Temporal brittleness analysis of task networks for planetary rovers

Abstract

We propose a new method to analyze the temporal brittleness of task networks, which allows the detection and enumeration of activities that, with modest task execution duration variation make the execution of the task network dynamically uncontrollable. In this method, we introduce a metric for measuring an activity brittleness - defined as the degree of acceptable deviation of its nominal duration - and describe how that measurement is mapped to task network structure. Complementary to existing work on plan robustness analysis which informs how likely a task network is to succeed or not, the proposed analysis and metric go deeper to pinpoint the sources of potential brittleness due to temporal constraints and to focus either human designers and/or automated task network generators (e.g. scheduler/planners) to address sources of undesirable brittleness. We apply the approach to a set of task networks (called sol types) in development for NASA's next planetary rover and present common patterns that are sources of brittleness. These techniques are currently under evaluation for potential use supporting operations of the Mars 2020 rover.