Curiosity leads on new paths
Nasa's latest Martian explorer Curiosity has been quite the headline catcher recently.
First there was its novel and daring descent through the Martian atmosphere. A few days later there was its first panoramic picture of from Gale Crater (and there was Mohawk Guy, of course, who almost stole the whole show). But Curiosity is not there to just take pictures. It has to start moving. Sounds simple enough, but for Curiosity, stranded millions of kilometres from its human operators, moving about safely is far from simple.
Curiosity is the size of a car, with a long-lasting radioactive power source, a rock-vaporising laser, a fully articulated arm and numerous scientific instruments to test for water and the organic chemicals that make up life as we know it. But before it can analyse any samples it has to reach them, and to do that it relies on some very futuristic technology.
On the mechanical side Curiosity's mobility comes from its six wheels, each driven by an independent electric motor. The wheels are mounted on a so-called rocker bogie suspension that evens out the ride for the rover as it travels over rough terrain. It can tilt 45 degrees in any direction without tipping. Each of the front and rear wheels also has its own steering motor which, among other things, allows it to turn 360 degrees on the spot.
Curiosity's handling may be out of this world but its top speed of less than one kilometre per hour would leave a terrestrial traveller cold. But Curiosity is only expected to drive up to 20 kilometres during its primary mission, and has at least 23 months to do it. Which is good, since driving on Mars comes with an additional complication.
Because radio waves take several minutes to travel between here and Mars it's not possible to drive the rover like an oversized remote-control car. By the time commands from earth reach Mars and feedback from the rover returns to earth half an hour or more may have elapsed: plenty of time for Curiosity to have fallen off a cliff operators on earth haven't yet seen.
To prevent such a catastrophe Curiosity has some intelligence built into it. It is equipped with several pairs of stereo cameras which give it a comprehensive view of its surroundings, with depth perception. Earthbound operators use these to plan Curiosity's next move, and Curiosity uses them to measure its progress against the plan and to avoid known obstacles. When it encounters something unexpected the rover can often take evasive action on its own, or it can stop and wait for fresh instructions.
Curiosity is an engineering marvel but it is this software that gives the rover the autonomy it needs to become a practical planetary explorer. Perhaps humans will eventually be doing the driving on Mars, but by the time we make that giant leap machines might be doing all the driving anyway - even back here on earth.