Teamwork truly does make the dream work — at least for legged robots tasked with collecting and analyzing geologic samples peppered throughout coarse and unstable terrain.
New work published in Science Robotics shows how three four-legged robots collaborated to speedily and thoroughly accomplish scientific missions on lunar-like terrain. Scientists gave each robot a distinct job related to scouting, gathering or analyzing data, enabling the collective team to finish processing geologic samples faster than a single robot could.
They were also careful not to make the robots too specialized. Each robot could be repurposed to perform their counterparts' jobs in times of emergency, maintaining a concept known as redundancy.
"Although robots are becoming more and more reliable in challenging and unknown environments, we can never be 100% sure that they do not fail. This is why redundancy is important: Even if one of the robots fails, the other two are still able to finish the mission successfully," said Philip Arm, a researcher at ETH Zürich Robotic Systems Lab and first author of the study.
Through this Goldilocks-esque balance between redundancy and efficiency, the robot team successfully accomplished various goals on lunar-like terrain during the European Space Agency's Space Resources Challenge. The robots also nimbly scuttled through a Martian-like soil bed that has been previously used to test an ExoMars rover's locomotion.
Dexterity, Collaboration and Redundancy
When exploring planetary surfaces, wheeled rovers must move across rocky terrain while avoiding tripping and damaging irreparable parts. Historically, this has posed a problem. During the Apollo 15 mission, astronauts had to dig out their lunar roving vehicle from lunar regolith. In 2009, the rover Spirit became permanently trapped in Martian soil. So now roboticists want to build legged robots that can better traverse the challenges posed by such landscapes.
"Legged robots provide unique benefits in planetary exploration. They allow us to reach scientifically very interesting terrain that so far we had no access to, because of the limitation of wheeled robots," said Hendrik Kolvenbach, a roboticist at ETH Zürich Robotic Systems Lab and author on the study.
Beyond lacking dexterity, wheeled rovers often operate solo during data collection, which further extends the time that any given scientific mission takes. For example, although the Mars Perseverance rover receives some help scouting scientific targets of interest from the Ingenuity helicopter, it still must gather its samples alone.
"Robotic teams are effective in doing planetary exploration missions, because tasks can be parallelized and the robots can be specialized for certain tasks while still being redundant," said Kolvenbach. "The robotic team is more effective than the sum of its individuals."
For these reasons, Kolvenbach, Arm and their colleagues decided to create a team of legged robots that could more easily navigate surface obstacles, collaborate to optimize missions and fill in for each other if one's equipment failed. The group hoped this approach might streamline planetary robotic exploration.
The Scout, The Hybrid and The Scientist
To create their robot team of three, the researchers used the previously designed, four-legged "ANYmal" robot for its agility.
"We customize[d] both the hardware and the software of the robot to conduct research on locomotion, navigation, manipulation, and more in challenging and uncertain environments," said Kolvenbach.
One robot acted as a scout, quickly scrutinizing environments for areas of interest. Another served as a hybrid that could collect samples from flagged targets and sometimes performed data analysis. The third robot behaved as a scientist, primarily dedicated to measuring and imaging samples provided to it by the hybrid. During the Space Resources Challenge in September 2022, this divvying-up of roles proved particularly useful as the robots trekked across 1,800 square meters of ground covered in clay, silt and basalt on a quest for resource-enriched areas.
"While the scout was mapping the environment, we could mark potentially interesting targets based on the map and the camera images, namely seven boulders and 18 terrain patches that looked interesting," said Arm. "Afterwards, we investigated most of these targets using the scientific instruments on the hybrid and the scientist, which allowed our geology team to draw first conclusions on what the material might be."
Overall, the robot team mapped 95% of the competition area and investigated six of those 18 intriguing and seemingly resource-enriched patches. In particular, the scientist robot was able to perform analyses every three to five minutes, which the authors acknowledge would have been impossible if attempted by a single legged robot. Further tests of the robotic team on Mars-like ground emphasized its locomotive agility.
Moving forward, the group now wants to incorporate additional robots into the team, perhaps adding flying robots and the classic, trusty wheeled ones.
"Furthermore, we want to strengthen the autonomy of the robots, so that they can perform target identification and decision making on the fly, reducing operator overhead," said Kolvenbach. "A major aspect is also field validation of the technologies, so that we increase visibility and likelihood of implementation in future missions."