House hunting on Mars could soon be a thing, and researchers at the University of Arizona are already busy identifying properties that future astronauts could use as habitats. Researchers at the UArizona College of Engineering have developed technology that would allow a herd of robots to explore underground environments on other worlds.
“Lava tubes and caves would be perfect habitats for astronauts because you don’t need to build a structure; you’re protected from harmful cosmic radiation, so all you need to do is make it beautiful and comfortable,” said Wolfgang Fink, partner. professor of Electrical and Computer Engineering at UArizona.
Fink is the lead author of a new paper in the Advances in Space Research which details a communications network that would connect rovers, lakers and even underwater vehicles through a so-called mesh topology network, allowing the machines to work together as a team, independent of human assistance. According to Fink and his colleagues, the approach could help address one of NASA’s Space Technology Grand Challenges by helping to overcome the limited ability of current technology to safely traverse environments on comets, asteroids, moons and planetary bodies . In a nod to the “Hansel and Gretel” fairy tale, the researchers named the patent-pending idea an example of a “Breadcrumb-style Dynamically Growing Communication Network,” or DDCN.
A fairy tale inspires the future
“If you remember the book, you know how Hansel and Gretel threw in breadcrumbs to make sure they found their way back,” said Fink, founder and director of the Optical and Autonomous Exploration Systems Research Laboratory at Caltech and UArizona. “In our scenario, the ‘crumbs’ are tiny sensors that return to the rovers, which deploy the sensors as they traverse a cave or other subterranean environment.”
Constantly monitoring their surroundings and maintaining an awareness of where they are in space, the rovers move on their own, connecting to each other via wireless data links, deploying communication hubs along the way. Once a rover senses that the signal is fading but is still in range, it drops a communication node, regardless of how much distance it has actually traveled since it placed the last node.
“One of the new aspects is what we call opportunistic deployment — the idea that you deploy the ‘crumbs’ when you need to, rather than on a pre-planned schedule,” Fink said.
Meanwhile, there is no need for information from the parent rover. Each subordinate rover will make that determination on its own, Fink added. The system can work in one of two ways, Fink explained. In one, the parent rover acts as a passive receiver, collecting data transmitted by the exploring rovers. In the other, the mother rover acts as an orchestrator, controlling the movements of the rovers like a puppet show.
The machines are taking over
The new concept is coupled with the scalable recognition model devised by Fink and his colleagues in the early 2000s. This concept envisions a group of robots operating at different levels of command — for example, an orbiter controlling a blimp, which in turn controls one or more landers or rovers on the ground. Already, space missions have embraced this idea, several involving UArizona researchers. For example, on Mars, the Perseverance rover commands Ingenuity, a robotic helicopter. An idea for another mission, which was ultimately not selected for funding, proposed sending an orbiter carrying a balloon and a lake lander to study one of the hydrocarbon seas on Saturn’s moon Titan. The breadcrumb approach takes the idea a step further by providing a robust platform that allows robotic explorers to operate underground or even submerged in wet environments. Such swarms of individual, autonomous robots could also help with search and rescue efforts in the wake of natural disasters on Earth, Fink said.
Fink said the biggest challenge, aside from getting the rovers into the underground environment, is retrieving the data they record underground and bringing it back to the surface. The DDCN concept allows a group of rovers to navigate even complex underground environments without ever losing contact with their “mother rover” on the surface. Equipped with a light detection and ranging system, or lidar, they could even map cave passages in all three dimensions, not unlike the drones that can be seen exploring an alien spaceship in the movie “Prometheus.”
“Once deployed, our sensors automatically create an undirected mesh network, which means that every node is informed about every node around it,” said Fink, who first explained the DDCN concept in a proposal to NASA in 2019.
“They can switch between each other and compensate for dead spots and signal interruptions,” added Mark Tarbell, a co-author of the paper and a senior researcher in Fink’s lab. “If some of them die, there is still connectivity through the remaining nodes, so the mother rover never loses connection to the farthest node in the network.”
Shipping without return
The robust network of communication nodes ensures that all data collected by the robotic explorers will be returned to the mother rover on the surface. Therefore, there’s no need to retrieve the robots after they’ve done their job, said Fink, who published the idea of using teams of expendable mobile robotic surface probes as early as 2014.
“They are designed to be expendable,” he said. “Instead of wasting resources to get them into the cave and back out, it makes more sense to have them go as far as they can go and leave them behind once they’ve accomplished their mission, run out of power, or succumbed to a hostile environment. .”
“The communication network approach introduced in this new paper has the potential to herald a new era of planetary and astrobiological discoveries,” said Dirk Schulze-Makuch, president of the German Astrobiological Society and author of several publications on extraterrestrial life. “It ultimately allows us to explore the lava tube caves of Mars and the subsurface oceans of icy moons — places where alien life might exist.”
The proposed idea “holds magic,” according to Victor Baker, UArizona Regents Professor of Hydrology and Atmospheric, Earth, and Planetary Sciences.” or place and means of communicating what is thus discovered to creative minds seeking understanding.” Baker said.
Exploring the hidden worlds of the oceans
In places that require underwater robots, the system could consist of a lander—either floating in a lake, as on Titan, or sitting on ice atop an underground ocean as in Europa—that connects to the sub, for example in by a long cable. Here the communication nodes would act as repeaters, boosting the signal at regular intervals to prevent it from degrading. Importantly, Fink pointed out, the nodes have the ability to collect data themselves — for example, by measuring pressure, salinity, temperature and other chemical and physical parameters — and feed that data into the cable that connects back to the Lander.
“Imagine you get all the way to Europa, melt your way through miles of ice, go down into the subsurface ocean, where you’re surrounded by alien life, but you have no way to bring data back to the surface. ” he said. “That’s the scenario we have to avoid.”
Having developed the rovers and the communication technology, Fink’s team is now working on building the actual mechanism by which the rovers will deploy the communication hubs.
“Basically, we’re going to teach our ‘Hansels’ and ‘Gretels’ how to drop the crumbs so that a functional communication network is created,” Fink said.