Got Dust? Acoustic Levitation Might Clear It

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Like my Martian camouflage? NASA’s Mars Expedition Rover Spirit showing off her red solar panels after years of dust collection exploring the red planet (NASA).

Although we are currently eying Mars as a possible destination for a human expedition, it doesn’t mean we are going to be landing on a hospitable planet. It’s freezing cold, dry, humming with radiation and there’s nothing but dust. Lots and lots of dust.

Now scientists at the University of Vermont think they have a solution to the dust problem: acoustic levitation, a method that could — quite literally — lift dust off any desired surface.

Dust? Is that really an issue? After all, that factor is likely to be the least of our problems on Mars. Working out what to drink and eat will be the primary concern as soon as we land. We’ll be like hi-tech cave men, trying to use any local shelter to hide and using whatever materials we can gather for industrial and construction purposes.

A Dusty Conundrum

Wind whipping up a dust storm on Mars as seen by NASA’s Mars Reconnaissance Orbiter (NASA).

However, the enduring presence of Mars dust will coat everything it touches; clogging mechanical joints, coating solar panels, scratching helmet visors and possibly causing respiratory problems when we breathe it in.

We already have experience of space dust on human activity in space. On the moon for example, the Apollo astronauts reported a multitude of problems with moon dust, a material not unlike Mars dust. Both are known as “regolith,” a finely ground, pulverized material that comes from eons of meteorite impacts.

As the Martian atmosphere is very thin and dry, erosion processes are very slow to wear down the regolith. On Earth, dust, sand and rocks are worn down by atmospheric weathering (i.e. they are smoothed), but on Mars the regolith stays sharp, jagged and electrically charged (static), a sworn enemy of any man made product that should trundle across the Martian landscape. At best it might scratch the UV protective layer off a visor, at worst it could compromise an airlock seal, leading to depressurization (and a nasty death).

Whistle That Dust Away

But there could be a Space Age solution to this Space Age problem. No, it doesn’t involve cumbersome “dust wipers” and there’s no “compressed air blowing device” either. This solution uses sound waves to ‘lift’ the dust off a protected surface.

“[The researchers] found a high-pitched (13.8 kHz, 128 dB) standing wave of sound emitted from a 3 cm aperture tweeter and focused on a reflector 9 cm away was strong enough to dislodge and move extremely fine (<2 µm diameter) dust particles on the reflector surface. The sound waves overcome the van der Waals adhesive force that binds dust particles to the surface, and creates enough pressure to levitate the dust, which is then blown away.” –Lin Edwards, Physorg.com

In other words, using fairly inexpensive and readily available parts, a high-pitched whistling device could force the dust grains from the surface, overcoming any electrostatic force binding the dust to the surface. (Out of interest, the frequency used is slightly less than the frequency a dog whistle generates — 16 to 22 kHz — so the Mars Rovers will go crazy!)

A dust-covered Apollo astronaut working on the lunar surface (NASA)

Problem Solved?

Although this might sound very exciting, there’s one major drawback to using an acoustic levitation device on the moon or space. There’s no air!

Sound waves require air to propagate through. All the tests carried out by the Vermont team were done on Earth, at atmospheric pressure. In space, there is no air and therefore no sound (we all know that in space no one can hear you scream). Any external applications that this device might have for a space station or on the lunar surface have suddenly been lost. But what about Mars?

Although Mars has an atmosphere, acoustic levitation probably won’t work there either; the atmospheric gases are too thin. The low pressure stifles acoustic wave propagation. It is conceivable that this technique could be used inside space stations, pressurized rovers and Martian habitats to clear dust from consoles and interior windows, but one would hope that habitable spaces will be clear from dust in the first place.

So, as for long-term robotic missions using solar panels, perhaps a compressed air device to blow away the dust wouldn’t be such a bad idea after all…

Source: Physorg.com