Making tracks in the desert

The ground was dry, dusty, and rocky, with small rolling hills, peppered with the track marks of a rover. The place could have been the surface of Mars except that the sky was a bright, cloudless blue, and the temperature had reached 90 degrees. Catherine Pavlov was in the Atacama Desert in Chile, the driest non-polar desert on Earth and one of the best analogs for Mars on the planet.

Pavlov, the winner of a competitive NASA Space Technology Research Fellowship, was in the dry heat of the Atacama conducting experiments that aim to add additional functionality to space rovers. Pavlov’s research centers around non-prehensile terrain manipulation, or put more simply, using non-grasping methods to interact with terrain. Basic examples of general non-prehensile manipulation include moving a ping pong ball with paddles and a robot using its arm to clear a table.

“I look at how we can use the wheels of planetary exploration rovers to modify the environment around them,” said Pavlov, a Ph.D. candidate in mechanical engineering advised by MechE Assistant Professor Aaron Johnson. “We are trying to expand what rovers can do both in a manipulation context and a mobility context.”

Robotics systems used in space missions are extremely costly and made to optimize functionality and reliability while being lightweight and fuel-efficient. Adding a manipulator, with multiple motors and sensors,adds mass and complexity, two big things to avoid for space missions. Mass directly increases launch cost and requires more fuel.

We are trying to expand what rovers can do both in a manipulation context and a mobility context.

Catherine Pavlov, Ph.D. Candidate, Mechanical Engineering

Via non-prehensile terrain manipulation, Pavlov is exploring how to utilize existing interactions with the world that were previously considered disturbances or accidents and use them intentionally. Rather than see wheel tracks on the ground as a consequence of driving, Pavlov treats the ground as a target for modification. In her research, she investigates how the rover’s wheel-terrain interaction can be used to move along slopes by leveling paths, making terrain compact, and removing material.

Pavlov developed a new model for this research. While models already exist for wheel-terrain situations, they focus on the mobility and driving ability of the vehicles, not the movement of the soil. Pavlov uses terramechanics to predict how deep a wheel sinks, so that her new model can predict where the soil goes after the wheel passes over it and the shape of the remaining trench.

In the summer of 2019, Pavlov spent time at NASA Ames, a major NASA research center in Silicon Valley, as part of the fellowship program. There, she worked in model development and interfaced with rover software to set up sensors to track the rover in real time. In September, she joined NASA researchers in the Atacama Desert to test her model on the experimental KREX-2 rover in an environment similar to Mars. With little wild- or plant-life and a rocky terrain of shallow slopes, the environment was a great substitute for Mars.

“The trenching experiments went well. This was the first time we tested it on a substrate that actually looks something like what we might expect to see on Mars. It was awesome to see it work.” Pavlov presented her research in a poster session at NASA’s research grant day on Capitol Hill in December 2019.

Currently in her fourth year of the Ph.D. program, Pavlov sees several different avenues for the future of the project, including variations in wheel and rover design, expanding to other terrain types, and adding other terrain manipulators. Conducting experiments at NASA Ames and the Atacama Desert gave her the opportunity to get out into the field, and Pavlov is looking forward to continuing her research.