as reliably. Faults, if present, must be detected as early as possible to enable (usually limited) forms of mitigation. Telemetry bandwidth for such spacecraft is usually very limited. Therefore, fault detection and diagnosis must be performed on-board. Further restrictions include low computational power and small memory.In this paper, we discuss the use of Bayesian networks (BNs) to monitor the health of on-board software and sensor systems, and to perform advanced on-board diagnostic reasoning. Advanced compilation techniques are used to obtain a compact SSHM (Software and Sensor Health Management) system with a powerful reasoning engine, which can run in an embedded software environment and is amenable to V&V. We successfully demonstrate our approach using an OSEK-compliant operating system kernel, and discuss in detail several nominal and fault scenarios for a small satellite simulation with a simple bangbang controller.

Software health management with Bayesian networks

“…In addition, several diagnostic messages contradicted each other. 2 If the diagnostics had been system-wide, the number of warnings (and the pilot's workload) could have been reduced tremendously and no contradictory diagnostic messages would have been produced.…”

“…In our approach, we use Bayesian networks to model the nominal and off-nominal behavior of software [2]. Our modelling of software is inspired by previous work on system health management for electrical power systems [9], [10], [11] in which each electrical power system component is represented by a small number of nodes (typically 2-6), and then separate Bayesian networks structures represent the connections between components.…”

“…Further details on this approach to software and sensor monitoring, applied to small satellites and using scenarios with injected faults, are available in [2]. In our demonstration, we have implemented the SWHM concept using Bayesian networks, which model software as well as interfacing hardware sensors.…”

“…Only recently, health management systems that monitor software have been developed (for an overview see, e.g., [1]). In this paper, we will briefly discuss our approach of using Bayesian networks for software health management (SWHM) [2][3][4].…”

“…At the same time, it is important to utilize and extend existing results from more traditional FDDR areas. In our SWHM approach, briefly presented here and discussed in more detail elsewhere [2][3][4], we are using Bayesian networks [13], [14] to define the health model for the software to be monitored. In this extended abstract, we will first discuss SWHM requirements, which make advanced reasoning capabilities for the detection and diagnosis important.…”