Hansel and Gretel’s ‘breadcrumb trick’ inspires robotic exploration of caves on Mars that could potentially house astronauts

University of Arizona engineers have developed a system that allows autonomous vehicles to scout out underground habitats for astronauts, such as those that might set foot on Mars.

Wolfgang Fink, an associate professor of electrical and computer engineering at UArizona, said: “Lava tubes and caves would make perfect habitats for astronauts because you don’t have to build a structure; you are shielded from harmful cosmic radiation, so all you need to do is make it pretty and cosy.”

Fink is the lead author of a new paper that details a communication network that would link rovers, lake landers, and even submersible vehicles through a so-called mesh topology network, allowing the machines to work together as a team, independently from human input.

According to Fink and his co-authors, the approach could 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 fairy tale Hansel and Gretel, the researchers named their patent-pending concept the “Breadcrumb-Style Dynamically Deployed Communication Network” paradigm, or DDCN.

Fink, who is founder and director of the Visual and Autonomous Exploration Systems Research Laboratory at Caltech and UArizona, explained: “If you remember the book, you know how Hansel and Gretel dropped breadcrumbs to make sure they’d find their way back.

“In our scenario, the ‘breadcrumbs’ are miniaturised sensors that piggyback on the rovers, which deploy the sensors as they traverse a cave or other subsurface environment.”

Continuously monitoring their environment and maintaining awareness of where they are in space, the rovers proceed on their own, connected to each other via a wireless data connection, deploying communication nodes along the way.

Once a rover senses the signal is fading but still within range, it drops a communication node, regardless of how much distance has actually passed since it placed the last node.

See also: Perseverance studies Mars meteorology


Robotic explorers


Fink added: “One of the new aspects is what we call ‘opportunistic deployment’ – the idea that you deploy the breadcrumbs when you have to and not according to a previously planned schedule.”

There is no need for input from the mother rover; each subordinate rover will make that determination on its own. The system can work in one of two ways: in one, the mother rover acts as a passive recipient, collecting data transmitted by the rovers doing the exploration; and in the other, the mother rover acts as the orchestrator, controlling the rovers’ moves like a puppet master.

The new concept dovetails with the tier-scalable reconnaissance paradigm devised by Fink and colleagues in the early 2000s.

This idea envisions a team of robots operating at different command levels – 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 concept, several with participation by UArizona researchers. For example, on Mars, the Perseverance rover is commanding Ingenuity, a robotic helicopter.

The breadcrumb approach takes the idea one step further by providing a robust platform allowing robotic explorers to operate underground or even submerged in liquid environments. Such swarms of individual, autonomous robots could also aid in search and rescue efforts in the wake of natural disasters on Earth.





Fink said the biggest challenge, apart from getting the rovers inside the subsurface environment in the first place, is to retrieve the data they record underground and bring it back to the surface.

The DDCN concept allows a team of rovers to navigate even convoluted underground environments without ever losing contact with their ‘mother rover’ on the surface. Outfitted with a light detection and ranging system, or lidar, they could even map out cave passages in all three dimensions.

Fink advised: “Once deployed, our sensors automatically establish a non-directed mesh network, which means each node updates itself about each node around it.

Mark Tarbell, paper co-author and senior research scientist in Fink’s laboratory, said: “They can switch between each other and compensate for dead spots and signal blackouts. If some of them ‘die’, there still is connectivity through the remaining nodes, so the mother rover never loses connection to the farthest node in the network.”

The robust network of communication nodes ensures all the data collected by the robotic explorers make it back to the mother rover on the surface. Therefore, there is no need to retrieve the robots once they have done their job.

Fink said: “They’re designed to be expendable. 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 possibly can and leave them behind once they have fulfilled their mission, run out of power or succumbed to a hostile environment.”

The paper is published in Advances in Space Research.

Image 1: In this artist’s impression of the breadcrumb scenario, autonomous rovers can be seen exploring a lava tube after being deployed by a mother rover that remains at the entrance to maintain contact with an orbiter or a blimp. © Photo: John Fowler/ Creative Commons (CC BY). Mark Tarbell and Wolfgang Fink/ University of Arizona.

Image 2: A hole in the surface of Mars, spotted by the HiRISE camera, reveals a cave below. Protected from the harsh surface of Mars, such pits are believed to be good candidates to contain Martian life, making them prime targets for possible future spacecraft, robots and even human interplanetary explorers. © NASA/ JPL/ University of Arizona. Public domain.

Image 3: One of the experimental rovers used by Fink’s team to test hardware and software related to autonomous exploration. This prototype is outfitted with cameras and other sensors for navigation. © Wolfgang Fink/ University of Arizona.