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Geek Trivia: What inside joke is hidden in the wheels of the Mars Curiosity rover?

At least one design element of the Mars Curiosity rover--its wheels--combine function and whimsy, as they contain an inside joke.

As of this moment, the most advanced robotic planetary surface probe ever constructed by humankind is in the early stages of unraveling the untold mysteries of the Red Planet. The Mars Science Laboratory mission has reached its most momentous phase: successfully deploying the Curiosity rover onto the Martian surface.

And Curiosity is a serious piece of work.

First, there was Curiosity's landing, which involved ballistic reentry, a massive parachute, retrorockets, and a flying crane. Every system had to function in perfect sequence, after traveling millions of miles in the cold soak and radiation heat of interplanetary space, culminating in a dramatic, tension-fraught touchdown worthy of a Hollywood movie.

What that touchdown delivered was, without exaggeration, a nuclear-powered robot car equipped with a laser cannon. Seriously.

It all begins with Curiosity's power plant, a radioisotope thermoelectric generator (RTG). Satellites and space probes have used RTGs for decades, but no planetary rover has ever been equipped with one before. An RTG isn't a nuclear reactor, but a series of thermocouples wrapped around slugs of non-fissile Plutonium-238, which gives off stable amounts of heat that are converted into electricity (or redirected to keep rover systems from freezing). Because Curiosity uses an RTG rather than relying on solar power like previous Mars rovers, Curiosity can carry more instruments, and instruments that draw more power.

Like an infrared laser drill that vaporizes rock samples.

Every aspect of Curiosity is designed to maximize the amount of data relayed back to NASA scientists. Well, almost every aspect. At least one design element--Curiosity's wheels--combine function and whimsy, as they contain an inside joke.


Get the answer.

Curiosity's wheels are multifunction. Their primary use case--obviously--is locomotion. However, NASA uses visual evidence to estimate distances and scales on Mars, so Curiosity's wheel tracks are designed to aid in this effort. A series of irregular holes placed in each of Curiosity's six wheels create a repeating pattern as the rover drives across the Martian desert.

By observing the placement of these tracks, NASA scientists can confirm that the rover's odometers are working properly and use the visual evidence to judge distances in photo data that Curiosity sends home. But so long as you're punching holes in a rover's wheels to create an identifiable pattern, you may as well have some fun with it.

The aforementioned holes are placed in between the horizontal treads of the rover wheels, so the only variation engineers had was width of the holes between the treads--the height was fixed. Thus, the pattern is of long and short holes or, for you cryptography geeks, long and short data signals. There's a venerable if not always well-recognized encoding standard for long and short signals--Morse Code. Each wheel on Curiosity devotes three treads to the odometric encoding, which gave Curiosity's designers three letters to play with.

Every time Curiosity's wheels complete a revolution, they print the Morse Code for JPL on the Martian surface in honor of Caltech's Jet Propulsion Laboratory, which oversees the Mars Science Laboratory project.

That's not just some clever cryptographic Curiosity-encoding; it's an ingenious interplanetary instance of inside joke-worthy Geek Trivia.

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Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger -- amusing and abusing IT pros. Read his full profile. You can a...


The Darbs are slipping.... (Unless they aren't. If you slipped one on Curiosity, let us know.) --an interested Lloydie


I wonder which ham radio operator at JPL came up with the idea. bill WB8BVX


He told us that same story. It turns out that JPL does so much legwork for which they never get any credit. JPL wasn't allowed to logo anything or stamp any identifying marks from their shop. NASA is the big brother (translate - bully) and they don't like the spotlight to shine anywhere else. So when they were told that there needed to be this imprint put on the wheels to mark the sand, some joker came up with the idea to make that "identifiable mark" something that would poke big bully... er.... big BROTHER in the eye. Now I know the story is true! (I mean, if JAY says it...!) I am also surprised that it is still there. I was told this was done not for this mission, but for the FIRST rover!!!

Jay Garmon
Jay Garmon

...but since there are ACTUAL NASA ROCKET SCIENTISTS who occasionally read my stuff and comment (which is weird enough in itself), I'd await the judgment of the talkback community before taking my posts as unquestioned gospel.

Deadly Ernest
Deadly Ernest

The pattern was most probably set for the first Rover and the same mould used for each set of wheels since then as I'm fairly certain they're the same size etc.


The entire Sojourner rover was about the size of one of Curiosity's wheels. Beyond the size, they've redesigned the wheels with each generation of rover. Here's an image showing the 3 next to each other: Also, I think that RipVan might be misremembering some details in that story, because it doesn't sound right at all. First, Sojourner didn't have any visual odometry capabilities, so wouldn't have had a reason for a specific pattern in the wheels. Also, I've seen tons of pictures of Sojourner, and the only pattern I've seen has been the zig-zag of the cleats on it. It's possible that any morse code pattern on it was always against the ground in all photos, but that seems unlikely. Beyond that, I just don't buy the fact that JPL sees the rest of NASA as a bully. I only know one person that used to work at JPL, but he obviously has a great deal of respect for the entire NASA organization. And saying that NASA doesn't like the spotlight shining somewhere else is sort of ridiculous since JPL IS part of NASA. And, it's just not true that they're not allowed to logo anything. First, the website for every mission that's managed by JPL is hosted at JPL's website, and has their logo all over it. Yes, even Pathfinder/Sojourner had a website when it was launched (JPL still has a copy of the site up, if you want to be reminded how bad web design was in the mid-90s!). Also, the mission patches almost always have the JPL logo on them. Here's the one from Pathfinder: And finally, at least for Pathfinder/Sojourner (the first Rover), JPL's logo was actually on the launch vehicle!

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