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Daniyal_Ali
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Platinum
Re: how much energy
Daniyal_Ali   3/28/2014 6:16:38 AM
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I agree with Lou too. Do get the answers from Jaffe and share them with us when you get time. Being actively involved in the Renewable Field myself i can say this with great confidence that at the end, the cost effectiveness and overall output yield is the only thing that settles the issue of implementing something at a larger scale or rejecting it completely, even if the idea is unique.
Perhaps as time passes we will be able to manufacture a better technology to cater such ideas with much cheaper and environmental friendly solutions. The main slogan of Solar Panels is to produce environment-friendly energy, isn't it ironic if we use Solar Panels to generate beams that result in harming the environment?
I am eagerly looking forward to more details about this project which would make things clearer.

SiliconGraybeard
User Rank
Silver
Death Rays From Space? Not So Much...
SiliconGraybeard   3/27/2014 4:38:45 PM
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This is a rather old idea; I remember talking about when I was in school, so over 35 years ago, but I think it was an old idea then. The system design has been done so that it all works out on paper, it's safe for birds or small planes flying through the RF fields, or kids who'd wander into the antenna fields. IIRC, C band (approx 4-6 GHz) worked out well. I've seen design approaches that start with acres of solar cells on the moon, because the weak gravity of the moon provides advantages. It also has the disadvantage of two weeks of darkness out of every four weeks. I think satellites, in deep space worked out best.

 

The beam can be as strong or as weak as you want it to be. Microwaves can be focused very well; high gain antennas that can be deployed in space have been in use since at least the late 1970s and reaction wheels for stablizing the satellites are probably older than that. The safe power exposure level of RF for the general public is around 1 mW/sq.cm, so the receiving antenna array has to be large: think square miles, not square meters. (Fun fact: the lowest power limit the FCC issues is 200 uW/sq.cm for the FM broadcast band, where the average person is close to 1/4 wavelength tall and so a very effective receiving antenna. Just sit down to tune yourself out of band.)  Above some fairly low frequencies, you get lower losses by transmitting through the air than by trying to use cable.  It's the reason the phone companies went to microwave links on towers decades ago.

 

In fact, think square miles of solar cells, square miles of antennas, and the "Microwave Power Amplifier Designers' Full Employment Act". The questions about whether it can be done technically are over. Of course it can. The rough questions are whether it could be done without massive amounts of government spending, when virtually every government in the world is on the verge of default from overspending as it is.

 

naperlou
User Rank
Blogger
Re: How much power, indeed ... logistics, and the cost?
naperlou   3/27/2014 1:46:30 PM
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Hank-4: death rays are exactly what this would become.  This is probably the main reason it will not be done.  I have seen examples of technicians working on large radar systems on Navy ships.  Generally there is a bar placed in the mechanism that stops the antenna from rotating.  In rare cases something happens to this and there have been cases where the technicians have been fried.  What will happen with such a large source in space?  As for fried bird, that is a real possibility.  Just look at the latest concentrated solar power (CSP) plant built.  It is responsible for killing lots of birds already, and that is just from mirrors.  We also have the problem with wind power killing birds. 

On the price issue, I fully agree.  There is no way this is 10 cents per Kwh.  Jaffe is supposedly a spacecraft engineer.  He should know that this is not in the realm of possibility. 

What this whole thing strikes me as is an attempt by NASA to get involved in solving the energy problem.  They would want to do that becuase it is getting more attention than space exploration.  Energy is a DOE responsibility and they have the expertise. 

didymus7
User Rank
Platinum
Re: How much power, indeed ... logistics, and the cost?
didymus7   3/27/2014 1:15:31 PM
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I was surprised that the most important aspect was ignored in the article.  How do you get the energy from space to earth?  The atmosphere is a very lossy conductor.  Then again, you'd need to either set aside a large area for a receptor, or the beam has to be very narrow. 

Now, what happens if a flock of birds flys through the beam?  Is there a special on fried 'chicken' at McDonalds?  Does everybody's TV flicker?  Then there are clouds.

Now, how about the orbit of these things?  If it's not geo-synchronous, you'll lose contact at least half the day, then another half, the beam is going though even more atmosphere due to a poor angle.  If it is to be geo-synchronous, do the satellites always see the sun, or will there be blackouts?

It seems to me a lot of things have to be thought out before you start designing hardware.

Bill M.
User Rank
Iron
Re: How much power, indeed ... logistics, and the cost?
Bill M.   3/27/2014 12:47:03 PM
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It isn't clear what type of beam will be used. RF does not seem very efficient as there is too much atmospheric loss, the beam power you calculated is way beyond the capability of any present day RF amplifier, which would need power to operate. Such a process would require a passive device that can convert the collected energy and convert it into a beam (like a magnifying glass).

On another note, what are the environmental effects of the beam in question?

Hank-4
User Rank
Silver
How much power, indeed ... logistics, and the cost?
Hank-4   3/27/2014 12:07:59 PM
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It looks like most of the other posts broach the question, "how much power?". This is certainbly a valid question. I also wonder about the cost figure of 10 cents per Kwh. I'd certainly like to see how this was calculated ... i.e. what assumptions were made. On the logistics side, I think it might be imprudent to quickly discount the "death rays from space" argument. The article talks of RF and then seems to move on to microwaves. If this is the case, then I must logically conclude that there would be a transmitting antenna array/dish for directing the energy toward some receiving station on the ground. What will be the size of the energy "beam"? Probably most important, how accurately can/will this be directed between orbit and the ground? Let's consider some numbers. In the desert SW of the US (and even sometimes in the SE regions), the insolation can reach 1000w/(sq meter). In space, where there is no atmospheric attenuation, that number will certainly be higher ... but let's just use 1Kw/m^2. If the collector array is 1Km x 1Km (implied from the article), then we could expect an array output of 1Mw. For the sake of argument, let's also assume a DC power - to - beam conversion efficiency of 25%. Further assuming a uniform distribution of power across the beam cross section, that would give us a total cross sectional beam power of 250Kw. For a beam diameter of 1m, the power would be approximately 333Kw/m^2. This number would go up for smaller beam diameters and down for larger beam diameters. The positioning of such a beam would need to be VERY carefully controlled.

Bill M.
User Rank
Iron
Re: how much energy
Bill M.   3/27/2014 10:47:33 AM
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Robots are much cheaper to support in space than humans. Humans need food, water, air, companionship, and an environment with tightly controlled temperature range and air pressure. All of this means a lot of weight being sent to space consistently which is really expensive. Robots are more durable. Robots can withstand greater temperature ranges and higher levels of exposure to radiation. Robots don't get tired, bored, or disgruntled. Robots don't have to be brought back to Earth after a relatively short stay.

Bill M.
User Rank
Iron
Efficiency Tradeoff
Bill M.   3/27/2014 9:46:19 AM
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How is the energy harvested to be transferred? Solar panels have greater efficiency and longer life due to lack of atmosphere. However, is it enough to outweigh the efficiency lost in transmission through the atmosphere?

Can we deliver the sun's energy to earth more efficiently than nature does now?

jhankwitz
User Rank
Platinum
Re: how much energy
jhankwitz   3/27/2014 9:39:12 AM
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I would think that robots would be far more desirable than humans because of the added cost and risk associated with life support.  This is supported by our government use of aircraft drones.  These drones are actually robots controlled by humans, as would be the robots constructing the space array.  The space station certainly is not designed to perform array construction, and it would be far to difficult and costly to manuver its own solar arrays around a huge construction site.

Elizabeth M
User Rank
Blogger
Re: how much energy
Elizabeth M   3/27/2014 8:08:36 AM
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Lou, those are good questions, but as to your first I don't think the research has gotten that far. I would have to check with Jaffe. I think the answer may be a bit further down the line, as it hasn't really been tested yet.

And as for the robots, that's also a question for Jaffe. I am sure he has a good reason for including robotic assembly, but I completely see your point that it seems like a lot of effort for something that doesn't contribute to the ultimate goal of the system.

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