Mars Rover Spirit Reaches Winter Tilt 88
An anonymous reader writes "The Mars rover Spirit has been inching carefully down the north slope of the feature 'Home Plate' to tilt its solar panels into the sun to survive the long Martian winter. On Friday, it reached a tilt of 29.9 degrees, probably the final tilt it will reach for the winter. Although it's used the tilt strategy to increase power over the Martian winter twice before, this year it's especially critical, since a global dust storm last summer has left the solar-powered rover covered with dust and starved for power. Geoffrey Landis, one of the MER scientists, commemorated Spirit's trek to the winter haven with a sonnet on his blog. (The second of the two rovers, Opportunity, is at a landing site that's not as far into the southern hemisphere, and hence has less need to find a tilted surface.) OSU has a website explaining some of the software used to visualize the terrain to optimize the tilt, and for the latest news, the ongoing log of the rover status is updated weekly."
Re:Stupid but obvious (Score:2, Informative)
Obviously, they were over-engineered because the environment on Mars was not known very well at design time.
If it had been known very well there would have been no point in sending them.
What I want to know is why the dust can't be shaken loose by rocking either the solar panel or the whole rover.
Re:Stupid but obvious (Score:3, Informative)
They have already been working on a few ideas [nasa.gov] in the labs.
Re:Stupid but obvious (Score:4, Informative)
Re:Stupid but obvious (Score:3, Informative)
Dust removal, hard but possible (Score:5, Informative)
With that said, let me note that dust removal is probably a bit harder than you realize. The optical data showed that suspended dust is extremely fine-- the cross-section weighted average particle radius is about 2.5 microns, so these particles are about the size of the particles in tobacco smoke. Particles this fine are predicted to adhere extremely well, by van der Waals and electrostatic forces. Picture trying to use your windshield wipers to clean the dust off your windshield, without using the wiper fluid. (and wiper fluid is tricky on Mars, too; you need it to stay liquid for long enough to run the wiper, and neither evaporate or freeze before it hits the panel). And blowing dust off is very tricky-- the atmospheric pressure is less than 1% that of Earth's. We could carry fluid, or compressed gas, but those would be consumables-- and if we had designed the mission and budgeted consumables for a 90 sol lifetime, we'd have run out of them years ago anyway, so we'd be in the same position we're in now anyway.
A feather duster might work, but feathers almost certainly violate the planetary protection policy :)
not obvious, but possibly stupid (Score:5, Informative)
What are the triboelectric properties of ostrich feathers? If rubbing an ostrich feather across a solar panel charges up the panel electrostatically (and think of rubbing something on Mars like petting your cat in the middle of a very cold winter, except Mars is really really dry) you are in deep trouble. (obSF: "Dust Rag," Hal Clement).
How do you sterilize an ostrich feather to get it past the planetary protection protocol?
What is your failure-mitigation mechanism for the case the mechanism jams when the feather is halfway across the solar panel? (keep in mind that shadowing just one solar cell in a string will take the entire string off line.)
The dust on Mars is preferentially attracted to magnets.
Mars is very cold, and very dry, and very dusty. What are you proposing to use to lubricate this mechanism? How are you keeping it from jamming? What's your plan to ensure that the acoustic environment inside the launch shroud doesn't vibrate it until the shaft bends? (That long ostrich feather looks like a cantelever that's going to resonate like heck. Tie downs? OK, another few moving parts; more failure modes, more wires connecting to D/A lines connecting to the computer.)
I don't even know what you mean here. There's no free lunch, even on Mars; if you have weights and pulleys moving it one way, you need exactly that much more energy to move it the other way.
Failure analysis is a difficult task, and it's the failure modes that you don't think of that kill you. I'm hard-pressed to think of mechanical devices that work reliably for ten years with no servicing in severe environments on Earth, and you're proposing close to zero chance of breaking on Mars. My car's windshield wipers get a little unreliable at merely 0F; I don't think I'd like to claim "no chance of failure" at, say, -50.
....although it may seem like it, my point here is not merely to poke holes at superficial solutions (to be fair, you did say "off the top of my head."). The point is that space is not like Earth, and there really are reasons that it is harder to do things in space than it is on Earth. Something like you propose probably could be made to work, but your offhand thought that oh, it would be simple and cheap and reliable is just offbase.
Re:Dust removal, hard but possible (Score:5, Informative)
Yeah, both of these were looked at. We thought about miniature piezo vibrators on the cells, but didn't actually get to the point of doing any tests under Mars conditions. We did a bit of work with electrostatics-- in fact, the mitigation technique I like best right now uses a DC glow discharge ("Paschen discharge") which is pretty easy to start at Mars pressure, very near the Paschen curve minimum.
Re:Stupid but obvious (Score:2, Informative)