Snake-Like Robot for Traversing Extreme Terrain on Earth, Moon, and Beyond

Jet Propulsion Laboratory, Pasadena, CA

Team members from JPL test a snake robot called EELS at a ski resort in the Southern California mountains. Designed to sense its environment, calculate risk, travel, and gather data without real-time human input, EELS could eventually explore destinations throughout the solar system. (Image: NASA/JPL-Caltech)

A team at NASA's Jet Propulsion Laboratory that's creating a snake-like robot for traversing extreme terrain is taking on the challenge with the mentality of a startup: Build quickly, test often, learn, adjust, repeat. Called EELS (short for Exobiology Extant Life Surveyor), the self-propelled, autonomous robot was inspired by a desire to look for signs of life in the ocean hiding below the icy crust of Saturn's moon Enceladus by descending narrow vents in the surface that spew geysers into space.

EELS is tested in the sandy terrain of JPL's Mars Yard. Engineers repeatedly test the snake robot across a variety of terrain, including sand, snow, and ice. (Image: NASA/JPL-Caltech)

Although testing and development continue, designing for such a challenging destination has resulted in a highly adaptable robot. EELS could pick a safe course through a wide variety of terrain on Earth, the Moon, and far beyond, including undulating sand and ice, cliff walls, craters too steep for rovers, underground lava tubes, and labyrinthine spaces within glaciers.

“It has the capability to go to locations where other robots can't go. Though some robots are better at one particular type of terrain or other, the idea for EELS is the ability to do it all,” said JPL's Matthew Robinson, EELS Project Manager. “When you're going places where you don't know what you'll find, you want to send a versatile, risk-aware robot that's prepared for uncertainty — and can make decisions on its own.”

The project team began building the first prototype in 2019 and has been making continual revisions. Since last year, they've been conducting monthly field tests and refining both the hardware and the software that allows EELS to operate autonomously. In its current form, dubbed EELS 1.0, the robot weighs about 220 lbs (100 kgs) and is 13-feet (4 m) long. It's composed of 10 identical segments that rotate, using screw threads for propulsion, traction, and grip. The team has been trying out a variety of screws: white, 8-inch-diameter (20-cm-diameter) 3D-printed plastic screws for testing on looser terrain, and narrower, sharper black metal screws for ice.

Because of the communications lag time between Earth and deep space, EELS is designed to autonomously sense its environment, calculate risk, travel, and gather data with yet-to-be-determined science instruments. When something goes wrong, the goal is for the robot to recover on its own, without human assistance.

EELS creates a 3D map of its surroundings using four pairs of stereo cameras and LiDAR, which is similar to radar but employs short laser pulses instead of radio waves. With the data from those sensors, navigation algorithms figure out the safest path forward. The goal has been to create library of “gaits,” or ways the robot can move in response to terrain challenges, from sidewinding to curling in on itself, a move the team calls “banana.”

In its final form, the robot will contain 48 actuators — essentially little motors — that give it the flexibility to assume multiple configurations but add complexity for both the hardware and software teams. Many of them have built-in force-torque sensing, working like a kind of skin so EELS can feel how much force it's exerting on terrain. That helps it to move vertically in narrow chutes with uneven surfaces, configuring itself to push against opposing walls at the same time like a rock climber.

The robot has been put to the test in sandy, snowy, and icy environments, from the Mars Yard at JPL to a “robot playground” created at a ski resort in the snowy mountains of Southern California, even at a local indoor ice rink.

For more information, contact Melissa Pamer at This email address is being protected from spambots. You need JavaScript enabled to view it.; 626-314-4928.