NASA’s exploration missions have recently come under scrutiny due to a potential error in how the physics of lunar and Martian surfaces are understood. While working on NASA’s VIPER mission, a team noticed a significant discrepancy in the way the lunar and Martian soil dynamics were modeled during rover testing. This miscalculation may have contributed to past issues, such as the fate of the Spirit rover, which got stuck on Mars when its wheels broke through the planet’s soft sand.
The Physics Behind the Problem
Landing a spacecraft on another celestial body is no small feat, and landing a rover on the Moon or Mars adds additional complexity. Space agencies typically rely on Earth-based tests to simulate rover operations on other planetary surfaces. For years, NASA has used environments like deserts or the specially designed “Mars Yard” at the Jet Propulsion Laboratory (JPL) to conduct these experiments. While these tests have been instrumental in planning missions, a new study suggests they may have led to overly optimistic conclusions.
Bryan Martin, flight software and test beds manager at JPL, emphasized the thoroughness of these tests. “We test a lot of that, figure out what kinds of things to avoid,” he explained. However, the study points out that the current testing methods may not fully account for the significant differences in surface conditions between Earth and other celestial bodies.
Misunderstanding Soil Mechanics
A core issue identified in the study is how NASA and other space agencies approach the testing of rovers in low-gravity environments. Mars, with only 38% of Earth’s gravity, and the Moon, with just 17%, present unique challenges when it comes to soil and terrain interaction. For example, to compensate for Mars’s weaker gravity, scientists reduce the mass of the rovers during testing.
The study points out that NASA has been focusing too heavily on simulating the effect of gravity on the rover itself, neglecting how the weaker gravity affects the soils, sands, and dust on Mars and the Moon. In essence, the soil’s behavior may differ significantly from how it’s modeled on Earth-based terrains, which could lead to miscalculations in rover mobility.
Simulations Offer New Insights
NASA’s now-discontinued VIPER mission, which aimed to explore the Moon’s surface, brought attention to this gap in understanding. Using an open-source physics simulator called Project Chrono, the team at the University of Wisconsin-Madison uncovered a crucial flaw in how the lunar soil was being modeled in the tests. According to Dan Negrut, a professor of mechanical engineering at UW-Madison, “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.”
The results from the simulation revealed that previous rover tests on Earth may have overestimated the trafficability of the lunar and Martian terrain. When the research team compared simulations of rover behavior on the Moon and Earth, they found that the physical properties of the soil were vastly different due to the lower gravity on the lunar surface. This suggests that, in some cases, it may not be necessary to reduce the mass of the rover in Earth tests if the soil conditions are not correctly adjusted to account for the gravity differences.
Reconsidering Rover Design for Future Missions
The new findings could have significant implications for NASA’s future missions. The study advocates for a more sophisticated approach when designing rovers and other exploration vehicles for other planetary bodies. The researchers suggest that space agencies should rely more heavily on physics-based terramechanics models—advanced simulations that take into account not only the effects of gravity on the rover but also on the terrain.
Negrut also highlighted the importance of using advanced simulation tools, stating that such technology is a breakthrough in space exploration. “There are certain types of applications relevant to NASA and planetary exploration where our simulator can solve problems that no other tool can solve,” he said.
Source link
