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
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.