Author Topic: Sun Shade concepts for Venus  (Read 89551 times)

Offline Da5id

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Re: Sun Shade concepts for Venus
« Reply #80 on: 02/03/2012 11:29 am »

Has anyone tried this in the lab to see if how much if any amount of Sun radiation ( type that would heat Venus atmosphere and surface mass ) would be blocked by this idea?

Any idea how much power just the lasers would need?

No power at all because the physics is wrong. See Sohl's original post.

 The physics is wrong because Sohls interpretation of the original idea is wrong.
Light through a translucent medium will fade out light eventually, depending on it's density.
« Last Edit: 02/03/2012 01:50 pm by Da5id »

Offline dcporter

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Re: Sun Shade concepts for Venus
« Reply #81 on: 02/03/2012 02:26 pm »
So you're saying fog alone should do this? The lasers are just for fun?

Offline Da5id

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Re: Sun Shade concepts for Venus
« Reply #82 on: 02/03/2012 02:55 pm »
So you're saying fog alone should do this? The lasers are just for fun?

The Multiple layers of Lasers do the work of colour subtraction dimming in turn the next level of fog  down and so on, so the complete fog would not need to be so dense.

Correction:That of course would be additive not subtraction in colour. I made a mistake in the description.
« Last Edit: 02/10/2012 10:38 am by Da5id »

Offline Sohl

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Re: Sun Shade concepts for Venus
« Reply #83 on: 02/03/2012 06:36 pm »
"The Multiple layers of Lasers do the work of colour subtraction dimming ..."

[ smacks forhead ]  In the chance you are not just goading me, I will try one more time.

Shining light is not subtracting.  It's adding.  Subtractive colors need pigment,  not laser light.  Pigment particles absorb the incoming light and then readmit that energy in a lower frequency form, like UV->visible light with florescent paint or increased thermal energy in the pigment itself (black paint heats up more than white).

Of course fog will dimish light, mostly by scattering it in different directions and perhaps  some modest amounts of absorbtion. If the fog is thick enough, it will shade the ground/object which would otherwise be lit and heated by the Sun.  All by itself. 

Adding _more_ light with lasers will not help it block more light.  The one exception is if the lasers somehow trigger a photochemical change in the fog droplets or cloud particals so they absorb or reflect light differently than they did before.  But it would be far easier and probably much more efficient to form your fog or cloud out of something already relatively good at absorbing or reflecting.  In other words, make a cloud out of stuff that is already a good pigment.  Or make it out of something already reflective.  Snow?  Won't stay frozen there, but I hope you get the idea.  You don't need lasers.  They won't help at all with the vast majority of materials you could make a cloud out of.  They may look pretty.

RocketmanUS said "Experimentation over what we think".  Yes I agree.  I would propose the following:

1) Get a nice strong spotlight that provides a color spectrum similar to the Sun.

2) Shine it at a target several feet away.  Measure the brightness.

3) Get a glass box.  Fill it with whatever fog/cloud you want.  Dry ice in water?  Stage fog?  Wood smoke?  Carbon dust?  I don't think it matter much.

4) Put the box in the path of the spotlight beam.  Measure the amount of light at the target, now reduced by some % from the no-box case.  Also observe the beam from the side as it passes through the box.  You will see it "light up" the cloud in the box. If the cloud is thick enough, you might even notice the cloud is brighter on the entry side than the exit side, just as you would expect from cumulative dimming.

5) Now shine whatever combination of lasers into the cloud in the box.  You can make curtain patterns or whatever pattern you like. Then measure the amount of the light reaching the target. 

My prediction is that you you won't get less of the spotlight beam getting through.  You seem to think it will.  If you are in the visual arts, you should be able to set up a stage with this experiment.  Try it and tell us what happens.
In fact, I am very certain it will be slightly _higher_ than the previous step if anything, because you are pumping _more_ light into the box and some of that additional light will be scattered toward the target. 

Offline Da5id

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Re: Sun Shade concepts for Venus
« Reply #84 on: 02/03/2012 10:49 pm »


My prediction is that you you won't get less of the spotlight beam getting through.  You seem to think it will.  If you are in the visual arts, you should be able to set up a stage with this experiment.  Try it and tell us what happens.
In fact, I am very certain it will be slightly _higher_ than the previous step if anything, because you are pumping _more_ light into the box and some of that additional light will be scattered toward the target. 

Well using the combination of laser as I mentioned earlier I think it may come out a very very translucent  brown, (If the laser curtains can act similar to a gel filter that is).
  How ever I do not have access or resources to set up such experiment. It does give me food for thought.

I would like to thank every one for the replies, Its probably clear I'm thinking way out side the box.
« Last Edit: 02/03/2012 10:50 pm by Da5id »

Offline RocketmanUS

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Re: Sun Shade concepts for Venus
« Reply #85 on: 02/03/2012 11:40 pm »


My prediction is that you you won't get less of the spotlight beam getting through.  You seem to think it will.  If you are in the visual arts, you should be able to set up a stage with this experiment.  Try it and tell us what happens.
In fact, I am very certain it will be slightly _higher_ than the previous step if anything, because you are pumping _more_ light into the box and some of that additional light will be scattered toward the target. 

Well using the combination of laser as I mentioned earlier I think it may come out a very very translucent  brown, (If the laser curtains can act similar to a gel filter that is).
  How ever I do not have access or resources to set up such experiment. It does give me food for thought.

I would like to thank every one for the replies, Its probably clear I'm thinking way out side the box.

Might try contacring Mythbusters. They could if they like the idea for their show set up some experiments, your idea and the solar sail idea.

For the solar sail idea. Place an ice cube on a plate and shine a heat lamp on it from several feet away from above. Time how long it take to melt the ice cube. Now do the same but with a piece of refective mylar ( from helium baloon ) between the heat lamp and the ice cube so the mylar will cast a shadow over the ice cube. Do this indoors with the inside temp around 70 to 80 deg fahrenheit, have the room temp the same for both with and without the mylar shade. Now try an ice cube on the plate without the heat lamp so we know the rate it melts at room temp. This all has to be done away from an open window so that the Sun's light will not play a part in the experiment ( best at night ).

My take is the unshaded ice cube under the heat lamp will melt fastest. The shaded ice cube under the heat lamp will melt slower and the ice cub with no heat lamp will melt the slowest.

You could also try this with colored filters instead of the reflective mylar to see what type of results you get. Not the same as the fog and laser though. Keep in mind that fog can reflect and or refract laser light.

Offline dcporter

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Re: Sun Shade concepts for Venus
« Reply #86 on: 02/04/2012 02:47 am »
Well using the combination of laser as I mentioned earlier I think it may come out a very very translucent  brown, (If the laser curtains can act similar to a gel filter that is).

They don't act like gels. Adding lasers together makes more white light not less brown light. Think of it this way: the gels are colored before the light comes along; the fog wouldn't be colored until the laser light shows up. That means you're adding instead of subtracting.

Offline RocketmanUS

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Re: Sun Shade concepts for Venus
« Reply #87 on: 02/04/2012 03:08 am »
O3

If we made O3 from CO2 and the extra carbon made a ball out of it to drop to the surface.

So if we released O3 in the upper atmosphere would this help reduce heating?

Offline Da5id

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Re: Sun Shade concepts for Venus
« Reply #88 on: 02/04/2012 08:23 am »
Well using the combination of laser as I mentioned earlier I think it may come out a very very translucent  brown, (If the laser curtains can act similar to a gel filter that is).

They don't act like gels. Adding lasers together makes more white light not less brown light. Think of it this way: the gels are colored before the light comes along; the fog wouldn't be colored until the laser light shows up. That means you're adding instead of subtracting.
I think what best Im trying to describe or set up is levels of holograms acting as filters. (removing the need for fog altogether) .

Offline douglas100

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Re: Sun Shade concepts for Venus
« Reply #89 on: 02/04/2012 09:38 am »

The physics is wrong because Sohls interpretation of the original idea is wrong.

Light through a translucent medium will fade out light eventually, depending on it's density.

No, your idea is wrong. You can't block light with light.
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Offline Da5id

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« Last Edit: 02/05/2012 05:24 pm by Da5id »

Offline RocketmanUS

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Re: Sun Shade concepts for Venus
« Reply #91 on: 02/06/2012 06:50 am »
Terraforming Venus

When to cool it down?

To cool Venus down we need to block the heat source.

Or we need to change the atmosphere and most likely the planets rotation speed around it's axis to about a 24hr cycle.

Bringing the day cycle to around a 24hr time frame should calm the winds down.

So it probable is a better idea to look to see what type of atmosphere Venus will need to support human life, animals , and plants ( more Earth like ). What would the pressure need to be at different altitudes. What would the N2,O2,CO2,H2O, ect. percentages need to be. Would there be an O3 layer. Knowing what it all needs to be first will help us know how best to go about terraforming Venus.

So we might start by changing the ratation speed of the planet about it's axis. Then start the conversion process of the atmosphere. So how can that be done? That would most likely bring the temp. down to were we need it to be. So there might not be a need to block the Sun light? 
« Last Edit: 02/06/2012 06:52 am by RocketmanUS »

Offline douglas100

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Re: Sun Shade concepts for Venus
« Reply #92 on: 02/06/2012 08:43 am »



 You can't block light with light.

I beg to differ.
http://www.livescience.com/8012-twisted-physics-scientists-create-light-knots.html
But It can be manipulated.


You are correct that light can be manipulated. But my point still stands. The article you cite is about holograms. A hologram is a physical object which intercepts the light. A giant hologram put in front of Venus would certainly reduce the amount of light reaching the planet. But that is not what was being proposed.

I wasn't going to post on this thread again, having criticised the need to ever attempt to terraform Venus and the enormity of the effort required to do it. It is a task for a civilisation well up the Kardashev scale. But treating it as a purely theoretical exercise, the most straightforward way to shade Venus using foreseeable technology would be to use a very large number of solar sails. I think that a single giant shade would be very difficult to make and would be subject to tidal forces that would make it hard to control. A cloud of billions of small solar sails, each kilometers in size and independently maneuverable would be a better solution.

As for spinning up Venus, well it's OT and the effort and energy to do it is magnitudes greater than building a planetary sun shade.

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Offline Sohl

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Re: Sun Shade concepts for Venus
« Reply #93 on: 02/06/2012 05:47 pm »
"I think what best Im trying to describe or set up is levels of holograms acting as filters. (removing the need for fog altogether) . "

Da5id: I think you misunderstand the definition of hologram, and seem to say that any pattern of interference of lasers _is_ a hologram.  It is not. 

You really need to go read a book on electro-magnetic physics, or at least a few chapters on EM wave propogation in a vacuum. A guy named Jackson wrote a seminal textbook used at the graduate level.  There are probably others that would be more accessible to someone at an undergraduate level.

If you cross two or more beams in empty vacuum, the waves of the electro-magnetic field will "interferre" like crossing ripples in a pond, but each beam will travel straight through the others without diminishing.  Another beam (e.g. sun beam) will also travel straight through.  The interferrence pattern from the "hologram" lasers will not inhibit the sunbeam at all. 

It's like you are saying you could set up a few hoppers of pebbles along a beach and have the pebbles drop regularly into the ocean.  The pattern of ripples would interfere and make make a *shield* that would significantly absorb or reflect the incoming waves from the surf, to make it a nice placid beach! Still think it will work?  If you argue the ripples are too small compared to the surf waves, you can make the pebbles as big as you want.  Make 'em house-sized boulders. Won't help.


Offline Rhyshaelkan

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Re: Sun Shade concepts for Venus
« Reply #94 on: 02/06/2012 06:25 pm »
Venus Mass =   4,868,500,000,000,000,000,000,000 kg

As soon as we master space-time to induce a spin on Venus...

Lacking the mastery of space-time we could build a ring that both shades and reflects, to mimic a 24 hour cycle. Early on though it would be 100% shade to reduce temps to something Earth normal. Large quantities of gasses will need to be imported to provide an adequate hydro and nitrogen cycle.
I am not a professional. Just a rational amateur dreaming of mankind exploiting the universe.

Offline RocketmanUS

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Re: Sun Shade concepts for Venus
« Reply #95 on: 02/06/2012 06:45 pm »



 You can't block light with light.

I beg to differ.
http://www.livescience.com/8012-twisted-physics-scientists-create-light-knots.html
But It can be manipulated.


You are correct that light can be manipulated. But my point still stands. The article you cite is about holograms. A hologram is a physical object which intercepts the light. A giant hologram put in front of Venus would certainly reduce the amount of light reaching the planet. But that is not what was being proposed.

I wasn't going to post on this thread again, having criticised the need to ever attempt to terraform Venus and the enormity of the effort required to do it. It is a task for a civilisation well up the Kardashev scale. But treating it as a purely theoretical exercise, the most straightforward way to shade Venus using foreseeable technology would be to use a very large number of solar sails. I think that a single giant shade would be very difficult to make and would be subject to tidal forces that would make it hard to control. A cloud of billions of small solar sails, each kilometers in size and independently maneuverable would be a better solution.

As for spinning up Venus, well it's OT and the effort and energy to do it is magnitudes greater than building a planetary sun shade.


More like 36 million solar sails 1 km x 1 km would effectively cover Venus on the Sun side in low orbit. At a given distance between the Sun and Venus 1,000 solar sails would do the job of shading Venus from the Sun light.

Offline LegendCJS

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Re: Sun Shade concepts for Venus
« Reply #96 on: 02/06/2012 06:58 pm »
Venus Mass =   4,868,500,000,000,000,000,000,000 kg

As soon as we master space-time to induce a spin on Venus...

Lacking the mastery of space-time we could build a ring that both shades and reflects, to mimic a 24 hour cycle. Early on though it would be 100% shade to reduce temps to something Earth normal. Large quantities of gasses will need to be imported to provide an adequate hydro and nitrogen cycle.

Just a calculation fyi, haven't looked to see if it has been posted before.
 The Earth receives ~174 petawatts of energy from the sun.  Solar intensity is a little less than twice as high on Venus as on Earth, and the planets are roughly the same size, so I'm going to say that Venus receives 300 petawatts of energy from the sun.

The rotational kinetic energy of the earth of ~2*10^29 Joules.  The current rotational kenitic energy of Venus is close to 3*10^25 Joules.  So basically 2*10^29 joules of energy are needed to "spin up" Venus.

If some way could be found to convert this solar energy to rotational energy of Venus with 100% efficiency, for sake of upper-bound,  It would take over 22 thousand years to reach anything near a 24 hour cycle.

EDIT: upper-bound in terms of desirability, not time taken.
« Last Edit: 02/06/2012 06:58 pm by LegendCJS »
Remember: if we want this whole space thing to work out we have to optimize for cost!

Offline WellingtonEast

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Re: Sun Shade concepts for Venus
« Reply #97 on: 02/06/2012 08:21 pm »
I think "Patchouli" topic on using asteroid impacts warranted more detailed discussion.
   
We know single volcanic events can impact earth world weather so why is it not feasible that asteroids couldn't do the same for venus.

It is documented that there are smaller asteroids with water ice that we could possibly move one day (using current physics) such as :
http://www.nasa.gov/topics/earth/features/water_ice_asteroid.html

FYI - I am not proposing changing venus spin and moving large asteroids such as Vesta as that is only SCI Fi at the moment like inventing "unobtainium" metals and force fields.

Offline douglas100

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Re: Sun Shade concepts for Venus
« Reply #98 on: 02/06/2012 10:00 pm »
Quote from: RocketmanUS link=topic=26743.msg858985#msg858985

[quote
More like 36 million solar sails 1 km x 1 km would effectively cover Venus on the Sun side in low orbit. At a given distance between the Sun and Venus 1,000 solar sails would do the job of shading Venus from the Sun light.

Yeah, I didn't bother calculating the cross sectional area of Venus. I get about 115 million square kilometers, but you're right that it's millions not billions.

However, you wouldn't want the sails in low Venus orbit, they would continuously collide with each other. It would be better to have them around the the Venus-Sun L1 point. Even there it would not be a trivial matter to control them in such a way as to block all solar radiation from reaching the planet.

I don't know where you get the 1000 figure from. You would need a greater area of sail as you moved the shade away from the planet toward the sun if you still wanted to block all the light.
« Last Edit: 02/07/2012 01:32 pm by douglas100 »
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Offline Andrew_W

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Re: Sun Shade concepts for Venus
« Reply #99 on: 02/07/2012 01:09 am »
"Sun light passing through will project on Venus as a dark brownish hue. That's it"

Sunlight can't be filtered in this way

"Of course the idea hinges on. Can lasers act like a coloured filter?"

No. As has been explained to you again and again and again and...

I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

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