In the humid, foggy coastal plains of South America there is a herb that survives without roots. It is constantly moving and due to its spherical shape is easily carried by the wind and absorbs moisture from the early morning dew, capturing it in its thin little branches. During their lifetimes, these rolling bushes cover vast distances helped by the wind.
Named after this herb (and its American relatives) is the latest generation of research robots that scientists at the "Jet Propulsion Laboratories" in Pasadena/California are working on with the aim of sending them on the journey to the Red Planet on the proposed Mars exploration mission in 2009.
The idea is just as natural as it is genial: why take excess weight in the form of expensive propulsion systems and fuel on board a robot, when you can do without? In addition, "Tumbleweed" has its own airbag when it comes to severe impacts (like on landing) and collisions with cliffs.
The first tests in Greenland and the Antarctic were a complete success. "Tumbleweed" is (for the mission on Mars) a plastic inflatable ball up to six metres high that weighs around ten kilos. Only with the help of the wind should it accomplish inclines of up to 25 percent. On the outside it is equipped with sensors and on the inside carries a protected fibreglass tube containing measuring devices (diagram).
In Greenland the unusual research sphere covered a stretch of 100 kilometres independently using only wind power and thereby delivered current information on temperature, humidity and air pressure changes, deep scan radar and magnetic field data as well as a ground profile all via radio antenna.
Robot expert and project leader Dr. Alberto Behar from NASA/JPL: "It is a very easy way of collecting important data in extreme and life threatening environments. On Mars, where powerful winds prevail, you could use this invention to explore both poles and draw important conclusions for Earth from the comparatively simple climate system of the red planet. We have just launched a second Earth mission, where our ball will undertake a 2000 kilometre long journey in the Antarctic, from the South Pole out to the coast. We still have very little information about this region because of the severe measuring conditions."
But tumbleweed can do more than just roll with the wind through the region and silently measure all that lies before it. Dr. Alberto Behar: "We have taught Tumbleweed two unusual tricks that strongly broaden its area of use. On command it can release gas so that it becomes flat on one particular side and stays still despite any wind, meaning it can also take ground samples at interesting places. Then it inflates once again and rolls further. The second idea that we are currently testing are small weights inside, which can move around so as to allow the ball to turn on a specific axle when rolling. In this way a camera with a motor can be mounted to the fibreglass axis that counterbalances the movement and takes photographs of the surroundings."
Even including times when no wind blows, Tumbleweed can reach a speed of 1.3 km/h in unknown terrain. On the contrary, the otherwise very successful Mars-Rovers "Spirit" and "Opportunity" are slow coaches with their 0.05 km/h.