The Tumbleweed rover is a concept for a long-range wind powered robot that could someday roam the polar ice caps of Mars or other planets. NASA engineers first came across the idea when chasing down an oversized spherical wheel from a conventional rover that broke off and blew away in the wind. They noticed how little wind was required to propel the wheel and how rugged it seemed. In 2001, JPL engineers developed the preliminary design for a spherical wind-powered rover. About the size of a beach ball, the rover did not perform as well as hoped. After many revisions, NASA arrived at a final scaled design which passed initial testing in Antarctica.  Researchers deployed a single two meter Tumbleweed rover model for eight days in January 2004.  The 40 kilogram spherical rover reached speeds of 30 kilometers an hour as it rolled across the icy plane.

Inside the Mylar ball is a long shaft extending the diameter of the sphere.  All of the rover's electronics are embedded in this shaft, including electronics to measure temperature, humidity, and air pressure. The Tumbleweed prototype communicates with scientists via GPS, however future versions designed for Mars would correspond with satellites in place over the planet. Future versions of the rover might also include an onboard camera that peeks out from the end of the instrumentation axle, as well as sensors appropriate for missions of discovery such as magnetometers and water-seeking radar. In order to control the direction of the rover, the internal shaft can change length using pneumatics controlled by onboard software. Making the spherical rover slightly oblong persuades the rover to move in a straight path.  When the rover reaches a destination of interest, an internal air pump deflates the rover just enough to keep it grounded. The rover maintains an optimum internal temperature by re-circulating heat generated by its electronics in order to maximize efficiency. This technique kept the rover at 52 degrees Celsius above the external temperature during its test in the Antarctic.

While other robotic missions designed for Mars and other planets involve complex egress and landing procedures, the Tumbleweed rover might be able to act as its own entry device, parachute, and airbag.  NASA intends to make the final eight meter version capable of surviving a 30 meter per second landing, similar to the airbags successfully utilized in the Mars Exploration Rover missions as well as the Pathfinder mission.