  Heterogeneous teams of robots, leveraging a balance between autonomy and
human interaction, bring powerful capabilities to the problem of exploring
dangerous, unstructured subterranean environments. Here we describe the
solution developed by Team CSIRO Data61, consisting of CSIRO, Emesent and
Georgia Tech, during the DARPA Subterranean Challenge. These presented systems
were fielded in the Tunnel Circuit in August 2019, the Urban Circuit in
February 2020, and in our own Cave event, conducted in September 2020. A unique
capability of the fielded team is the homogeneous sensing of the platforms
utilised, which is leveraged to obtain a decentralised multi-agent SLAM
solution on each platform (both ground agents and UAVs) using peer-to-peer
communications. This enabled a shift in focus from constructing a pervasive
communications network to relying on multi-agent autonomy, motivated by
experiences in early circuit events. These experiences also showed the
surprising capability of rugged tracked platforms for challenging terrain,
which in turn led to the heterogeneous team structure based on a BIA5 OzBot
Titan ground robot and an Emesent Hovermap UAV, supplemented by smaller tracked
or legged ground robots. The ground agents use a common CatPack perception
module, which allowed reuse of the perception and autonomy stack across all
ground agents with minimal adaptation.
