JPL Tests Prototype Rover for Future Moon and Mars Missions

NASA is testing advanced mobility and autonomy capabilities on ERNEST, a compact rover prototype developed at the agency’s Jet Propulsion Laboratory, as engineers examine how future vehicles might travel farther across rugged terrain on the Moon and Mars.

The four-wheeled rover, whose full name is Exploration Rover for Navigating Extreme Sloped Terrain, recently traveled about 16 miles, or 26 kilometers, across a stretch of the Colorado Desert in Southern California with minimal intervention from engineers, according to a June 18 NASA report. The test is part of an effort to refine hardware and software that could one day be used on future lunar or Martian rover missions. 

NASA described ERNEST as a prototype and testbed for possible future missions requiring higher speeds, longer distances and more capable navigation than current planetary rovers can achieve. 

Developed at JPL in Southern California, ERNEST is about 4 feet long and is designed to tackle terrain that could challenge NASA’s existing Mars rovers, Curiosity and Perseverance. Unlike those six-wheeled rovers, ERNEST can lift each of its mesh wheels to move past obstacles. It also has enhanced independent decision-making capabilities intended to help it operate across difficult landscapes. 

NASA said the mobility and autonomy advances being tested on ERNEST could be used to inform future rover designs for areas of the Moon or Mars that are now difficult or inaccessible. 

“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.

During the recent desert campaign, ERNEST traveled at speeds of up to 0.6 mph over 37 hours of driving across seven days of intermittent testing. NASA said that speed is an order of magnitude above the top speed at which Curiosity and Perseverance can navigate. 

In images released by NASA/JPL-Caltech from the seven-day field campaign, engineers from JPL are shown setting up illuminators after transporting ERNEST for a pre-sunrise test. 

Nesnas’ team is using ERNEST to demonstrate that it may be possible to build a rover twice the size of the prototype for a long-distance Moon mission. 

“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 for the JPL team that developed ERNEST was mechanical: to design a relatively simple, low-cost rover that builds on the rocker-bogie suspension system used on every NASA Mars rover since Sojourner. That passive suspension system keeps relatively constant weight on all six wheels through pivot points and struts that allow each wheel to adapt to changing terrain. 

ERNEST uses an active suspension system that lets the rover manage weight distribution among its wheels. Two powered joints in front articulate a gimbal, allowing the rover to move with different gaits, including squirming, wheel-walking and obstacle-climbing. A clutch mechanism allows the rover to switch between active and passive suspension. NASA said passive suspension is less capable on difficult terrain but more energy efficient. 

The rover’s four steerable wheels also allow it to 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 the current version of ERNEST was built, the team developed two smaller prototypes, each about 2 feet long, to test 11 active suspension configurations. Engineers ran experiments over several months in a trailer filled with lunar regolith simulant, testing the designs at different slope angles before choosing a final configuration. 

The team then scaled up the rover and added a rectangular head mounted on a 4.5-foot mast. The hardware was completed in September 2024, but the rover initially still required a human operator using a joystick to send movement commands. 

To advance the rover’s autonomy, the ERNEST team used reinforcement learning, a form of artificial intelligence in which a robot learns by interacting with its environment. JPL’s Dynamics and Real-Time Simulation Laboratory developed a high-fidelity virtual testing environment that replicated the rover’s behavior. Engineers fed the simulator data collected from the physical rover as it responded to various terrain types.

Using a high-performance computing cluster, the team ran many simulations at once, sometimes completing thousands of hours of virtual testing over a single weekend, according to NASA. 

After months of virtual training, the team tested whether ERNEST could use its autonomous algorithms to drive over terrain features that would stop a passive-suspension rover. Engineers set up an obstacle course with sand ripples, rubble piles, steps and steep slopes in JPL’s Mars Yard, an outdoor terrain proving ground. NASA said the rover maneuvered through the course on its own and has since completed many similar courses. 

Nayar’s team is now starting a new autonomy project that will integrate the rover’s ability to decide when and how to use its active suspension with longer-range intelligent navigation. The goal is to help ERNEST plan efficient paths so it can tackle surmountable obstacles and go around hazardous ones. 

Work on ERNEST began in 2022 with initial support from JPL internal research and development funds. NASA said the project is now funded by the agency’s Mars Exploration Program and by the Exploration Science Strategy and Integration Office in NASA’s Science Mission Directorate at NASA Headquarters in Washington. 

Caltech in Pasadena manages JPL for NASA.