  This article presents the CERBERUS robotic system-of-systems, which won the
DARPA Subterranean Challenge Final Event in 2021. The Subterranean Challenge
was organized by DARPA with the vision to facilitate the novel technologies
necessary to reliably explore diverse underground environments despite the
grueling challenges they present for robotic autonomy. Due to their geometric
complexity, degraded perceptual conditions combined with lack of GPS support,
austere navigation conditions, and denied communications, subterranean settings
render autonomous operations particularly demanding. In response to this
challenge, we developed the CERBERUS system which exploits the synergy of
legged and flying robots, coupled with robust control especially for overcoming
perilous terrain, multi-modal and multi-robot perception for localization and
mapping in conditions of sensor degradation, and resilient autonomy through
unified exploration path planning and local motion planning that reflects
robot-specific limitations. Based on its ability to explore diverse underground
environments and its high-level command and control by a single human
supervisor, CERBERUS demonstrated efficient exploration, reliable detection of
objects of interest, and accurate mapping. In this article, we report results
from both the preliminary runs and the final Prize Round of the DARPA
Subterranean Challenge, and discuss highlights and challenges faced, alongside
lessons learned for the benefit of the community.
