QUOTE (Steve Squyres)
And in the "it's always something" department... we are now facing a new threat to both vehicles. It is dust storm season on Mars. Dust storm season happens once per martian year, during the southern summer when the input of solar energy into the martian atmosphere is highest. And southern summer is now upon us. The atmospheric dust levels at both of our landing sites are high and climbing, and in fact the dust level at the Opportunity site is the highest we've ever encountered. It's not a serious threat yet, but it's a worry, and we're watching the dust levels in the atmosphere very closely.
The thing to realize about dust storms is that the threat is not high winds, nor is the primary threat dust buildup on the solar arrays. Instead, the primary threat is simply the attenuation of sunlight by dust that is suspended very high in the atmosphere, and the resultant loss of power from our solar arrays. RIght now we've got power to spare on both vehicles, and there is no imminent danger. But martian dust storms are notoriously hard to predict. In some years things are pretty quiet, and in other years what starts out as a small regional storm can blow up quickly into a monster that covers the whole planet, with solar attenuation that could be very bad for our vehicles. We have no way of knowing what's going to happen this year.
The thing to realize about dust storms is that the threat is not high winds, nor is the primary threat dust buildup on the solar arrays. Instead, the primary threat is simply the attenuation of sunlight by dust that is suspended very high in the atmosphere, and the resultant loss of power from our solar arrays. RIght now we've got power to spare on both vehicles, and there is no imminent danger. But martian dust storms are notoriously hard to predict. In some years things are pretty quiet, and in other years what starts out as a small regional storm can blow up quickly into a monster that covers the whole planet, with solar attenuation that could be very bad for our vehicles. We have no way of knowing what's going to happen this year.
I think a thread about the possible effects is in order...
This page has some good info of the dust storm seasons. The peak season this year runs from July 01, 2005 (241° Ls) to August 16, 2005 (270° Ls). The good news is big bad 'global' storms are very rare so hopfully they won't be a problem anyway. (fingers crossed)
Steve mentioned that it is the loss of solar power due to the high levels of dust in the atmosphere that is the problem. I searched around for more info about how bad it could get and found this with regard to Sojourner:
QUOTE
a) Available panel power, any time during a clear-day (tau = 0.5) 6 hour period (20° N, untilted) exceeds ~11 W ( ~14.9 W at mid-day). This power could be attenuated by approximately a factor of two during severe dust storms (optical depth ~4, the worst that Viking experienced).
A factor of two loss of power wouldn't be good but that shouldn't be much worse than what Spriit had before her cleaning event, so should be survivable.
I think we'll have to be very unlucky to loose either rover to dust storms in the near future. I hope I'm right!
James
