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Possible alternative way to generate electricity in space?

Posted by: Ekkehard Augustin - Mon Feb 21, 2005 11:58 am
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Possible alternative way to generate electricity in space? 
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Post Possible alternative way to generate electricity in space?   Posted on: Mon Feb 21, 2005 11:58 am
It's only a curious idea of this moment - but there are elements for normal generators in space perhaps.

There are many small asteroids set to fast rotation by sunlight - no steam, water or something else required to cause the rotation.

So on the surface of some of the asteroids magnets could be installed.

The rotating asteroids could be surrounded artificially by a wire. This should cause electricity in principle.

You can laugh at it, call it silly or stupid or the like - but it would be interesting how strong the magnets would have to be and what would be required regarding the wire - length, material and so on.



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Post    Posted on: Mon Feb 21, 2005 6:03 pm
You have to prevent the wire from rotating with you. That could be a fairly high energy expeniture.

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Post    Posted on: Mon Feb 21, 2005 6:29 pm
Yep, that would be a fairly big problem to avoid. The asteroid itself would also have its own irregular gravitational forces that would pull unevenly upon the wire grid, causing further placement difficulties (weak forces, yes, but I'd imagine that they'd still be significant when it comes to this application).

What, though, if a more abstract application were tried?

If a fairly perfectly spherical object were to be created, being magnetically polarized, and placed withing a spherical wire-grid shell in space. With negligable air friction, the main problem seems to be maintaining the sphere's translational orientation at the centre of the wire shell. This would likely involve moving relatively far from a gravitationally charged body and placing the sphere at the centre of the wire shell (difficult). The sphere could be initially held in place by a network of screws, each controlled by servos that were operated in an even and controlled manner to free the sphere without applying unequal force on it. A spin in the sphere could then be induced by initially applying alternating current across the grid.

After this, if the sphere/wire/housing contraption were left alone to be equally affected by gravitational forces, and the produced energy were to be beamed out to another location, then this form of generating power, though high in maintenance for maintaining the relative location of the sphere/grid, may be productive.

A major problem, though, I admit, would be this 'beaming' of power, which would be a form of propulsion in itself.


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Post    Posted on: Tue Feb 22, 2005 5:08 pm
I have been thinking about your problem too, idiom, and also about an artificial object.

In the case of the asteroid the poles have to be found. Then from each pole an axis would have to be built. The axises would be fixed on the ground Then a construction that holds the wire is to be set to the axises. Where the construction is sitting on the axises magnets should be used to avoid direct touch of the axises to the construction.

By one impulse the construction could be given a velocity that is different to the velocity the asteroid is rotating by. A small asteroid of a size of a few meters only would be sufficient - for an experiment at least. The asteroid's shape could be improved artificially perhaps.

All this could be apllied to a totally artificial object. I'm sorry - I didn't find time yet to read the ideas already posted since yesterday. So the following short idea may have been included there already: The body of the object could be set to rotation by small solar sails that can be impacted by light at one side only.

What ideas else could be imagined?

To add a remark - this could be interesting at distances from sun larger than that of Mars because the sunlight is so weak there that it cannot be used directly to get sufficient electricity but by magnets and wires this could be possible I suppose. ...



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Post    Posted on: Tue Feb 22, 2005 7:21 pm
So, the sun hitting the sails would counteract whatever frictional forces there would exist at the junction between the axis and the grid. Well, it seems that all that's left is to try it and see which produces greater energy production: solar cells or a photon vs. friction AC generator.


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Post    Posted on: Wed Feb 23, 2005 2:46 am
The problem is getting more enrgy out of rotation than you put in.

In space generators have to be driven at both ends, on Earth on end has torque applied by the earth itself.

Solution: Two counter-rotating solar windmills. The generator is on the axis between them. The near side has a large regular windmill and the farside has a much bigger donut shaped windmill sized to create the same amount of torque as the near side. The would resemble really shiny sunflowers...

A Solar-Sunflower™

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Post    Posted on: Wed Feb 23, 2005 10:55 am
I seem to have to add a detail - the magnets installed on the surface of the asteroid as well as the magnets that prevent touch between the axises and the consturction for the wire should be permanent magnets but not electromagnets.

If this is possible no energy would be required for magnetization. Perhaps sunlight and solar wind could add assistance.

The impulse to set the construction for the wire to movement could be got by sunlight: Imagine the axises being horizontal. Then that side of the object-sided solar sail that can be impated by sunlight should be below the axises and the identical side of the construction-sided solar sail should be above those axises. Then both components would be counterrotating by sunlight only. Given the permanent magnets no artificially generated energy would go into the production process - it would be similar to a water powered generator or a tidal generator as has been concepted for the region where the Elbe flows into the North Sea.



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Post    Posted on: Thu Feb 24, 2005 2:10 am
Idiom,
Interesting idea,...
What would maintain the orientation of the 'sunflower' aparatus with respect to the light source? I can see how having the torques theoretically balance could nulify frictional concerns (though that would be a very difficult egg to crack in reality, I think), but the aparatus will be "blown" around a bit by solar wind. It can't be anchored to an asteroid, as the asteroid would be rotating itself.

Ekkehard,

It sounds as it you're in for magnetic-field problems (effects between the two/three fields). Without having electromagnets involved (admittedly a counter-productive component, as it would consume energy), how would the system be fine-tuned so as to remain functional for any significant period of time? Creating a detailed enough model of the asteroid/grid system that the strong magnets may be pre-fabricated to ammount to the perfect strengths seems to be difficult, at best. Remember the KISS principle. I'd imagine that considerably more energy would be invested in creating such a system that would likely need frequent adjustments in the future to remain productive.


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Post    Posted on: Thu Feb 24, 2005 7:22 am
By its nature it would have pretty intense gyrosopic forces.

It would need a station keeping system as well as energy transmission systems positioned at the end of a long central 'stalk' facing away from the Sun. The stalk would need to be attached using a frictionless magnetic bearing system right through the collar of the generator.

The greatest difficulty is reducing the sail effect. If the stalk had a huge mass then the forces on the blades would be insufficent to push it much at all. If it was initially placed at a low orbit (~Venutian) it would be obsolete or malfunctioning by the time it had gotten anywhere.

The blades would have to gargantuan though...

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Post    Posted on: Thu Feb 24, 2005 10:43 am
Hello, slycker,

I don't have the knowledges required to think about fine-tuning and would like some explanation of you concerning the reasons for fine-tuning and so on.

When I first had the idea I din't have in mind to cover the whole asteroid with magnets. This is valid for the artificial object too. I had in mind one line of magnets along the equator of the asteroid or the object only.

Asteroid or object - it doesn't need to be a globe - it could be cylindric with equatorial diameter small compared to polar diameter.

"line" combined too large polar diameter - could that avoid problems or help to avoid them at least?

Are elctormagnets involved in normal earthian electricity generators where steam. water and the like drive the turbines?



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Post    Posted on: Thu Feb 24, 2005 5:54 pm
Hmm.
Using an asteroid's mass and rotation to turn one half of a generator is a nifty idea. But, as stated, preventing the other half of the generator from starting to rotate is at least fairly difficult.

I have a somewhat different idea. I'm assuming this is for a space colony, asteroid settlement or something similar. Therefore, there should be some form of onsite maintainance or periodic visit possible. How about using a parabolic mirror to heat a boiler. You then use the boiler's working fluid to heat one or more stirling engines. This is less efficient than having the mirror directly heat an engine but allows you to put the engine(s) in a pressurized hull, so mechanics don't have to wear spacesuits quite as often. After powering the engine(s) the fluid would be pumped to radiator fins behind the mirror, or into an asteroid, to cool off. Done right you could probably use water as the working fluid. If you want to you can even run the working fluid through a heat exchanger to help warm the habitat's fish or pond scum tanks.

Commentary is very welcome.

Cheers,
ErikM :twisted:


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Post    Posted on: Thu Feb 24, 2005 8:03 pm
I had to look this one up to figure it out:

http://www.stirlingengine.com/

http://travel.howstuffworks.com/stirling-engine.htm

http://www.bekkoame.ne.jp/~khirata/english/struct.htm

basically, if anyone else out there had no idea what a stirling engine was, it is an engine that runs off of a temperature differential. The stirling engine produces mechanical rotation, which may then be coupled to a generator.

While I'm not sure what the obtainable horsepower from the massive temperature differential that would exist in this application, but it is fairly easy to imagine that a suitably scaled-up version would produce enough torque to overcome any frictional costs in generation of electrical power.


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Post    Posted on: Fri Feb 25, 2005 7:40 am
Hello, slycker,

for waht reason one half of the generator has to be prevented from rotating? Can't one half rotate to the opposite direction the other is rotating to?



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Post    Posted on: Fri Feb 25, 2005 1:48 pm
That's one reason I like Stirling Engines: park one in a reasonably close orbit around the Sun. You get a truly insane temperature differential that way -- imagine a cloud of Stirling Engines chugging away like Watt's old steam engines.

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Post    Posted on: Fri Feb 25, 2005 4:38 pm
Quote:
for waht reason one half of the generator has to be prevented from rotating? Can't one half rotate to the opposite direction the other is rotating to?


It's not so much that one side has to be prevented from rotating as that there has to be an RPM difference between both sides. This difference has a fairly tight tolerance and letting the difference go up or down too much generally causes bad things to happen to anything connected to it (due to voltage and frequency fluctuations). Building a generator is generally done by bolting one side (the stator) to the floor and letting the floor absorb the torque and gyroscopic forces while the other side (the rotor, to which the axle is attached) spins inside the stator's magnets. When I say 'half' a generator I am talking rotor/stator, not about percentages of mass.

A generator with a rotor spinning inside a counterrotating stator could be possible, but the mechanical linkages involved would probably be quite nightmarish. Additionally, the gyroscopic forces generated by spinning the stator would be larger than spinning the rotor inside a stationary stator.

Unfortunately, bolting an engine/generator set to a space station's structure can cause several bad things to happen. Potentially, a single set could cause the entire station to start tumbling, causing no end of trouble (let's start with docking alignment). Running several counterrotating sets should balance out most effects and provide power redundancy to boot. As a bonus, this should help out a bit with attitude keeping.

One other thought. If you use a stirling engine as driving engine you will probably actually have to have two sets of radiators. One set cools the primary working fluid (the hot side of the engine) and the other cools the cold side of the engine. The working of both should be roughly analog to that of a refrigerator.

As a bonus, http://www.spacedaily.com/news/energy-tech-04zzzc.html is more or less what I'm talking about, except in terrestrial use. Stirling engines are apparently already being used in non-nuclear Air Independent Propulsion systems for submarines.

Commentary is welcome!

Cheers,
ErikM :twisted:


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