Study shows how to keep a Mars tumbleweed rover moving on rocky terrain

May 23, 2012, North Carolina State University
This is a model of a tumbleweed rover. Credit: North Carolina State University

New research from North Carolina State University shows that a wind-driven "tumbleweed" Mars rover would be capable of moving across rocky Martian terrain – findings that could also help the National Aeronautics and Space Administration (NASA) design the best possible vehicle.

"There is quite a bit of interest within NASA to pursue the tumbleweed rover design, but one of the questions regarding the concept is how it might perform on the rocky surface of Mars," says Dr. Andre Mazzoleni, an associate professor of mechanical and aerospace engineering (MAE) at NC State and co-author of a paper describing the research. "We set out to address that question."

Mazzoleni and Dr. Alexander Hartl, an adjunct professor of MAE at NC State, developed a computer model to determine how varying the diameter and mass of a tumbleweed rover would affect its speed and ability to avoid getting stuck in Martian rock fields. Rock fields are common on the surface of Mars, which averages one rock per square meter.

"We found that, in general, the larger the diameter, and the lower the overall weight, the better the rover performs," Mazzoleni says. In addition, the study found that a tumbleweed rover would need to have a diameter of at least six meters in order to achieve an acceptable level of performance – meaning the rover could move through rock fields without getting stuck.

The surface of Mars averages one rock per square meter. Credit: NASA

Using the model, the researchers also found that tumbleweed rovers are more likely to bounce than roll across the surface, due to the spacing of the rocks and the size of the rovers.

"Computer simulations are crucial for designing because the only place where you find Martian conditions is on Mars," says Mazzoleni. "Earth-based testing alone cannot establish whether a particular design will work on Mars." Mars has approximately three-eighths of Earth's gravity. And the atmospheric density on the surface of Mars is only duplicated around 100,000 feet above the Earth's surface.

Tumbleweed rovers are attractive because they can cover much larger distances, and handle rougher terrain, than the rovers that have already been sent to – such as Spirit and Opportunity. "This model is a tool NASA can use to assess the viability of different designs before devoting the time and expense necessary to build prototypes," Mazzoleni says.

While tumbleweed rovers would lack the precise controls of the wheeled rovers, they would also not rely on a power supply for mobility – they would be literally blown across the Martian landscape by the wind.

Explore further: On a roll: Designing the next rover to explore Mars

More information: The paper, "Terrain Modeling and Simulation of a Tumbleweed Rover Traversing Martian Rock Fields," is published in the March/April issue of the Journal of Spacecraft and Rockets. Hartl is lead author.

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1 / 5 (1) May 23, 2012
helium balloon
4 / 5 (1) May 23, 2012
TopCat22 - great idea - I'll expand on it by stating that the balloon should be able to be deflated or inflated according to need - if the rover gets stuck, it would be inflated just enough to lift the rover over the obstruction, then deflated to let if back down. A small compressor could suck the helium back into a storage bottle so the amount sent to Mars with the rover would get the longest possible usage time. The rover could monitor wind conditions so that if it needed a boost to a particular location, the balloon could be deployed and the rover would then lift up and float along until the new destination is reached. Then the balloon would deflate and lower the rover into position.
not rated yet May 23, 2012
You are making the assumption that helium is will be lighter than air on the surface... while probably true remember that Mars has no sealevel -- and at best air pressure is no where near 1 atmosphere.
3 / 5 (2) May 23, 2012
bigger helium balloon
1 / 5 (3) May 23, 2012
bigger helium balloon

Size doesn't matter if helium is denser than the martian atmosphere.
5 / 5 (1) May 23, 2012
Helium has only 9% of the density of carbon dioxide at any given pressure. Mars's atmosphere is 95% CO2.
not rated yet May 23, 2012
Valid point Silverhill, except that composition of C02 is not the same as density. If the Martian atmosphere is too thin, then a balloon inflated with helium at a relatively high density might still weigh more than the surrounding atmosphere, although presumably less pressure would be needed to inflate it. Use of a gas to inflate a rover to roll or bounce across Mars is still a valid idea though, just don't expect it to float and stay up there. NASA has been working on variations of the Tumbleweed rover for some time.
Lex Talonis
1 / 5 (2) May 23, 2012
The tumbeweed rovers ought to be about 20 or 30 meters in diameter.

The main issue I see is durability of the rolling surface..... I mean it all wears out eventually - but getting the most amount of distance out of it, with the most durable rolling surface possible would be good, in terms of mission life and distance travelled....

That is until it rolls into some great big hole of some description.

Rather remote though.
not rated yet May 24, 2012
Yeah, and how do you stop the rover to make any accurate measurements? Or take photos?
3 / 5 (2) May 24, 2012
We found that, in general, the larger the diameter, and the lower the overall weight, the better the rover performs
So, lighter and bigger objects are likelier to blow around in the wind? I hope they didn't spend too much effort figuring that one out.
not rated yet May 24, 2012
How quickly will helium diffuse through the balloon material? Methinks designing a balloon to contain helium for an extended mission would be very difficult.

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