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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 1:18 pm 
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Location: Rhinebeck, NY
I propose an alternative to putting the PV in orbit. Instead put a mirror and a lens in orbit. The lens will focus the sunlight to a point on the earth where the PV will convert it 24/7 to electric. I would use a focal length of 20,000 km for the lens. This will mean it will not be overly hot on the PV. The lens can be made of nitrogen gas held between to thin sheets of plastic with the correct radius of curvature. The mirror directs the sunlight to the lens/PV. The mirror is a thin aluminized plastic sheet.

Nitrogen with an index of refraction of 1.0003 works well for this application.


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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 4:42 pm 
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edpell wrote:
I propose an alternative to putting the PV in orbit. Instead put a mirror and a lens in orbit. The lens will focus the sunlight to a point on the earth where the PV will convert it 24/7 to electric. I would use a focal length of 20,000 km for the lens. This will mean it will not be overly hot on the PV. The lens can be made of nitrogen gas held between to thin sheets of plastic with the correct radius of curvature. The mirror directs the sunlight to the lens/PV. The mirror is a thin aluminized plastic sheet.

Nitrogen with an index of refraction of 1.0003 works well for this application.



So in other words put a large magnifying glass in geostationary orbit, exactly like kids frying ants or a "solar concentrator". I imagine this would have a significant effect on temperatures as the column of air the beam transits is heated by the extra light...which generates wind and, if large enough, disrupts weather patterns.


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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 5:53 pm 
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Location: Albuquerque NM USA
Cthorm wrote:
edpell wrote:
I propose an alternative to putting the PV in orbit. Instead put a mirror and a lens in orbit. The lens will focus the sunlight to a point on the earth where the PV will convert it 24/7 to electric. I would use a focal length of 20,000 km for the lens. This will mean it will not be overly hot on the PV. The lens can be made of nitrogen gas held between to thin sheets of plastic with the correct radius of curvature. The mirror directs the sunlight to the lens/PV. The mirror is a thin aluminized plastic sheet.

Nitrogen with an index of refraction of 1.0003 works well for this application.



So in other words put a large magnifying glass in geostationary orbit, exactly like kids frying ants or a "solar concentrator". I imagine this would have a significant effect on temperatures as the column of air the beam transits is heated by the extra light...which generates wind and, if large enough, disrupts weather patterns.


Not only that, but clouds would at times greatly attenuate the concentrated beam. The beam could even be significantly refracted by varying atmospheric temperatures thereby causing other problems.

Cartoonists could have a field day with some of the things proposed here. They are about as innovative as some of Rube Goldberg's ideas.


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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 6:28 pm 
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Not a lot of clouds in southern Nevada.

Yes, sunlight at normal intensity will heat air and cause updrafts. People will be able to hand glide using them.


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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 7:22 pm 
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edpell wrote:
Not a lot of clouds in southern Nevada.

Yes, sunlight at normal intensity will heat air and cause updrafts. People will be able to hand glide using them.

Infinitesimal thermal effects will cause infinitesimal pressure effects that will totally change the focal point over that long a range. Using such a lens over a much shorter range on an orbiting PV array may buy you something.

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 Post subject: Re: Space Solar Power
PostPosted: May 07, 2014 8:11 pm 
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The first 35780km has zero air. It is only the last 6km that has air. If we get a 1% beam bending over 6km that is 60m which is fine for a 1000m installation.


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 Post subject: Re: Space Solar Power
PostPosted: May 08, 2014 1:19 am 
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edpell wrote:
The first 35780km has zero air. It is only the last 6km that has air. If we get a 1% beam bending over 6km that is 60m which is fine for a 1000m installation.
But if the lens gets thicker with pressure, the beam will spread over that 35780km you mentioned, not 6.

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 Post subject: Re: Space Solar Power
PostPosted: May 08, 2014 12:22 pm 
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KitemanSA wrote:
But if the lens gets thicker with pressure, the beam will spread over that 35780km you mentioned, not 6.


? The lens is in GEO orbit at 35786km in the vacuum of space. There will be no pressure change.


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 Post subject: Re: Space Solar Power
PostPosted: May 08, 2014 12:35 pm 
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Will the lens in orbit absorb any heat from incoming solar radiation which it's designed to reflect? Presumably yes. Are there (giant) controllable heat-sinks on the thing, or some other way to manage slightly changing conditions of solar radiation? I don't know if this is a problem, but it seems like it could be.


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 Post subject: Re: Space Solar Power
PostPosted: May 08, 2014 1:45 pm 
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If the idea of a lens made of gas is unappealing then think of a standard glass lens at GEO.


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 Post subject: Re: Space Solar Power
PostPosted: May 11, 2014 10:08 pm 
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edpell wrote:
KitemanSA wrote:
But if the lens gets thicker with pressure, the beam will spread over that 35780km you mentioned, not 6.


? The lens is in GEO orbit at 35786km in the vacuum of space. There will be no pressure change.
The lens will be rotating under the sun. The varying heat from the sun will cause varying temperatures and thus varying pressures. Good luck holding focus.

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 Post subject: Re: Space Solar Power
PostPosted: May 11, 2014 10:11 pm 
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edpell wrote:
If the idea of a lens made of gas is unappealing then think of a standard glass lens at GEO.
Micro-fresnel, maybe. But that problem would be to prevent warpage due to varying light pressure. I still think active phased microwave array is the simplest way to go.

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 Post subject: Re: Space Solar Power
PostPosted: May 11, 2014 11:24 pm 
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Location: Iowa, USA
I was reading a few articles recently about the growing concern over tracking the junk in orbit and the damage they can do to operational satellites. Certain orbits are safer that others. GEO sounds relatively safe but some inconsiderate behavior by other nations has left plenty of junk in that orbit. Currently the issue is dealt with by armoring satellites, evasive maneuvers when big chunks get in the way, and just dumb luck.

Probabilities are on the side of small satellites, less area for critical parts means less chance of something getting damaged. A solar array that is a kilometer wide is not a small target. Solar panels cannot be armored like other devices since it must be able to collect light from the sun. Some holes in a solar panel can be tolerated, perhaps beneficial if it destroys a sub par cell that was sinking current rather than sourcing it. A piece of debris from another satellite can collide with the panel or antenna array and break off pieces, making more debris.

Perhaps my concern is unfounded, perhaps I misunderstood or was given poor information. I just feel the issue of orbital debris needs some mention in the discussion of orbital solar panels since standard methods of addressing the debris problem are incompatible with collecting solar energy with light and thin solar cells and transmitting that energy with a high power antenna array that, because of the laws of physics, must have a size on the order of a kilometer.

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 Post subject: Re: Space Solar Power
PostPosted: May 11, 2014 11:48 pm 
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You could, at relatively low weight addition, coat the non generating side of the PV array with "whipple shielding" which will tend to sink particles rather than generate them - which should turn the array into a net reducer of debris.


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 Post subject: Re: Space Solar Power
PostPosted: May 12, 2014 10:59 am 
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E Ireland wrote:
The only way you can ever get space solar down to a reasonable cost is space based fabrication of components from lunar or asteroidal material.
Lifting something up the well just costs far too much.


That's pretty much what i said when this topic first came up.

Except, you can't cover the initial cost of a good asteroid or lunar base. And you need to (or should) start at GW scale to make the rectennas/receiver combination work.

If or when humanity becomes a space faring nation, then you have your base, and you have your low cost solar power, and you have SSP.

Low cost: Kirk's statement about not closing the business case at zero launch cost was based on the cost of solar 20 years ago. It's a lot cheaper today and will be even cheaper to make in space (with the right infrastructure). Why? Consider a 1km wide solar cell "printer", printing cells onto aluminium foil, in situ. So almost no transport costs compared with getting your heavy aluminium and glass structure onto some guys roof.

Trouble is, no one knows when humanity will become space-faring. Hopefully before the next scheduled major asteroid impact.


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