Window cleaning, Martian-style.

[edcrater]

In January 2004, Spirit and Opportunity departed their protective boxes and sallied forth onto the Martian surface. Consider the Pancam, and how the lenses stay clean.

{{{Mod: If this topic is old and chewed before, apologies and please cut.}}}

http://hobbiton.thisside.net/rovermanual/
4.3 Pancam optics
Both pancam cameras share identical optics. Camera optics are made up of 3-element symmetrical lenses, which possess an effective focal length of 38mm, and a focal ratio of f/20, yielding an IFOV of 0.28 mrad/pixel, and a square FOV of 16.8 degrees by 16.8 degrees per eye. A sapphire window covers the front of the pancam camera optics barrel, protecting the optics and filters within.The pancam is able to maintain focus from 1.5m to infinity. Defocus blur occurs at shorter ranges. At a range of 80cm, a defocus blur of approximately 10 pixels is experienced. (my bold)

There is plenty of info on the net on sapphire windows, and mostly it is to do with how clear, hard, scratchproof and "abrasion-resistant" they are, but I can find nothing about "self-cleaning".

There are oodles of technical camera stuff here:
http://www.news.cornell.edu/Chronicle/0 ... ancam.html
but nothing so prosaic as keeping the 'window' clean. It's all about how high-definition it all is, which would doubtless all come to naught if the sapphire window was dirty.

http://pancam.astro.cornell.edu/pancam_ ... about.html
has more stuff ditto, nothing about 'window' cleaning, but also has an amazing image as background to the data. It is clearly Earth as there is some artificial debris lower-right, but the rock formation is fascinating.

A search of many similar pages and sites for anything on keeping the sapphire window clean has drawn a blank. There is everything but. I find it fascinating that such an elementary idea as "window dirty, lens can't see, Rover can't perform" isn't discussed or even addressed anywhere. Surely, "mission-critical"?

The rovers were predicted to function for 3 months, though whether that was because of:
a. solar panel constraints
b. camera lens constraints or
c. some other factor,
...............I do not know.

Anyway, the cameras have functioned for nearly 5 YEARS!, sending back pictures as good as the day they started.

Now this is a very clever thing. Imagine, their camera on a stalk above a contraption, rolling across an alien landscape, battered by dust-devils and swamped by raging dust storms, and 4.8 years later, the sapphire windows covering the camera lenses are as clean as when they started.

I wonder whether the sapphire windows just stayed clean on their own by some form of high-technology, (coatings? something electrical? powered window cap? vibration?) or whether the Repeating Miraculous Electrostatic Cleaning that cleaned the panels (and which mainly occurred whilst on craters' edges) did it for them. And if it did, it was remarkably foresighted of nasa to know that it would do so, and enable them to omit any form of window-cleaning gadgetry.