Engineers at the University of Wisconsin–Madison have identified a key limitation in how planetary rovers are tested on Earth, which may help explain why these vehicles can become immobilized during extraterrestrial missions. The findings, published in the Journal of Field Robotics, stem from computer simulations revealing that conventional Earth-based rover tests do not accurately replicate the interaction between a rover and loose terrain under low-gravity conditions.
Rovers such as NASA’s Spirit, which became permanently stuck in soft soil on Mars in 2009, typically undergo terrestrial testing in environments like desert sand. To simulate the reduced gravity of the moon or Mars, researchers traditionally reduce the mass of prototype rovers by a corresponding factor. However, this method does not account for the unchanged gravitational pull Earth exerts on the sand or soil used in these tests.
Dan Negrut, a professor of mechanical engineering at UW–Madison, and his research team demonstrated through simulation that Earth’s gravity increases the rigidity of sand, offering more resistance to vehicle movement compared to lunar or Martian terrain. As a result, rovers tested on Earth may appear more capable than they actually are once deployed on extraterrestrial missions where the surface is more prone to shifting and slippage due to lower gravity.
The research was part of a NASA-funded project aimed at simulating the VIPER rover, a vehicle intended for lunar exploration. The team used Project Chrono, an open-source physics simulation engine developed at UW–Madison in collaboration with researchers in Italy. The simulation platform enabled detailed modeling of rover mobility over soft terrain in low-gravity environments and exposed inconsistencies between terrestrial tests and simulated lunar performance.
Chrono, which is publicly available and used by hundreds of organizations, has applications beyond space exploration. It has been employed to simulate mechanical systems in industries ranging from watchmaking to military vehicle testing. The software continues to be maintained and enhanced by the UW–Madison team, supported by funding from NASA, the National Science Foundation, and the U.S. Army Research Office.
Photo credit Joel Hallberg / UW–Madison
