h a l f b a k e r y
I like this idea, only I think it should be run by the government.
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No real need to carve them either, just send up a mold full of water |
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Except that the effective temperature in space, where Earth is, works out to about 7degC, or 45degF. |
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You might want to get them a bit farther away from the sun before you set them adrift in space. It gets colder when you go out towards Mars. |
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Seriously?? it's 7c in orbit? that's surprising. |
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How soon can you get the ice sculpture out of the Solar System? |
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How soon do you want 'em? :) |
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if a flake of paint in space can do serious damage what chaos could a chunk of ice do? I'm surprised by that temperature too - you just imagine its pretty chilly. |
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I've got a feeling that water ice sublimes in a vacuum, but I'll have to find a reference.
Maybe with a few orbital lasers, we could remotely sculpt comets. |
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Water ice will sublimate in a hard vacuum at temperatures above about -13C / 9F / 260K, I think. |
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The temperature of an ideal flat plate in constant, direct sunlight in near Earth orbit (around 300km) unrestricted by atmosphere or dust would settle at a temperature around 394K / 121C / 250F. This is because the sun delivers a constant 1367W/m^2 to the body at this distance. That temperature would be the equilibrium point for a perfect object in space allowing for black body radiation, only, to mitigate its temperature. |
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However, there are a number of other considerations not in that example that we must take into account:
1. It's an “ideal” flat plate, always perpendicular to the sun at its highest intensity at 1AU. That won't happen, unless it's in circumpolar orbit with nil eclipse time (behind Earth) and there is absolutely no randomised spinning of the plate.
2. The example is for an object with an absolutely imperfect albedo of 0.0 assumed. It should be about 0.30 average, depending upon seasonal fluctuations and a few other factors. Albedo ranges between about 0.25 and 0.35, depending upon the elliptical nature of Earth’s orbit and season and angle of Earth’s rotational axis, and whether our ideal plate is aligned perpendicular to Earth’s surface or the sun’s light.
3. Perfect thermal radiation of the bright side of the Earth was assumed. Also impossible. In fact, in a circumpolar orbit the plate would always have a thin (negligible, as it's ideal) edge facing the earth, so thermal radiation is exaggerated in the above example, in effect. |
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In reality, the effect of the black body radiation factor (the tendency for such a body to also give up its heat) will be aided by the fact the object is rarely at a perfect angle, is often obscured from sunlight (about 48% of each orbit of the earth, assuming it has an orbital path similar to that employed by the space shuttle missions). That lowers the average surface temperature of the body to between +7 and +8C. A thermometer in orbit at that altitude would reach an equilibrium temperature of about +8C / 281K. |
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The first part of my statement was unfortunately predicated upon a number of assumptions that can only occur in a thought experiment. |
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The same thermometer, constantly isolated from solar radiation (in shade) is still exposed to the thermal radiation of Earth and will show an equilibrium temperature of about 236 K (-37 °C) given that Earth's average surface temperature is about 287K / 14C / 57F |
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A thermometer far away from any direct heat source in space will still receive the cosmic microwave background radiation. The equilibrium temperature there is about 2.7K / -270C / -455F. This is where the confusion comes about, because this is the temperature we associate with space. It's really the temperature of deep space, well away from solid matter, stars or gas clouds. |
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Much thanks to UnaBubba for the math. Until it's well beyond the orbit of Mars, at 1.5 AU, the ice is in danger of evaporating -- it's "hb's comet", not the more desirable "hb's irradiated giant llama-sicle ambassador to the stars". Hence the suggestion to the get it further away from old Sol, so that it's just sublimating. |
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[simonj], I thought the gold record idea was silly. But nobody asked me at the time. |
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//giant ice sculptures of Earthly animals//
Why not actual animals? What else are we going to do with the elephants? |
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Bad Science - the ice will evaporate long before it gets to the stars. Heck, try it in your fridge - haven't you notice the ice cubes in your ice trays steadily evaporate? Just imagien how much faster that will go in a vacuum. |
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However, you could probably fix that to a large degree by plastic coating them, or some such. And I do like the idea of inflicting ice sculptures on our near galactic neighbors. |
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I'd like to make an enormous ice sculpture of David Bowie in space. That's pretty far out man. |
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Wow, [UB]! Most impressive math and knowledge. As always. (I've often wondered at those claims that the inside of freshly-fallen meteorite are incredibly cold--now I'm sure they are wrong.) |
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[DrC] I thought that only modern frost-free freezers have that ice-subliming problem. Older ones tend to build up crystals all over. Which suggests your plastic idea is good. |
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May I suggest a big plastic bubble, rather than a hard, shaped coating. If the bubble has enough vapor in it, the ice should not sublime. If it could be rigged to pop once far enough from the sun . . . |
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[Unabubba] I have to quibble with your
thermodynamics. You first say that,
because the sun delivers X power, an
ideal flat plate will reach 121C. |
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You *then* add in black-body radiation
which dissipates energy and brings it to
a lower equilibrium temperature. |
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However, without black-body radiation
(as per first para), and with constant
energy input, the plate will reach an
arbitrarily high temperature - why
would it stop at 121°C? |
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So, it may well equilibrate at 7°C, but
the reasoning by which you get there is
screwy. |
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//David Bowie in space//
Switch on the TV, we may pick him up on Channel Two. |
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I think we should launch space rockets full of water from Canada into orbit, make ice cubes, and then drop them over the Sahara. Eh. |
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No, my humor is not good this morning. Need something fresh to wake me up. |
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//Bad Science - the ice will evaporate long before it gets to the stars//
If that were true, all those comets in the Oort cloud would have evaporated over the past 4 billion years or so. |
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But, [Unabubba], even if you grant those
assumptions, it's still wrong. |
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Before you introduce black body
radiation, your plate has no means of
losing heat. Hence, it's nonsense to say
that it will "settle at a temperature of
around 121C", or any other temperature
- it would just get hotter until it
vapourized. |
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Equilibration is only possible because of
black body radiation. |
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Yay, [django] has reappeared! Wasn't he missing last month? |
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For all we know, the objects in the Oort cloud used to be bigger. |
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I have another concern. Would the admittedly small gravity of the chunk of ice gradually pull it into a spherical shape? If so, how long would that take? |
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I doubt there would be sufficient gravity to have any impact on the ice. Ice is viscous, but not terribly so. |
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If it was a factor then comets would be perfectly spherical. |
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// Ice is viscous, but not terribly so//
Both untrue. Ice is crystalline (as opposed
to, say, glass, which is not), and hence it
requires a finite force to distort it at all. In
this sense, the term viscosity doesn't
apply. Also, what you meant to say was
"very viscous" (ie, very thick like glass, not
runny like water), even though the term
doesn't apply. |
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"Would you like ice in your drink?" -
"Viscous or crystalline?" - "hmmmm
that's a tough one, can I phone a
friend?" Nice idea, by the way [simonj].
+ |
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Even rock is viscous, strictly speaking, [MB], though over very long timeframes and under very great pressures. |
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The level of granularity of the crystalline structure affects the viscosity, as you point out, but ice still flows. Witness glaciers and ice sheets. |
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As I stipulated in my answer, I doubt there would be enough force to move anything in a sculpture of this type. It's similar to the mistaken belief that a pane of glass "flows" downward over time. It will, in something like 1 x 10^13 years, under Earth's gravity. |
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