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Solar-Powered Mars Rover Issues, Lessons From MER And Future Ideas
mcaplinger
post Aug 22 2014, 01:28 AM
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QUOTE (algorithm @ Aug 21 2014, 12:17 PM) *
Personally I wouldn't bolt on a nuclear generator just to enable a rover to last the lifetime of a wheel...

Without some kind of active solar panel cleaning, which we don't know how to do in a practical and flight-qualified way, there is simply no way to guarantee even two years of mission life on Mars without an RTG. The MERs got lucky with cleaning events.

MSL was designed to last two years, which means in general that it was life-tested for four years. Anything past that is gravy.

That said, it's been stated that the degree of wheel damage was unexpected. Hindsight is 20/20.


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Don1
post Aug 22 2014, 01:48 AM
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QUOTE (mcaplinger @ Aug 21 2014, 05:28 PM) *
Without some kind of active solar panel cleaning...


Couldn't a blast of gas be used to clean solar panels? Something like the air in a can used to clean circuit boards?

We may be two years into the MSL mission, but we are still a long ways from the clay rich regions of Mt Sharp which were the original target. I think Curiosity needs to get at least that far to be seen as fully successful.
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Phil Stooke
post Aug 22 2014, 01:57 AM
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Sure, but then you need the pump or compressor or whatever mechanism is driving that blast, plus the ducts to distribute it, and enough power... getting complex and massive already.

Phil


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Vultur
post Aug 27 2014, 03:47 AM
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QUOTE (mcaplinger @ Aug 22 2014, 01:28 AM) *
Without some kind of active solar panel cleaning, which we don't know how to do in a practical and flight-qualified way, there is simply no way to guarantee even two years of mission life on Mars without an RTG. The MERs got lucky with cleaning events.


This is something I'd kind of wondered about... given that Spirit lasted dozens of times past the 90 day lifetime and Oppy is still going, in different locations, doesn't that move a bit beyond "got lucky" and into "Mars is a more benign environment for solar panels than previously assumed"?
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mcaplinger
post Aug 27 2014, 01:13 PM
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QUOTE (Vultur @ Aug 26 2014, 08:47 PM) *
...move a bit beyond "got lucky" and into "Mars is a more benign environment for solar panels than previously assumed"?

There have been no cleaning events at Gale as far as I know. I think that if a MER had landed at Gale it would be dead or dying from power loss by now.

Also, there hasn't been a global dust storm since 2001, but if there had been, there's an excellent chance that the MERs would not have survived it.


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RoverDriver
post Aug 27 2014, 09:12 PM
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Mike, we had a global storm in the Summer of 2007 and both MERs survived it. I thin tau went up to 5 and beyond.

Paolo


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serpens
post Aug 27 2014, 11:06 PM
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But it was indeed a close run thing.
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mcaplinger
post Aug 28 2014, 01:17 AM
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QUOTE (RoverDriver @ Aug 27 2014, 02:12 PM) *
Mike, we had a global storm in the Summer of 2007 and both MERs survived it.

You're right, though we could have a discussion about the definition of a global dust storm versus a planet-encircling dust event, etc. At any rate the 2001 storm was much more severe than the 2007 one and current thinking is that these are somewhat random and hard to forecast. I think that the 2001 storm would have killed the MERs almost certainly.

It's an interesting question as to how long a solar-powered lander would be claimed to last at this point and whether MER experience could be used to lengthen that beyond a few months. I'm skeptical that the MER experience could be banked on.

[This discussion is off-topic for this thread but I think there's some new and interesting points being made, so perhaps the mods could move these items elsewhere if they wish.]


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nprev
post Aug 28 2014, 04:23 AM
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Since this topic periodically recurs, this thread is for discussion of same. Note that there are many posts related to this topic on many threads, but no attempt will be made to consolidate them here save for the most recent (Aug 2014).


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RoverDriver
post Aug 29 2014, 01:06 PM
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Mike, I "landed" on Mars only in 2004, so I don't know the details of the 2001 storm, and am glad I didn't have to deal with that one! I think both Gusev and Meridiani had a tau around 5 during 2007 storm and I don't think we would have survived if the event lasted months at that level of energy and it is extremely unlikely we would have survived if that had happened during (Martian) Winter. The data collected over the past 10 years seem to indicate that these events are more likely during the Summer tho.

And for sure you cannot do statistics on only two data points, although many do it every day. ;-)

My beef with MSL RTG is that precludes vision in the back...

Paolo


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rlorenz
post Nov 28 2014, 01:29 PM
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QUOTE (mcaplinger @ Aug 27 2014, 08:13 AM) *
There have been no cleaning events at Gale as far as I know. I think that if a MER had landed at Gale it would be dead or dying from power loss by now.


Yes. It seems the clearing events may be intensive convective vortices (which when rendered visible by lofted dust, are dust devils).
A recent paper (https://www.lpl.arizona.edu/~rlorenz/clearingevents.pdf) shows that not only do Spirit clearing events correlate in time with the
observed dust devils, but the frequency of Pathfinder and Phoenix pressure drops recorded by meteorology instrumentation, when extrapolated
to the laboratory dust-lifting threshold, correspond to the frequency of clearing events (one per 100-700 days). Too bad MER didn't have even
a pressure sensor...

The meteorological setting of Gale appears to suppress the boundary layer convection to a large extent - while small pressure drops have been recorded,
only one visible dust devil has been detected AFAIK.

So, a solar powered lander might be well-advised to land where you see dust devil tracks... (which is the case for InSight, btw) that way you know
panel-clearing should occur.
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James Sorenson
post Nov 28 2014, 08:06 PM
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An appropriate topic I guess for posting these animated GIF's of Curiosity's sundial that I made less than a week ago.

M34
https://www.flickr.com/photos/43581439@N08/...104451/sizes/o/
M100
https://www.flickr.com/photos/43581439@N08/...363216/sizes/o/
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