Last July, I got trapped in that epic dust storm that ripped through Phoenix. My second thought – after I realized my Canadian instinct of "snow!" couldn't be right – was that between the dust and red skies, that is what Mars must look like.Well, Mars might be looking a even more like the southwestern United States in the future, because NASA has expressed interest in sending tumbleweed-inspired rovers to the red planet.New research on these new vehicles comes from North Carolina State University. A group of scientists has shown that these Western-inspired rovers might simplify Martian exploration. Tumbleweed rovers are small, spherical, autonomous rovers that use wind power rather than heavy internal battery sources to propel themselves around the surface. Harnessing natural sources cuts costs, meaning NASA could theoretically deploy a whole team of these rovers for the cost of one traditional wheeled rover.The three wheeled rovers NASA has sent to Mars – Sojourner, Spirit, and Opportunity – have all found the same thing: the planet is covered in rocks and sandy dunes. It's a challenging surface. In 2005, Opportunity got its wheels stuck in sand. It stayed there for over a month while engineers on Earth practiced getting out of a similar sand trap with the rover's Earthbound twin. In the end, rocking back and forth was the key to freeing the wheels.Troubleshooting these types of problems with tumbleweed rovers won't be so easy. Without a power source or any real way to steer it, a stuck tumbleweed will likely be left there. Sand traps aren't the only threat to these unconventional rovers; rocks will likely pose a bigger threat. That could be a real problem: the Martian surface is extremely rocky. On average, there is one significantly-sized rock every three feet on the Red Planet.In all likelihood, a tumbleweed rover's ability or inability to maneuver through rock fields will be the deciding factor for its use in a mission. If rocks are likely to hamper its reaching places of interest, which frequently lie in regions outside of suitable flat landing sites, NASA may stick with wheeled rovers since wheels offer clearance of ground hazards.But it doesn't look like rocks will be prohibitive for the tumbleweed rover. Providing the tumbling rovers are light enough and the right size – about 20 feet in diameter – and catch the Martian breeze just right, they could potentially roll over the rocks without getting stuck. Gravity will also be a big help in this matter, or Mars' much weaker gravity to be exact. Any wind-blown design is likely to bounce more than roll across the Martian surface, bumping along in one-third the gravity of Earth’s in an atmosphere is only one-hundredth the pressure that we experience at sea-level. In these conditions, a small motion would be enough to get the rolling rover airborne.Scientists have already started putting tumbleweed rovers through computer simulations, and they look like a fairly promising design. If theory translates to practice, NASA could opt to use these rovers on a mission and open the door for a whole new type of exploration. It could be that the first men on Mars travel around the surface in giant, wind propelled hamster balls.
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