One of the most persistent urban legends was that of alligators living in New York’s sewer system. To this day, city dwellers look at manholes and wonder what lurks below. On a more scientific level, the DARPA Subterranean Challenge is encouraging the development of commercial robotics and drones to help explore underground complexes.

The U.S. Defense Advanced Research Projects Agency, or DARPA, launched its Subterranean Challenge in 2017. “SubT’s” goal is to advance the development of systems to enhance “situational awareness capabilities” for underground missions. While this may conjure images of military machines patrolling underground like in The Matrix, in reality, one of Earth’s last frontiers lies below its surface.

As the DARPA Subterranean Challenge moves closer to its finale in 2021, the agency is beginning the first phase of three planned real-world tests. According to the contest description, the initial focus area will be “human-made tunnel systems,” followed by “underground urban environments such as mass transit and municipal infrastructure,” and then concluding with “naturally occurring cave networks.”

Subsurface summer delving

This summer, DARPA issued a request for information for subsurface infrastructure in the interest of “global security and disaster-related search-and-rescue missions.”

Teams of technologists are competing for $2 million for hardware inventions and $750,000 for software innovations that “disruptively and positively impact how the underground domain is leveraged,” according to DARPA. The systems under development include platforms “to rapidly map, navigate, and search unknown complex subterranean environments to locate objects of interest.”

“One of the main limitations facing warfighters and emergency responders in subterranean environments is a lack of situational awareness; we often don’t know what lies beneath,” explained Timonthy Chung, DARPA program manager.

“We’ve reached a crucial point where advances in robotics, autonomy, and even biological systems could permit us to explore and exploit underground environments that are too dangerous for humans,” added Fred Kennedy, director of DARPA’s Tactical Technology Office. “Instead of avoiding caves and tunnels, we can use surrogates to map and assess their suitability for use.” He even coined a catchphrase for the challenge: “Making the inaccessible accessible.”

In an abandoned Pennsylvania coal mine on a sweltering August afternoon, 11 teams from across the globe came with 64 terrestrial robots, 20 unmanned aerial vehicles, and one autonomous blimp to compete. The first course in the Subterranean Challenge included four events, each lasting an hour. Each team’s fleet of machines had to autonomously locate, identify and record 20 items or artifacts deep inside the mine, which was originally built by the Pittsburgh Coal Company in 1910.

CMU team pulls ahead in Subterranean Challenge

The only team to score in double digits in all four independent runs was Explorer of Carnegie Mellon University (CMU).

CMU is a DARPA Challenge favorite, with a winning record that includes the 2007 Urban Challenge and the 2015 Robotics Challenge. This year, it had the distinct advantage of being local, scouting out the location beforehand to better plan its tactics for live competition.

“Explorer regularly practiced at the Tour-Ed Mine in Tarentum, which is normally only frequented by tourists who want to check out a coal mine formerly owned by Allegheny Steel,” wrote Courtney Linder of Popular Mechanics. “They periodically flew drones and watched their ground robots exploring the cavernous, maze-like depths.”

One of the biggest hurdles for teams in the Subterranean Challenge is the lack of Global Positioning System (GPS) signals and Wi-Fi communications. To safely navigate the cavernous course of these GPS-denied environments, SubT machines had to rely solely on a fusion of onboard sensors, including lidar, cameras, and radar.

Sebastian Scherer, lead of the CMU team, explained to the the Pittsburgh Post-Gazette that his team employed up to eight robots to create its own Wi-Fi network to “talk” to one another while simultaneously mapping the environment. Deploying a swarm approach, the robots acted as a collective unit working together to fill in data gaps, which meant that even if one went offline, it was still able to pilot using its onboard systems and previously downloaded maps.

Leading up to the competition, the CMU team usd computer simulations to strategize its approach, but it understood the limitations of exclusively planning in the virtual world. As Scherer’s collaborator, Matt Travers, explained, “Our system may work perfectly in simulation, and the first time we deploy, we may take the exact same software from the simulation and put it in the robot, and it drives right into a wall, and you go figure out why.”

Seeking environment-agnostic solutions

While Explorer walked off with some nominal prize money, all 11 teams are committed to the same goal of full autonomy, regardless of the environment and manual input.

“We’d like to build a system that’s going to be agnostic to the types of mobility challenges that we’ll face,” said Travers. “And this is certainly a difficult thing to do.”

The August round of the DARPA Subterranean Challenge showed how creativity can be harnessed and the global robotics community can unify to help save lives.

“We are inspired by the need to conduct search-and-rescue missions in a variety of underground environments, whether in response to an incident in a highly populated area, a natural disaster, or for mine rescue,” said Chung.

The next round will take place in February, quite possibly in the sewers of New York City (alligators and all). Chung cautioned the contestants: “Prepare for a few new surprises. The SubT Challenge could be compared to a triathlon. DARPA is not looking just for the strongest swimmer, runner, or cyclist, but rather integrated solutions that can do all three.”

The Robot Report is launching the Healthcare Robotics Engineering Forum, which will be on Dec. 9-10 in Santa Clara, Calif. The conference and expo will focus on improving the design, development, and manufacture of next-generation healthcare robots. Learn more about the Healthcare Robotics Engineering Forum, and registration is now open.

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