Evaluation of Fault Tolerant Online Scheduling Algorithms for CubeSats

Small satellites, such as CubeSats, have to respect time, spatial and energy constraints in the harsh space environment. To tackle this issue, this paper presents and evaluates two fault tolerant online scheduling algorithms: the algorithm scheduling all tasks as aperiodic (called ONEOFF) and the algorithm placing arriving tasks as aperiodic or periodic tasks (called ONEOFF & CYCLIC). Based on several scenarios, the results show that the performances of ordering policies are influenced by the system load and the proportions of simple and double tasks to all tasks to be executed. The “Earliest Deadline” and “Earliest Arrival Time” ordering policies for ONEOFF or the “Minimum Slack” ordering policy for ONEOFF & CYCLIC reject the least tasks in all tested scenarios. The paper also deals with the analysis of scheduling time to evaluate real-time performances of ordering policies and shows that ONEOFF requires less time to find a new schedule than ONEOFF & CYCLIC. Finally, it was found that the studied algorithms perform well also in a harsh environment.