Engineers Discover Key Flaw in Space Rover Terrain Testing

When robotic space rovers encounter obstacles on extraterrestrial terrain, they can become immobilized, as demonstrated by the Mars rover Spirit in 2009. Engineers on Earth often intervene to free these vehicles, but a new study by mechanical engineers at the University of Wisconsin–Madison (UW–Madison) reveals a significant flaw in how these rovers are tested before their missions.

The researchers discovered that current testing methods may lead to overly optimistic predictions about a rover’s ability to navigate soft surfaces on celestial bodies, such as the moon or Mars. Their findings, published in the Journal of Field Robotics, underscore the necessity for more accurate simulations to enhance rover mobility.

Uncovering the Testing Flaw

Mechanical engineering professor Dan Negrut and his team utilized computer simulations to analyze the performance of rovers on low-gravity surfaces. Traditionally, engineers have accounted for the moon’s weaker gravitational pull by creating prototypes that weigh one-sixth of the actual rover’s mass. Testing these lightweight models in desert environments was considered sufficient for understanding how they would behave on the moon.

However, Negrut’s research revealed that this approach overlooks a critical detail: the strong influence of Earth’s gravity on sand. On Earth, sand is more compact and supportive compared to the looser, “fluffier” surface found on the moon. This difference means that rovers may experience reduced traction on the moon, increasing the likelihood of becoming stuck in soft terrain.

“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 explained.

Advancements in Simulation Technology

The team conducted their research as part of a NASA-funded project to simulate the VIPER rover, which is intended for a lunar mission. They employed Project Chrono, an open-source physics simulation engine developed at UW–Madison, to model the rover’s interactions with various surfaces.

While simulating the VIPER rover’s movements, the researchers noticed discrepancies between their Earth-based tests and the simulations of its performance on the moon. Further investigation using Project Chrono allowed them to identify the testing flaw that could lead to mission failures.

Negrut emphasized the broader implications of their research, stating, “It’s rewarding that our research is highly relevant in helping to solve many real-world engineering challenges.” The open-source nature of Project Chrono has led to its adoption by numerous organizations, from the aerospace sector to military applications, improving the understanding of complex mechanical systems.

The research has received support from organizations including the National Science Foundation and the U.S. Army Research Office, reflecting its significance in advancing both space exploration and terrestrial engineering.

Negrut highlighted the rarity of producing industrial-strength software from an academic setting, noting, “There are certain types of applications relevant to NASA and planetary exploration where our simulator can solve problems that no other tool can solve.”

As the team continues to innovate and enhance Project Chrono, they aim to keep pace with emerging challenges in both space and Earth-based applications. Their work stands as a testament to the importance of rigorous testing and simulation in ensuring the success of future extraterrestrial missions.