Interplanetary travel, Arctic sea ice

[rootone]

Are you expecting to find pure metals out there? From what I have read, metals will be in the form of ores, which need to be extracted. The reducing chemicals would need to be imported in comparable mass to the metal you get out.
I think you need to rethink your proposal to take that into account. Processing pure metals is the least of your problems.

At a stretch I guess you could have supporting spacecraft delivering hydrogen obtained from the outer atmosphere of Jupiter
Doubtful economics for that though it might work in principal

 

[JMz]

Is H held by Jupiter any easier to fetch than anywhere else? It's held there because of the deep gravity well, right? So it seems like it would be energetically expensive to deliver from Jupiter.

 

[stefan r]

At a stretch I guess you could have supporting spacecraft delivering hydrogen obtained from the outer atmosphere of Jupiter
Doubtful economics for that though it might work in principal

Extracting things from Jupiter is harder than lifting them from earth.

...3D printed of course...

When you need millions of copies of a large simple 2D structure using a 3D printer is not the easiest way to do it.

The structure would be 'open' and, as I mentioned above, the best construction may not be with sheets (an intermediate process needed) but fused pellets...

I am fairly confident that sheets have more shadow than pellets.

Space communications, astronomy and even transport could be affected.

How are space communications effected by anything at the sun-earth L1? A solar screen would certainly effect solar astronomy if observed from Earth. I think you could get around that problem. What sort of transportation passes through L1?

 

[sophiecentaur]

When you need millions of copies of a large simple 2D structure using a 3D printer is not the easiest way to do it.

Yes. I get that but 3D printing / casting of substructures could be the best of both worlds. But the "pixel" size wouldn't be small, would it? My point is that rolling out strip may not have the advantages that it has on Earth. Ye gods, I can just imagine the plethora of Artists' Impressions for designs. All beautifully air brushed and coloured.

How are space communications effected by anything at the sun-earth L1? A solar screen would certainly effect solar astronomy if observed from Earth. I think you could get around that problem. What sort of transportation passes through L1?

That's a point, I guess. Few Astronomers actually look in the direction of the Sun and likewise for space journeys.

I am fairly confident that sheets have more shadow than pellets.

But we don't want to block out the Sun entirely, do we? A 10% reduction in flux would be more than enough for a 'safe' modification. The project would obviously take a while to complete and its effects would be monitored all the time.

 

[stefan r]

I found an article describing how to move the Earth to keep temperatures down.

But we don't want to block out the Sun entirely, do we? A 10% reduction in flux would be more than enough for a 'safe' modification.

I believe a 10% reduction would be overkill. Likely set off a snowball earth. The number mfb gave in post #6 is 1%. I remember hearing 1% as an estimate of the warming but I do not recall the source.
We also do not necessarily need to restore temperatures to the historical normal. The original post was asking for a megastructure that will prevent a run away positive feedback cycle. Something smaller might be enough.

Ye gods, I can just imagine the plethora of Artists' Impressions for designs. All beautifully air brushed and coloured.

The effect would be black since we only remove light. It is also limited to the angular diameter of the sun. You could do a corporate http://facthole.com/post/133974507954/trump-campaign-unveils-new-logo or maybe the air force roundel of some country.

 

[JMz]

I found an article describing how to move the Earth to keep temperatures down.

Yes, as I recall, this isn't energetically unreasonable -- something like 1 km per year -- IF you have a sufficiently advanced technology. As we presumably will by the time we REALLY need it, when the Sun turns into a red giant. (Moving would take ~100 M years. :-) But it doesn't strike me as a realistic idea for the current problem, anthropogenic global warming. [FWIW, that link seems to be dead.]

 

[stefan r]

Yes, as I recall, this isn't energetically unreasonable -- something like 1 km per year -- IF you have a sufficiently advanced technology. As we presumably will by the time we REALLY need it, when the Sun turns into a red giant. (Moving would take ~100 M years. :-) But it doesn't strike me as a realistic idea for the current problem, anthropogenic global warming. [FWIW, that link seems to be dead.]

All of arXive.org is down. Here is a pay version.

They intend a ~6000 year orbit and it only works when the planets line up. The last paragraph points out this problem too:

An obvious drawback to this proposed scheme is that it is extremely risky and hence sufficient safeguards must be implemented. The collision of a 100-km diameter object with the Earth at cosmic velocity would sterilize the biosphere most effectively, at least to the level of bacteria. This danger cannot be overemphasized.

Not sure why they did not use a large number of small objects.

Asteroid mining would take at least a decade before sun shades were in place. Sun shades launched from Earth using falcon heavy rockets would have to cancel the greenhouse effect from the exhaust. Mylar is 7 gm/m² so a 21 ton payload would be 3 km². For 2 x 10⁶ launches add around 2x10⁹ tons of CO² (a few weeks at current emission rates). Should cost less than $10¹⁴.

 

[JMz]

A bargain at twice the price! ;-)

 

[mfb]

Anything large in space would probably start with tens of billions spent on systems that can bring more stuff to orbit. Something like the StarTram or an orbital ring. Or a StarTram building an orbital ring. Tens of billions of initial investment, but afterwards you can launch thousands to millions of tons to space every year for not much more than electricity costs.

 

[sophiecentaur]

A bargain at twice the price! ;-)

A bit more costly than spray paint, I think.
How much would costs need to shrink for the space approach before it was a serious competitor?

 

[stefan r]

A bit more costly than spray paint, I think.
How much would costs need to shrink for the space approach before it was a serious competitor?

Suppose paint costs $5 per liter and covers 10m²/L, $5x10⁵/km². The surface of Earth is 5 x 10⁸km². You need to paint more than 1% because the surface already reflects some light. Desert sand has albedo 0.4 and paint might be like fresh snow at 0.9 (assume 50% change). Reflected light also passes through the atmosphere so ~30% is absorbed.
5x10⁵/km²x 5 x 10⁶km² x 0.5 x 0.7 = $7.75 x 10¹¹ minimum for paint. More if the surfaces are not flat, maybe $150 billion.
The labor costs would greatly exceed that. Applying exterior paint to a house might be 10x to 30x the material cost. Some labor saving tricks could increase the materials used by painting inside crevasses and double coating some spots. Maybe $5 x 10¹².

Bulk polystrene cups sell for ~$2000 per ton. A ton of tiles 5mm thick and 16 kg/m³ would cover 0.0125 km². The albedo of ocean water is very low so we can use 80% albedo gain so 100 ton/km². 5 x 10⁸ tons cost $10¹². Labor cost would be negative because the commodity price includes a bulk delivery. A refinery could be located adjacent to the ocean and utilize natural wind and water currents.

We could also use aluminized plastic sheets. Air and water slowly pass through plastic so you would need to fill bubble wrap with freshwater to float it. Plastic sheets would be thinner than polystyrene but similar in area density and cost. Plastic sheets can reduce evaporation and waves. That adds more variables. With plastic sheets deployed vertically we could tamper with ocean currents.

Aluminum discs or shallow cone with small flotation pockets would cover slightly more ocean area than air/water filled aluminum cans. Wikipedia says 70 cans per kg so maybe 1000 ton/km². Aluminum costs around $2,000/ton. Covering 6.25x10⁶km² costs $1.25x 10¹³. Price might be lower if you use a thinner aluminum film to waterproof a plastic foam or wood fiber board.

$10¹⁴ for Lagrange
$5x 10¹² for graffiti
$10¹² for polystyrene foam
$10¹² for plastic bags
$10¹³ for aluminum cans

Using 500 million tons of polystyrene foam to counter global warming is probably the best suggestion if you are chatting with an environmentalist in the real world. :) Encouraging littering could cut the costs of garbage removal and the construction cost of land fills. You could give tax breaks to outdoor restaurants in Seattle and New York when they serve on Styrofoam and they remove trashcans.

Launch costs need to come down by about x20. There might be some other benefits/costs to consider. Reusable rockets are also weapon systems for example.

 

[sophiecentaur]

Desert sand has albedo 0.4

Deserts are not only sand, you know. Sand dunes are constantly moving so they would be a poor surface to paint. Rock and boulders are more stable.

 

[stefan r]

Deserts are not only sand, you know. Sand dunes are constantly moving so they would be a poor surface to paint. Rock and boulders are more stable.

The wikipedia entry only had "dry sand" on the chart. I assumed that a grain of sand has the same albedo as a similar shaped boulder made of the same materials. Is that wrong? Sometimes smooth surfaces reflect/refract better than pitted surfaces. Painting gypsum or diatomaceous limestone will not do much. The chart has desserts around 27 or 28% albedo but I think that includes cactus and clay.

Carefully selecting the darkest rocks only could boost albedo from 10% to 90% instead of 40% to 90% but most of the cost is labor. Teams hauling barrels of paint on donkeys/camels to areas with no roads would be expensive.

Based on experience with drywall I suspect gypsum dust would spread around in windy deserts. Strip mine it on windy days?

 

[JMz]

And how is all this related to the OP...?

 

[sophiecentaur]

Teams hauling barrels of paint on donkeys/camels to areas with no roads would be expensive.

Have you heard of aerial application? They have aeroplanes these days, you know. And they would be available even now. No need to wait until the cost of big rockets comes down. I guess some people like a space solution

And how is all this related to the OP...?

2. Restoring multi-year sea-ice in the Arctic.

 

[stefan r]

And how is all this related to the OP...?

I read the original post as "what engineering options could force global cooling to preserve or create arctic ice". And a second question about traveling on asteroids.

...
Question:

Is there a plausible way to deploy what amounts to an orbiting 'solar-shade', permanently positioned to cast a shadow over the Arctic, thereby enabling the restoration of some of the multi-year sea-ice which has been lost?

Assuming such a structure could even be assembled, I believe it would require daily re-positioning, hence a design which would benefit from either the use of solar-wind, or some other extraterrestrial fuel source.
...
Given the remarkable advances in recoverable booster-rocket technology we're witnessing...