Legged Robots & Lunar Soil: Douglas Jerolmack on NASA’s LASSIE & TRUSSES Projects

Susan Wise: Hi, and welcome to Stars Launch Pod: Space Technology and Research Sciences, brought to you by StarSciences.org, where we connect, collaborate, and accelerate. I’m your host, Susan Wise, and I’m honored to have with us today Douglas Jerolmack, professor of Earth and Environmental Science, and Mechanical Engineering and Applied Mechanics.
Hi, Douglas. Welcome to the show.

Douglas Jerolmack (he/him): Hi. Thanks for having me.

Susan Wise: Well, I’d love to hear a little bit more about what you’re doing right now and how it’s furthering the space industry.

Douglas Jerolmack (he/him): Sure. I should start by saying I’m a geophysicist, and most of my research is grounded here on planet Earth. We do a lot of experiments and some fieldwork. But I don’t discriminate among planets in terms of interests. I like to say that I do a lot of work on Earth because it’s right in front of me—it’s a little harder to do work farther out.

But when there are fascinating patterns and landscapes on other planets, we go for that. Right now, we’re working on two planetary projects funded by NASA. One of them is called the LASSIE Project. Our team is advocating for getting robots with legs onto other planets.

Susan Wise: Yes, I’ve seen those. They’re so cool—like little puppies!

Douglas Jerolmack (he/him): Yeah, that’s right—they’re little robot dogs. Wheels are great on firm, flat terrain, and you can load heavy equipment on wheeled platforms. That’s why all rovers we’ve put on other planets have wheels. But the moment you encounter loose soil or even slightly steep slopes, engineers are screaming, “Stay away! Stay away!” That means you can’t reach scientifically interesting areas.

Of course, humans are also interested in returning to the Moon and even Mars. That means we’ll need to move across, understand, and manipulate foreign soil. Robots with legs can climb steep slopes and move through loose soil without getting stuck, like you and I can—or like dogs can. They can act as scouts, showing astronauts where to build roads or where wheeled rovers could safely follow.

The big idea, though, is that the legs themselves are sensors. They can feel how strong or weak the soil is. A legged robot can carry instruments, like other rovers, but the robot itself is also an instrument. As its legs push into the soil, we can measure the force pushing back and learn how strong, weak, sticky—or even squishy—the soil is.

That’s one of our major projects: showing that legged robots can both access difficult areas and serve as scientific instruments to study lunar soil. That’s the LASSIE Project.

Susan Wise: Of course—now I get it!

Douglas Jerolmack (he/him): You got it. And LASSIE now has a sister project called TRUSSES. In that one, we’re exploring teams of robots—some with wheels, some with legs. The question is: if humans and robots are exploring the Moon or Mars together, how do we deploy different types of robots most effectively? Can robot teams operate separately, but also come together to pull one another out of sand traps when they get stuck?

There’s a lot of technological development in that. My role always comes back to the physics and mechanics of the soil and how that plays into these problems. Those are the two major NASA projects we’re working on.

Susan Wise: Do you actually get to work with soil from the Moon?

Douglas Jerolmack (he/him): No. The quantities we’d need are too large to request from the precious Apollo samples. Instead, we use lunar regolith simulant. Scientists analyzed the Apollo soil samples, then recreated synthetic soil by grinding volcanic minerals and rocks. It mimics the lunar soil in particle size, consistency, and its mix of coarse grains and sticky, abrasive dust.

We experiment with that, but also with spherical glass beads, beach sand, and mud. Using a range of materials helps us understand how soil consistency affects robot locomotion.

Susan Wise: That way you’re ready for any environment. What’s been one of your biggest “aha” moments?

Douglas Jerolmack (he/him): One came from these projects. This collaboration started around 2013 or 2014, when robotics professor Dan Koditschek at Penn approached me. He’d been working on legged robots and wondered if they could help with desert science. At first, I thought carrying instruments was something my students could already do. But as I learned how the robot legs worked, I had a realization.

Unlike cars, which have gears and friction separating the motor from the wheels, these legs are direct drive—the motor moves and the leg moves. That means the motor’s voltage actually measures the resistance of the ground. When the ground is soft, the robot struggles and needs more power. That was the “aha” moment: the motor itself could be a scientific instrument. The robot could measure soil strength just by walking.

Of course, everything that makes the legs more sensitive for science makes them worse at walking. So there was constant tension between science and engineering. It took us over 10 years to get to the point where a walking robot could also deliver science-grade measurements.

Susan Wise: So that was one of your biggest challenges?

Douglas Jerolmack (he/him): Absolutely. Technically, it was tough, but the real challenge was persistence. You can’t solve a 10-year problem with one grant. You need to keep spinning off smaller, fundable problems to maintain momentum and launch careers for students and postdocs. Now, though, we can brag a little. Our robots produce measurements NASA is excited about, and we’ve shown they can map hazards in sand dunes, flagging safe and unsafe zones for wheeled rovers.

Susan Wise: That’s amazing.

Douglas Jerolmack (he/him): It is. We’ve demonstrated that legged and wheeled robots can complement each other in planetary exploration.

Susan Wise: What advice would you give our listeners?

Douglas Jerolmack (he/him): Persistence is important, but I’d say the bigger lesson is that science is a human endeavor. It’s all about relationships. To survive a decade of failures, you need encouragement, openness, camaraderie, and community.

I’ve learned to be intentional about nurturing relationships, celebrating successes, and even grieving failures. That human connection not only sustains long-term collaborations but also takes science in unexpected directions. When you prioritize working with people who are curious, joyful, and collaborative, you end up discovering things you never imagined.

Susan Wise: Happily, that’s what Stars Launch Pod is about—connecting, collaborating, and accelerating by bringing people together to share experiences and learn from each other.

Douglas Jerolmack (he/him): Exactly.

Susan Wise: Before we wrap up, do you have a past or present passion project you’d like to share?

Douglas Jerolmack (he/him): I’ll mention two quirky ones. First, with colleagues, we’ve been studying crack patterns on planetary surfaces—everything from mud cracks on Mars to tectonic cracks on Earth to fractures on icy moons. We’ve found that crack geometry carries signatures of whether water was involved. It’s possible to tell, just from the geometry, if water played a role.

Second, we studied baseball “rubbing mud.” For 90 years, Major League Baseball has used a special mud from a secret location in New Jersey to prepare baseballs. MLB has tried to replace it synthetically, without success. We bought some, analyzed it, and published a paper showing why it works—and why it would be very hard to replace. Our recommendation? Don’t. It’s sustainable, replenished by tides, and works perfectly.

Susan Wise: Well, good for that family! Keep that business in the family. I had no idea—who would’ve thought? I love it. Douglas, thank you so much for joining us today. We’d love to hear back from you again in the future.

Douglas Jerolmack (he/him): Anytime. Thank you—this has been a great conversation.

Susan Wise: That was Douglas Jerolmack, professor of Earth and Environmental Science, and Mechanical Engineering and Applied Mechanics at the University of Pennsylvania.

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