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.
ERNEST serves as a testbed for a potential future lunar rover mission
requiring high speeds and extreme distances. In a recent field test, the
prototype traveled 16 miles over the course of 37 hours, going an order of
magnitude above the top speed at which NASA’s current Mars rovers can navigate.
Credit: NASA/JPL-Caltech
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.
Engineers from JPL set up illuminators after
transporting ERNEST for a pre-sunrise test during a seven-day desert field
campaign.
NASA/JPL-Caltech
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.
The
mobility and autonomy advances developed at JPL for the ERNEST prototype rover
could be infused into future NASA missions to previously inaccessible areas of
the Red Planet or the Moon. Credit: NASA/JPL-Caltech
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.
Source: NASA
Testing Advanced Capabilities for Moon, Mars Rovers - NASA
