At a Glance
- Current Earth-based testing of extraterrestrial rovers often yields overly optimistic results about vehicle performance, as evidenced by the Spirit rover’s permanent stalling on Mars in 2009.
- The traditional testing method of using a lightweight rover prototype overlooks how Earth’s stronger gravity compacts sand, making it firmer than the “fluffier” soil on other worlds.
- Researchers at the University of Wisconsin–Madison utilized an advanced physics simulator to determine that low-gravity terrain offers significantly less traction than standard Earth-based tests would suggest.
- This discovery was made with Project Chrono, an open-source simulation software that accurately models the complex interactions between a vehicle and granular terrain in low-gravity environments.
- The findings, published in the Journal of Field Robotics, will help engineers develop more reliable rovers and prevent future missions from failing due to mobility issues.
When NASA’s Spirit rover became permanently stuck in soft Martian soil in 2009, it highlighted a critical challenge in planetary exploration: predicting how a vehicle will perform on an alien world. For decades, engineers have tested rovers on Earth to prevent such multimillion-dollar crises. However, new research from the University of Wisconsin–Madison reveals a fundamental flaw in this long-standing method, suggesting our tests have been overly optimistic. The findings, published in the Journal of Field Robotics, point to a simple but overlooked factor that could reshape how we prepare for future missions to the moon, Mars, and beyond.
The standard approach to testing has been to simulate the weaker gravity of other worlds, such as the moon, where the pull is six times less than Earth’s, by using a rover prototype that is six times lighter. While this accounts for the gravitational force on the vehicle, engineers discovered it ignores the effect of Earth’s gravity on the test environment itself. On Earth, the stronger gravitational pull compacts sand and soil, making it firmer and more supportive. In contrast, the soil on the moon is significantly “fluffier” and shifts more easily, reducing a rover’s traction and making it harder to navigate.
This crucial insight was uncovered using Project Chrono, a powerful, open-source physics simulation engine developed at UW–Madison. Led by mechanical engineering professor Dan Negrut, the research team created virtual models to simulate the mobility of NASA’s Volatiles Investigating Polar Exploration Rover (VIPER). The simulations showed a significant difference between how the rover performed on Earth-based test beds versus how it would actually behave on the moon’s low-gravity, granular surface. The software accurately modeled the complex physics of both the rover and the shifting soil particles, revealing the fallacy of simply reducing the rover’s weight.
The team’s work underscores the importance of advanced, physics-based simulations in designing and testing the next generation of extraterrestrial vehicles. By accurately modeling the low-gravity conditions of both the rover and its environment, engineers can better anticipate and address mobility challenges before a mission ever launches. Project Chrono is publicly available and is also used to solve complex engineering problems on Earth, from designing U.S. Army vehicles to analyzing precision mechanical watches, demonstrating the wide-reaching impact of this university-led research.
References
- Hu, W., Li, P., Rogg, A., Schepelmann, A., Chandler, S., Kamrin, K., & Negrut, D. (2025). A study demonstrating that using gravitational offset to prepare extraterrestrial mobility missions is misleading. Journal of Field Robotics, rob.22597. https://doi.org/10.1002/rob.22597
- Malecek, A. & University of Wisconsin-Madison. (2025, July 26). Robotic space rovers keep getting stuck. Engineers have figured out why. Tech Xplore; University of Wisconsin-Madison. https://techxplore.com/news/2025-07-robotic-space-rovers-stuck-figured.html
