On a bleak stretch of the Colorado Desert in Southern California, a compact four-wheeled rover recently trundled about 16 miles (26 kilometers) with minimal intervention from the team of engineers trailing it. Called ERNEST (Exploration Rover for Navigating Extreme Sloped Terrain), this prototype is being used by NASA to advance both robotic autonomy and the ability to traverse challenging landscapes.

Developed at NASA’s Jet Propulsion Laboratory in Southern California, ERNEST is 4 feet (1.2 meters) long. Not only can it lift each of its mesh wheels to get past obstacles that would stymie Curiosity and Perseverance, NASA’s six-wheeled Mars rovers, but the prototype also has enhanced independent decision-making capabilities. These mobility and autonomy advances could be infused into future missions that will venture to previously inaccessible areas of the Red Planet or the Moon.

In the field, ERNEST served as a testbed for a potential future lunar mission requiring higher speeds and much greater mileage than can be accomplished by current rovers. This technology could be used to inform future designs for exploration efforts on the Moon and beyond.

“This testing is helping us refine the mobility hardware and autonomy software to navigate extreme distances across a wide range of terrain and lighting conditions anticipated on the Moon,” said Issa Nesnas, a principal technologist at JPL who led the recent testing as head of autonomy for a NASA mission concept for a potential future long-range lunar rover.

Nesnas’ team is using ERNEST to demonstrate it is possible to build a rover that’s twice as big as the prototype and capable of a long-distance Moon mission. During the recent campaign, ERNEST traveled at speeds up to 0.6 mph (1 kph) over 37 hours of driving, across seven days of intermittent testing. That’s an order of magnitude above the top speed Perseverance and Curiosity can navigate.

“You could do a science road trip across the Moon — or Mars — with this vehicle,” said James Keane, a JPL planetary scientist working on lunar missions.

The initial goal of the team that developed ERNEST was mechanical: to design a relatively simple, low-cost rover that advances the trusted rocker-bogie suspension system featured on every Mars rover since NASA’s Sojourner. This passive system keeps relatively constant weight on all six wheels, thanks to pivot points and struts that enable each one to adapt to the changing surface.

On ERNEST, the active suspension lets the rover manage weight distribution among its wheels. Two powered joints in front articulate a gimbal that allows the rover to drive using different gaits like squirming, wheel-walking, and obstacle-climbing. With a clutch mechanism, it can switch between active and passive suspension, which is less terrain capable but more energy efficient. With four steerable wheels, it can drive in any direction, including sideways.

“We started by postulating that we could do better in designing a planetary surface robotic mobility system,” said Hari Nayar, a JPL principal technologist leading the ERNEST team. “While the rocker-bogie system has been very successful over the past 30 years, there’s been a lot of research in that time on mobility and understanding terrain interaction.”

Before arriving at today’s version of ERNEST, the team built two earlier prototypes, each about 2 feet (0.6 meters) long, to test 11 active suspension configurations. In a trailer filled with lunar regolith simulant, they ran experiments at different slope angles over several months before landing on a final design.

Then the team scaled up, including adding a rectangular head mounted on a 4.5-foot-tall (1.4-meter-tall) mast. The hardware was completed in September 2024, but the rover still needed a human operator to joystick it, sending commands to instruct the rover on how to move over obstacles.

In order to train the rover to think on its own, the ERNEST team turned to reinforcement learning, a type of artificial intelligence where the robot learns by interacting with its environment. The Dynamics and Real-Time Simulation Laboratory at JPL developed a high-fidelity virtual testing environment that replicates the rover’s behavior. The team fed the simulator data collected by engineers who documented the response of the actual rover hardware to a variety of terrain types. On a high-performance computing cluster, the team ran many simulations at once, sometimes completing thousands of hours of tests over a single weekend.

After months of virtual training, the ERNEST team was ready to see if the rover could use its new autonomous algorithms to figure out how to drive over terrain features that would halt a passive-suspension rover. They set up an obstacle course with sand ripples, rubble piles, steps, and steep slopes in JPL’s Mars Yard, an outdoor terrain proving ground. Then they watched as the rover maneuvered the terrain on its own. Since then, ERNEST has completed many such courses.

Nayar’s team is starting a new autonomy project which involves integrating the rover’s ability to determine when and how to use its active suspension with longer-range intelligent navigation. The goal is to enable ERNEST to plan an efficient path so that it can tackle surmountable obstacles and circumnavigate hazardous ones. These capabilities could contribute to potential future rover missions encountering formidable landscapes on Mars or more rugged areas of the Moon.

Work on ERNEST began in 2022 was initially supported by JPL internal research and development funds. It is currently funded by NASA’s Mars Exploration Program and the agency’s Exploration Science Strategy and Integration Office in its Science Mission Directorate at NASA Headquarters in Washington. Caltech in Pasadena, California, manages JPL for NASA.

Media Contacts

Karen Fox / Molly Wasser
NASA Headquarters, Washington
240-285-5155 / 240-419-1732
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov   

Melissa Pamer
Jet Propulsion Laboratory, Pasadena, Calif.
626-314-4928
melissa.pamer@jpl.nasa.gov

2026-040