Hansel and Gretel Rovers, Dropping Wireless Mesh "Breadcrumbs," Could Map the Caves of Mars

Researchers from the University of Arizona's College of Engineering have turned to the story of Hansel and Gretel to develop a system designed to let autonomous vehicles scout Martian caves ahead of human explorers landing on the planet.

"If you remember the book, you know how Hansel and Gretel dropped breadcrumbs to make sure they'd find their way back," says Wolgang Fink, associate professor and the founder and director of the Visual and Autonomous Exploration Systems Research Laboratory at Caltech and the Universoty of Arizona. "In our scenario, the 'breadcrumbs' are miniaturized sensors that piggyback on the rovers, which deploy the sensors as they traverse a cave or other subsurface environment."

The idea behind the approach: scouting out caves and tunnels which could potentially make ideal bases of operation for human occupation of the Red Planet in the future. "Lava tubes and caves would make perfect habitats for astronauts because you don't have to build a structure," Fink explains. "You are shielded from harmful cosmic radiation, so all you need to do is make it pretty and cozy."

The Hansel and Gretel-inspired autonomous exploration system sees tracked rovers dropping wireless communication nodes as it explores, based on an "opportunistic deployment" schedule — meaning that a node is only dropped when the robot's signal is weakening, rather than on a time or distance base. A "mother rover" monitors the exploration rovers through the nodes, either receiving data passively or taking direct control when required.

"Once deployed, our sensors automatically establish a non-directed mesh network, which means each node updates itself about each node around it," Fink explains. "They can switch between each other and compensate for dead spots and signal blackouts," adds co-author and senior research scientist Mark Tarbell. "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."

Where Hansel and Gretel's breadcrumb trail was used by the pair to find their way safely home, however, the rovers may not be so lucky. "They're designed to be expendable," Fink admits. "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 team's work has been published in the journal Advances in Space Research under closed-access terms; with the concept and communication system developed, the next stage is creation of a physical rover prototype capable of deploying the sensor nodes on-demand.

Main article image courtesy ofMark Tarbell and Wolfgang Fink/University of Arizona, based on an original photo by John Fowler.