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Earth density ~ 1g/cm^3 = 1000kg/m^3 ~ Asteriod density Asteroid Radius = 1km. Asteroid mass = 4/3piR^3density = 4.2x10^12kg

acceleration = G M/R^2 = 280 micrometers/second

if initial velocity is zero, a dust particle will settle in about 300 seconds from a height of 10m at this acceleration.

They can always escape if initial speed is high, but if not, they will settle down pretty fast.

Use science!

Earth's density is 5.5g/cm^3. Asteroid densities vary, averaging maybe 2.5g/cm^3. Metallic asteroids are about 5g/cm^3.

Wouldn't the dust just slowly deposit itself? 10,000 years sounds a bit much. The moon does have some gravitational pull, and there being no air resistance or viscosity, my guess would be much shorter than 10,000 years... maybe just hours or days. (Talking about the moon, not small asteroids - for these I guess dust can even escape them).

Asteroids have negligible gravity. Solar wind is miniscule so far from the Sun (twice as far as the Earth, 1/10 the radiant effects). Mining generates prodigious amounts of dust. It would grow linearly until you were operating essentially in a dense field of dust. It would stay - maybe not 10,000 years, but forever for mining purposes.

No, you'd be surprised. You can do an experiment where you just take 2 large masses (say bolders) and put them across from each other with a suspended balance-bar in the middle (suspended from the ceiling so that it spins freely). Over the night the bar will align to the masses via gravity.

Can't find the experiment because of no keywords for it I can think of, but this shows that even a few 100 kilos have real amounts of gravity.

Edit: Here it is: http://en.wikipedia.org/wiki/Cavendish_experiment

My first reaction to this conversation was to imagine some kind of vacuum hose attachment. My second thought was "oh yeah... that won't work at all" :)

I had the same reaction - actually, I was thinking in some sort of spatial hoover - but I am still trying to work out in my mind if it would work. Can you explain how you came to the conclusion it wouldn't?

It would have no way to generate suction. However, if you moved the space hover INTO the dust, you could have a mechanical trap inside.

EDIT: Looks like I was a bit late, I wrote this comment ~hour ago but didn't post it till now. :P

There's no air.

Exactly, I almost facepalmed when I realized the absurdity of a vacuum hose... although I do wonder if something along the lines of a CO2 compression canister would work to blow away dust. I'm assuming that it would be prohibitively expensive to have to constantly ship compressed gas to the mining site though.

That's why you'd just ship an asteroid that's already made of gas and liquid, and mine that for your gas.

"Evaporate some more nitrogen off that asteroid, Joe, we need to blow this dust away."

And to be specific, vaccums work by creating a low pressure locality inside of a gas. Same principle behind a backwards fan. Push the gas one way, you create a small low pressure point that other gas then fills. In a vaccume-cleaner the region of gas that can rush in to fill the low pressure point is at the end of a nozzle.

Really, you're not vacuuming up objects, they're just along for the ride in their immediate atmosphere.

(...And in space, you have no atmosphere to manipulate.)

A roughly spherical asteroid of radius r has volume

4/3 * pi * r^3

Using Ceres as a benchmark for typical asteroid density, an asteroid of radius r has mass

[volume in meters^3] * 2077 kg/(m^3)

On the asteroid's surface, acceleration due to gravity is

[Gravitational constant] * [mass in kilograms] / (r in meters)^2

which simplifies to

(6.67384E-11 * 4/3 * pi * 2077 * r) m s^-2

If we mine on a 1km diameter asteroid, the dust we kick up will accelerate towards the surface at 2.9 * 10^-4 m/s^2. A dust cloud 10 meters high will settle in about five minutes.

Spin up the rock. Just make sure all of your equipment is bolted on tight.

Lovely responses, I'm gratified to see so much interest in this topic.

Have to observe though, its pretty easy to make things work out by assuming a planetoid or large asteroid. Yet the vast majority of objects in the asteroid belt are under half a km in radius. Prospectors don't get to pick where the metals are. And by mass, or count, or chance, its overwhelmingly likely to find it in one of the small asteroids.

If you assume towing an asteroid into orbit and then mining, now we know its a tiny asteroid and the dust is still a problem. However it seems foolish in the extreme to haul gigatons of slag to orbit and then mine it, instead of just hauling back the valuable stuff. The energy costs are going to make or break the feasibility of any space mining project.

If the mining isn't automated - that is, if mining requires a human presence - it hauling the gigatons to Earth orbit might not seem to foolish. Aside from the cost of having to ship people, equipment, air, water and food to the asteroid belt, an accident in Earth orbit is much easier to deal with than one past Mars orbit.

"Don't worry, Miner Mike - a Space Ambulance is on its way! Just hang in there for four or five more months."

> No gravity or wind to blow away dust - it will just hang there, for 10,000 years, a growing problem as mining activities continue.

Not without an atmosphere. Even a small asteroid has enough gravity to cause dust to settle to the surface rather quickly -- or move away if the dust particles have escape velocity or greater.

> Then, when a chuck of material is gotten loose, it will just drift away ...

Yes, if the object is given an initial velocity greater than escape velocity. Otherwise it will return to the surface, but it won't just drift about.