What I love about JPL, is the accidental discoveries. When one of their positioning devices failed to work as expected, they had a bit of a problem.. They couldn’t measure how far the rover had traveled. What the heck could they do now? It’s not like they could send the rover out to get a tape measure!
Then someone look at the mockup of the rover, which they were using to try to figure out a solution, and they pointed to the wheel, where the bolt holes were in the tread that held the rover to it’s delivery system. “Can’t we just measure that?”
Every couple of feet, the rover makes a very distinctive diamond shape on the dust of Mars. The bolt hole in the metal ‘tire’ that is on the Mars rover Spirit and Opportunity was the perfect measuring device, and they had all the pictures they needed to measure not only the exact distance that the rovers traveled, but also a standard comparison - a ruler, if you will, for measuring anything with the rover’s cameras.
So when Curiosity was being planned, they scrapped the existing ‘unmarred’ tires and instead placed a mark in the tread, so that they could use the footprint of Curiosity to make measurements. And being geeks, they didn’t just put in an unnecessary bolt hole, but instead, three lines of dots and bars - Where ever Curiosity goes on Mars, it leaves a Morris Code footprint stating ‘JPL’.
Great story! I love it ... geekery is so cool!