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Mars Science Lab Cameras
djellison
post Nov 8 2008, 09:31 PM
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QUOTE (mcaplinger @ Nov 8 2008, 08:08 PM) *
I had thought the dust buildup was mostly on the hazcams, which are much closer to the ground.


Spirit's cameras all remain in great health

Opportunity got a smattering in both Navcams and Pancam's. If you notice a lot of Pancam imaging with Opportunity is done with only one half, or 3/4s of the CCD, as one side got quite a smattering.

http://marsrovers.jpl.nasa.gov/gallery/all...nity_p1671.html is an example of the technique.

http://marsrovers.jpl.nasa.gov/gallery/all...CSP2629L4M1.JPG is a typical example of the obstruction


Doug
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mhoward
post Nov 8 2008, 09:46 PM
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QUOTE (djellison @ Nov 8 2008, 02:31 PM) *
Opportunity got a smattering in both Navcams and Pancam's.


The contamination happened during the dust storm, didn't it? So it's not exactly 'buildup' so much as a 'smattering' as you put it.

Regardless, the contamination of Opportunity's optics remains distressing - I'm sure to the science team as well as the sightseers.
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mcaplinger
post Nov 8 2008, 11:34 PM
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QUOTE (mhoward @ Nov 8 2008, 01:46 PM) *
Regardless, the contamination of Opportunity's optics remains distressing...

http://www.planetary.org/news/2007/0930_Ma...ate_Spirit.html

It looks like the effects of this contamination could easily be taken out with a proper flat field, and I'm a little surprised that they haven't done this.

That said, owing to the configuration of the Mastcam I think it will be far more resilient to this sort of problem.

There was never any serious consideration given to adding a cover mechanism to the Mastcam, and nothing I see in the Pancam data would justify the added cost, complexity, and risk. I wouldn't even know how to begin to implement a "wiper" that would work reliably under martian conditions, and some kind of roll of clear material that could be driven past the lens would be problematic for all kinds of reasons.


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ugordan
post Nov 9 2008, 09:40 PM
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QUOTE (mcaplinger @ Nov 9 2008, 12:34 AM) *
http://www.planetary.org/news/2007/0930_Ma...ate_Spirit.html

It looks like the effects of this contamination could easily be taken out with a proper flat field, and I'm a little surprised that they haven't done this.

If you look closely at the comparison mosaic on that page, notice that while the corner darkening was removed with a new flatfield, the frames suffer from lowered contrast there. The dust particles are no longer just a nuisance in the way, they diffuse/diffract the light. The effect can be likened to Titan's haze but on a much different scale. A flatfield simply cannot remove that. Had the dust been deposited on the actual CCD the situation would probably have been different.


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elakdawalla
post Nov 9 2008, 10:20 PM
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QUOTE (mcaplinger @ Nov 8 2008, 12:39 PM) *
The cameras are normally stowed pointing down. Was there some period on MER when they were left pointing up?

This is a question I've been wondering about too. Were the cameras left unstowed at some point, or did Oppy just happen to get smacked in the face with an unusually large pile of dust during the brief period when it was trying to do imaging one day?

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mcaplinger
post Nov 10 2008, 01:05 AM
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QUOTE (ugordan @ Nov 9 2008, 01:40 PM) *
A flatfield simply cannot remove that.

If by "flat field" you mean something that merely multiplies each pixel by a single number, I agree. But these sorts of stray/scattered light problems can be addressed with more sophisticated techniques, for example the way the NEAR images were recovered after the front elements were covered with monoprop burn products. See "Inflight Calibration of the NEAR Multispectral Imager II. Results from Eros Approach and Orbit" by Murchie et al in Icarus 155, 1. I'm not sure the MER images are bad enough to require that level of processing though.


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Deimos
post Nov 10 2008, 01:53 AM
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QUOTE (elakdawalla @ Nov 9 2008, 10:20 PM) *
This is a question I've been wondering about too. Were the cameras left unstowed at some point...

First, a 'stowed' camera is still at risk on MER. There are no in-flight dust shields for Navcam, Pancam. Looking down avoids sedimentation of dust, but not turbulence. I think turbulence maybe was involved. Second, I don't think the camera bar has been left stowed at nadir in quite some time. Stowing the cameras now places them looking sorta down, sorta out, I think. The actuators were not designed for a 5 year mission, let alone one with Opportunity's current ambition. If they fail, they should fail where Navcam is still useful rather than contemplating the rover's navel, umm, deck.
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DDAVIS
post Nov 10 2008, 09:07 PM
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I wouldn't even know how to begin to implement a "wiper" that would work reliably under martian conditions...

I recall reading that Viking had two methods to avoid dusty optics, a physical barrier which covered the 'slit' when the camera was in its 'rest' position as well as compressed air which could be used to blow off the optics. I would think the latter could be adapted to a wide variety of camera designs.

Don
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Phil Stooke
post Nov 10 2008, 10:41 PM
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"I would think the latter could be adapted to a wide variety of camera designs."

I think we need it for Spirit's solar panels now...

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mcaplinger
post Nov 10 2008, 10:59 PM
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QUOTE (DDAVIS @ Nov 10 2008, 01:07 PM) *
I would think the latter could be adapted to a wide variety of camera designs.

I'd be willing to bet that the tank to contain the gas would weigh more than an entire Mastcam camera head. Not really practical given the mass constraints.


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DDAVIS
post Nov 11 2008, 12:18 AM
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the tank to contain the gas would weigh more than...

Perhaps, but I wonder what the Viking unit weighed? How much more compact cound a similar modern system be built? I imagine something like a soda charger cylinder filled with very clean compressed gas, perhaps giving puff(s) of gas upon demand. A magnetic 'ring' around the lens could also help. However this is dealt with, cameras for long term Mars surface missions will require more attention to the dust hazard as part of the design.


Don
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djellison
post Nov 11 2008, 12:28 AM
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QUOTE (DDAVIS @ Nov 11 2008, 12:18 AM) *
A magnetic 'ring' around the lens could also help.


Now that's a solution I've not seen mentioned before, and it might make a lot of sense.
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Fran Ontanaya
post Nov 11 2008, 12:34 AM
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What about holding the air in the bodywork itself? unsure.gif




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djellison
post Nov 11 2008, 08:27 AM
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Making the entire electronics box a pressurised body? Given that it has to travel thru a vaccum? How do you engineer in the insruments and their openings to the sample collection mechanisms. That's an epic engineering challenge right there.
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AndyG
post Nov 11 2008, 10:33 AM
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For Mars the body wouldn't have to be at insane levels of pressure - just "enough" over the external ~1 kPa to provide a squirt of gas where and when you need it. I don't think the high pressure 20 MPa sort of structure you see on air tanks is at all necessary here.

Just to put this into perspective: the r/c model sub community regularly work with pressures up to ~50kPa and manage with commercial linkages/prop shafts, etc., penetrating the core electronics box without too many problems.

That said, this Giotto air puffer would seem to be a more practical solution. And it's even rocket-shaped!

Andy
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