Using Rescheduling and Flexible Execution to Address Uncertainty in Execution Duration for a Planetary Rover

During execution, activity durations may vary from those predicted in the generated schedule. In this article we study (re) scheduling invocation, execution during rescheduling, and flexible execution to enable a high level of responsiveness to uncertainty in activity execution duration. We discuss these methods theoretically in the context of an embedded scheduler and practically in the context of a limited CPU embedded scheduler with a nonzero scheduler runtime intended for a planetary rover. We use the concept of a commit window to enable execution of the previously generated schedule while (re) scheduling. We define \textit{Fixed Cadence} and \textit{Event Driven} scheduling as methods to decide when to reinvoke the scheduler. We define and analyze \textit{Flexible Execution (FE)} as an approach to execute the generated schedule while adapting it to variations in execution. Specifically, FE focuses on (1) how to take advantage of activities ending earlier than expected and (2) how to maintain a consistent schedule if activities take more time than expected. We present a theoretical model and empirical results documenting how these various methods interact and perform on both synthetic data and best available data for NASA's next planetary rover, the Mars 2020 rover. We then describe how these analyses influenced the onboard software for the Mars 2020 rover.