Engineers Uncover Flaws in Testing Robotic Rovers for Space Missions

Engineers at the University of Wisconsin-Madison have identified critical flaws in the testing methods used for robotic space rovers, which have resulted in these multimillion-dollar machines frequently getting stuck in soft extraterrestrial terrains. The findings, published in the *Journal of Field Robotics* on July 26, 2025, highlight that current testing protocols fail to accurately simulate the conditions rovers will encounter on the Moon and Mars, leading to overly optimistic predictions about their mobility.

The study, led by Dr. Dan Negrut, Professor of Mechanical Engineering at the University of Wisconsin-Madison, demonstrates that the gravitational differences between Earth and other celestial bodies significantly affect how granular materials, such as sand, behave. Traditional testing methods have involved creating prototypes that weigh one-sixth of the actual rover's mass to simulate reduced gravity conditions. However, this approach has overlooked the critical impact of Earth's gravity, which causes sand to behave more rigidly than it would in the lower gravity environments of the Moon or Mars.

Negrut and his collaborators utilized Project Chrono, an open-source physics simulation engine developed at UW-Madison, to explore these discrepancies. They found that while Earth-based tests suggest that rovers can navigate sandy terrains without issue, the reality on extraterrestrial surfaces is far different. The Moon's soil, described as "fluffier," shifts more readily, reducing the traction available to rovers and increasing the risk of becoming stuck.

"In retrospect, the idea is simple: We need to consider not only the gravitational pull on the rover but also the effect of gravity on the sand to get a better picture of how the rover will perform on the Moon," Negrut stated. His findings indicate a need to revise existing testing protocols to incorporate these insights, which could enhance the success rate of future missions.

The implications of this research extend beyond space exploration. The techniques developed through Project Chrono have applications on Earth as well, aiding organizations in understanding complex mechanical systems ranging from military vehicles to consumer products. Negrut emphasized the importance of continuous innovation in simulation software, noting that the open-source nature of Project Chrono allows others to adopt and adapt their findings quickly.

Co-authors of the study include Wei Hu from Shanghai Jiao Tong University, Pei Li from UW-Madison, and researchers from NASA and other institutions, all contributing to a comprehensive understanding of rover mobility in various terrains. The research has garnered support from the National Science Foundation, the U.S. Army Research Office, and NASA, further underlining its significance in both academic and practical applications.

As NASA prepares for upcoming lunar missions, including the VIPER rover project, these findings will be pivotal in ensuring that future explorations are equipped to handle the unique challenges posed by extraterrestrial terrains. By refining testing methodologies based on these insights, engineers aim to improve the reliability and functionality of robotic explorers tasked with journeying to and conducting research on distant worlds.