Development of a Monitoring and Switchover System for Redundant Computers in a Fault-Tolerant Navigation System for Space Transportation Applications

Abstract

The reliability of electronic systems is a significant challenge in the development of new devices.In particular, for a critical system in the aerospace area, it is essential to provide safety andreliability. To use redundancy in critical systems is a common method to increase reliability. Tripleredundancies are typically used in aircraft. This method can recognize a faulty system by a majoritydecision. The Hybrid Navigation System (HNS) of the Reusability Flight Experiment (ReFEx) alsouses redundancy to improve the reliability of the system. These critical components are available atleast twice to compensate a failure. In the case of the Onboard Computer (OBC) used in the HNS,the redundancy concept creates a problem to detect an error. Also, the distribution of the sensorsignals is not possible without further ado. This thesis shows the development of a system that cansolve these problems. The systems provide observing functions like a challenge-response protocol,a comparison of the navigation solution and a syntactical check of the navigation solution. Thesefunctions are included in the Sentinel part of the prototype. A microcontroller for the Sentinelwas used as the logic module. In this microcontroller, a Real Time Operating System (RTOS) wasimplemented to support real-time features. All observing functions are implemented in this RTOS.In addition, an signal distribution unit endorses the distribution of outgoing and incoming signalsand can switch the outgoing signals in case of a failed OBC system. To support a fast and reliableprocess, a Complex Programmable Logic Device (CPLD) was used for this task. The variousdevelopment steps are covered, from reading the requirements to the concept to the hardware andsoftware design. It must be taken into account that the development shown, corresponds to aprototype that does not yet have the full scope of the later flight model. The developed prototypeshows the primary function of observation and signals transmission for the OBCs. Finally, thework shows the verification process of the prototype