Fault-Tolerant Online Scheduling Algorithms for CubeSats

CubeSats are small satellites operating in harsh space environment. In order to ensure correct functionality on board despite faults, fault tolerant techniques taking into account spatial, time and energy constraints should be considered. This paper presents a software-level solution taking advantage of several processors available on board. Two online scheduling algorithms are introduced and evaluated. The results show their performances and the tradeoff between the rejection rate and energy consumption. Last but not least, it is stated that ordering policies achieving low rejection rate when using the algorithm scheduling all tasks as aperiodic are the "Earliest Deadline" and "Earliest Arrival Time". As for the algorithm treating arriving tasks as aperiodic or periodic tasks, the "Minimum Slack" ordering policy provides reasonable results.