A robust fault protection architecture for low-cost nanosatellites

There is an increasing trend among many Government and commercial customers towards the use of proliferated small, low-cost satellites to replace large, expensive satellites for near-Earth applications. These small satellites are typically single-string designs that make extensive use of low-cost, commercial-grade components. Consequently, these small, low-cost satellites tend to suffer from inherent low reliability, and even relatively minor on-orbit anomalies can result in catastrophic loss of the mission. Because of the small form factors of many of these satellites, it is difficult to achieve system robustness simply by adding redundant components. In addition, the severe cost constraints imposed on these systems also precludes the use of more traditional high-reliability components. One solution to this problem is to employ a comprehensive, multi-level fault protection system that enables graceful degradation in the event of on-orbit anomalies, and that ensures that the satellite is always thermally safe, power positive, and communicative in all system modes. The fault protection system should also be capable of accommodating the multiple embedded processors that are typically found on modern small satellites. This paper will present the fault protection architecture that Sierra Nevada Corp. is currently developing for a nanosatellite demonstration program. The nanosatellite is a 14 kg space vehicle that uses a 10" optical telescope to perform Earth imaging from 350 km altitude. This spacecraft bus makes extensive use of low-cost cubesat-class components and commercial grade parts. This paper presents an overview of the nanosatellite fault protection and flight software architecture, and discusses how this architecture results in a much more robust and reliable space vehicle.