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Mars Winds Clean Spirit's Solar Panels Again
Titoxd writes "In a blast from the past, NASA reports that Spirit's solar panels have received a much-needed cleaning courtesy of the Red Planet. The report states, 'The cleaning boosts Spirit's daily energy supply by about 30 watt-hours, to about 240 watt-hours from 210 watt-hours. The rover uses about 180 watt-hours per day for basic survival and communications, so this increase roughly doubles the amount of discretionary power for activities such as driving and using instruments.'"
Cruise is something of an exaggeration... they've gone 13 miles in 5 years, put together. The Lunar Rover missions each went longer than both combined in 3-4 hours, at top speed they'd pass the rovers within the first hour. Semi-stationary crawlers is a more accurate description, but of course they've been loaded up with scientific equipment rather than for showing off.
Live today, because you never know what tomorrow brings
So what about an air cannon or something? Small pump to take in Martian air, build up pressure, and a small nozzle directed at the panel to blow the dust off.
I know, every ounce of weight and every bit of energy has to be calculated and accounted for. But they had to know that dust would accumulate on the panels and should have accounted for that with some type of design.
90 days.
They did know. They also knew that all the possible solutions had significant costs and/or chance of failure. (As far as the air cannon, Mars air is very thin, so you have to have a quite significant wind to move the dust.)
Arthur C Clarke wrote a nifty short story that encapsulated some of this. I can't even remember the title, so spoilers are uselss, and I'll just give the gist.
Two astronauts were exploring on the moon, and the wandered into a dust bowl. They got a little dust on their faceplates, and made the mistake of wiping them. The generated static transferred all of the dust to the faceplate, and they were still deep enough in the dust that it attracted more. So even though the dust bowl is shallow enough to simply walk out, they can't see, and so far they haven't found anything they could rub the faceplate with where the static electricity would go the other way, taking the dust off.
Solution:
They rubbed faceplates together. One faceplate takes the charge that takes the dust, the other cleans. Then the astronaut with the clean faceplate can see the way to the buggy, leading the other.
The living have better things to do than to continue hating the dead.
They never expected the mission to go this long. Things were calculated at a success level of 90 days.
Indeed because of the success of these two rovers the next missions will be similar. The next mission may or may not benefit as often it is the failures that teach better than the successes.
It may be that the rover happened to have landed in a particularly windy part of the planet, or a part with a particularly un-clingy(love my technical wording!) local dust conditions and the next mission may be different and fail even if the exact same equipment is used.
Exactly. "Designed to last 90 days" presumably means something like "Designed to have a 95% chance of lasting 90 days". Which probably means it has a 90% chance of lasting 180 days, an 80% chance of lasting 360 days...
I don't know what confidence threshold NASA uses, maybe more than 95%. So the 5 years these lasted is lucky, but not so completely off the charts as it might seem.
Anyone interested in the Mars Exploration Rovers' mission should check out Mars And Me, the unofficial diary of a Mars rover driver. Scott Maxwell is blogging his daily work at JPL exactly five years later. A very interesting and well-written look at the day-to-day operations of a truly amazing scientific expedition.
Actually, it's pretty easy. We've discussed this before every time the subject comes up. Put a continuous roll of clear plastic at one end of the panel and a take-up roll on the other end. Make the plastic travel in a track with brush seals so that nothing can easily get in behind the plastic. Periodically roll the plastic to keep the portion atop the panel clear. When you get to the end of the roll, reverse the direction. You'll have less power that pass, and eventually this won't be practical, but it will work for a really long time. For that matter, you could have a series of brushes along the path of the plastic beyond the panels that would significantly reduce the dust level on the plastic even on the second and subsequent passes. And because it is just a simple motor on a spool, it is about as mechanically trivial as you can get, unlike... say a windshield wiper... and best of all, if you scar the plastic, you're not scarring the panel itself and risking causing a panel failure.
Check out my sci-fi/humor trilogy at PatriotsBooks.