Curious Rover Tracks at Space Expo 2014

This week I enjoyed visiting the Space Expo 2014 "The Great Challenge of NASA/JAXA" which is being held 19 July to 23 September at Makuhari Messe (幕張メッセ) in Chiba, Japan.

1/10 size Saturn V model at Space Expo 2014

Space Expo 2014 exhibit floor, with hanging ISS model

Lunokhod ("Moonwalker") model

Curiosity Rover model at Space Expo 2014

Some of the most fun things were the life size models of the Space Shuttle nose section (including toilet) and the Japanese International Space Station (ISS) module - the Japanese Experiment Module (JEM, or Kibo, きぼう, meaning hope). This included the astronaut's entrance with its blue welcome curtain on the "ceiling" and small blue welcome message on the "floor", reading "Welcome to Kibo - please enjoy and relax in this brand new, spacious and the most quietest room in the ISS" (sic; see this guide to the ISS).

Life size Space Shuttle model's flight deck

Life size JEM/Kibo ISS module model with its "veranda"

I was pleasantly surprised to see an exhibit about Felix Baumgartner's Red Bull Stratos jump (lots of photos and Japanese text about this exhibit here). I remember watching this world record breaking sky dive on the internet.

Many of the models and artefacts had a brief English caption, but most of the text was of course in Japanese. Unfortunately for me that meant I could only look at the pictures and models for the Japanese rocketry history and JAXA space missions like Hayabusa which brought back comet dust (with its ion drive).

I found lots of interesting exhibits, but something which caught my eye in particular was the NASA Curiosity Mars Rover model - because one of the interesting design features was wrong...

Curiosity Rover model at Space Expo 2014

There are two things wrong with this, first and most obviously the tracks in the sand are wider than this model rover's wheels, although the zig-zag pattern looks consistent. Maybe the diorama setting was intended for an even bigger model?

Curiosity Rover model wheel and track mismatch

Second, the rover's wheel treads are not uniform - all six wheels bear a pattern (dot dash dash dash; dot dash dash dot; dot dash dot dot) which spells out "JPL" in morse code in the tracks (see this Scientific American article, or this NASA page). This is partly a homage to short for NASA's Jet Propulsion Laboratory in Pasadena, but also has a practical application in helping determine the distance travelled (or amount of wheel slip) by analysis of images of the tracks.

The older Soviet rovers like the Lunokhod shown earlier used a free wheel odometer approach (there was not enough light at the back of the model to photograph the spiked ninth wheel), combined with analysis of ariel photos. This had put the off-Earth rover record at 37.5km but a revised estimate using more accurate imagery put the Lunikhod 2 lunar journey at 42km, which at the time of writing has yet to be beaten.

XCKD Spirit Mars Rover cartoon

I wondered what the Sarcastic Rover (@SarcasticRover) would have as morse code on its wheels? With the XCKD Spirit Mars Rover cartoon in mind, I guessed SOS - and I was close ;)

SarcasticRover (@SarcasticRover) August 9, 2012:
Little known fact: The treads on my tires write JPL in morse-code...
all except one, which writes "SOS WTF BRB"!
twitpic.com/ahearg