This paper presents and discusses algorithms, hardware, and software architecture developed by the TEAM CoSTAR (Collaborative SubTerranean Autonomous Robots), competing in the DARPA Subterranean Challenge. Specifically, it presents the techniques utilized within the Tunnel (2019) and Urban (2020) competitions, where CoSTAR achieved 2nd and 1st place, respectively. We also discuss CoSTAR's demonstrations in Martian-analog surface and subsurface (lava tubes) exploration. The paper introduces our autonomy solution, referred to as NeBula (Networked Belief-aware Perceptual Autonomy). NeBula is an uncertainty-aware framework that aims at enabling resilient and modular autonomy solutions by performing reasoning and decision making in the belief space (space of probability distributions over the robot and world states). We discuss various components of the NeBula framework, including: (i) geometric and semantic environment mapping; (ii) a multi-modal positioning system; (iii) traversability analysis and local planning; (iv) global motion planning and exploration behavior; (i) risk-aware mission planning; (vi) networking and decentralized reasoning; and (vii) learning-enabled adaptation. We discuss the performance of NeBula on several robot types (e.g. wheeled, legged, flying), in various environments. We discuss the specific results and lessons learned from fielding this solution in the challenging courses of the DARPA Subterranean Challenge competition.

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Robot swarms herald the ability to solve complex tasks using a large collection of simple devices. However, engineering a robotic swarm is far from trivial, with a major hurdle being the definition of the control laws leading to the desired globally coordinated behavior. Communication is a key element for coordination and it is considered one of the current most important challenges for swarm robotics. In this paper, we study the problem of maintaining robust swarm connectivity while performing a coverage task based on the Voronoi tessellation of an area of interest. We implement our methodology in a team of eight Khepera IV robots. With the assumptions that robots have a limited sensing and communication range-and cannot rely on centralized processing-we propose a tri-objective control law that outperforms other simpler strategies (e.g. a potentialbased coverage) in terms of network connectivity, robustness to failure, and area coverage.

Since the beginning of space exploration, Mars and the Moon have been explored with orbiters, landers, and rovers. Over forty missions have targeted Mars, and more than a hundred, the Moon. Developing novel strategies and technologies for exploring celestial bodies continues to be a focus of space agencies. Multi-robot systems are particularly promising for planetary exploration, as they are more robust to individual failure and have the potential to explore larger areas; however, there are limits to how many robots an operator can individually control. We recently took part in the European Space Agency's interdisciplinary equipment test campaign (PANGAEA-X) at a Lunar/Mars analogue site in Lanzarote, Spain. We used a heterogeneous fleet of Unmanned Aerial Vehicles (UAVs)-a swarm-to study the interplay of systems operations and human factors. Human operators directed the swarm via ad-hoc networks and data sharing protocols to explore unknown areas under two control modes: one in which the operator instructed each robot separately; and the other in which the operator provided general guidance to the swarm, which self-organized via a combination of distributed decision-making, and consensus building. We assessed cognitive load via pupillometry for each condition, and perceived task demand and intuitiveness via self-report. Our results show that implementing higher autonomy with swarm intelligence can reduce workload, freeing the operator for other tasks such as overseeing strategy, and communication. Future work will further leverage advances in swarm intelligence for exploration missions.