Rover Leaves Tracks in Morse Code
A Morse code pattern imprinted in the track marks of NASA's Curiosity will help the rover drive more accurately.
NASA's  Curiosity rover took its first test stroll Wednesday Aug. 22, 2012, and beamed  back pictures of its accomplishment in the form of track marks in the Martian  soil. Careful inspection of the tracks reveals a unique, repeating pattern,  which the rover can use as a visual reference to drive more accurately in barren  terrain. The pattern is Morse code for JPL, the abbreviation for NASA's Jet  Propulsion Laboratory in Pasadena, Calif., where the rover was designed and  built, and the mission is managed."The  purpose of the pattern is to create features in the terrain that can be used to  visually measure the precise distance between drives," said Matt Heverly,  the lead rover driver for Curiosity at JPL.This driving  tool, called visual odometry, allows the rover to use images of landscape features  to determine if it has traveled as far as predicted, or if its wheels have  slipped. For example, when the rover drives on high slopes or across loose soil,  it will routinely stop to check its progress. By measuring its distance  relative to dozens of prominent features like pebbles or shadows on rocks -- or  patterns in its tracks -- the rover can check how much its wheels may have  slipped. If Curiosity has not slipped too much, it can then re-plan the next leg  of its drive, taking its actual position into account."Visual  odometry will enable Curiosity to drive more accurately even in high-slip  terrains, aiding its science mission by reaching interesting targets in fewer  sols, running slip checks to stop before getting too stuck, and enabling precise  driving," said rover driver Mark Maimone, who led the development of the  rover's autonomous driving software.The  Morse code imprinted on all six wheels will be particularly handy when the  terrain is barren. Curiosity won't be able to read the Morse code symbols in  the track marks directly, but it will note that the pattern is a high-contrast  feature. This will give the rover the anchor it needs in an otherwise  featureless terrain."Imagine  standing in front of a picket fence, and then closing your eyes and shifting to  the side. When you open your eyes, you wouldn't be able to tell how many pickets  you passed. If you had one picket that was a different shape though, you  could always use that picket as your reference," said Heverly. "With Curiosity,  it's a similar problem in featureless terrain like sand dunes. The hole  pattern in the wheels gives us one 'big picket' to look at."NASA's  Mars Exploration rovers Spirit and Opportunity also used visual odometry to  ensure accurate driving in difficult terrains. Their wheels had been bolted to  their landing platform, leaving holes that left distinguishing marks in their  tracks. Those marks proved critical for the visual odometry system on Opportunity  when it traversed the relatively featureless terrain at Meridian Planum.  Opportunity is still trekking on Mars more than eight years after setting down  on the Red Planet.Curiosity  likewise has holes in its wheels, only in the shape of Morse code letters."Even  though Curiosity didn't need to be bolted down, we wanted to have the holes  anyway. The mechanical team suggested multiple smaller holes rather than one  large one like the Mars Exploration Rovers had, and one earlier design had  spelled out letters in a cleat pattern, so I proposed using a Morse code version,"  said Maimone. "And the rest is history."JPL  manages the Mars Science Laboratory/Curiosity for NASA's Science Mission  Directorate in Washington. The rover was designed, developed and assembled at  JPL, a division of the California Institute of Technology in Pasadena.More  information about Curiosity is online at:http://www.jpl.nasa.gov/msl,http://www.nasa.gov/mslandhttp://mars.jpl.nasa.gov/msl.Follow  the mission on Facebook at:http://www.facebook.com/marscuriosityand on Twitter at:http://www.twitter.com/marscuriosity.