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Offline Freeholder

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electricity generation in earth orbit
« on: 13/03/2007 02:37:13 »
If an electrical engineer could respond to this question, I would be glad.

 Here it is. I know electricity is "made" be the very fast movement of conducting wire in a magnetic field.  Water power or steam can be made to spin vast lengths of wire in the magnetic field of powerful magnets. These dyanmos are connected to power lines and eventually to our houses.  (I have to leave off the step-up and step-down "magic" of transformers because I don't know how volts, watts, amps and so on are sort of interchangable. )
 
Just the same, here is the question: Can electricity be made in space in enough energy to power all the needs of the international space station?   And here the theory meets the practical. 
 
Since this planet exudes a vast magnetic field that extends out to the space station and beyond, and since the space station is whirling around at the same speed as the planet spins, (isn't the turning speed of the planet something like 24,000 miles per hour), it would seem to be practical to extend long lengths of wires out from the space station into the magnetic field and harvest electricity!
 
I read some years ago of an Italian physicist who tested this theory by doing just that: Extended a wire antenna out from the space station, and sure enough it generated  electricity.Then there was a sort of caveat mentioning the tendency of the wire to coil up, or otherwise make trouble. Then the experiement dropped out of the news.
 
If the cosmo-astronauts could make their own electricity on site, that should recharge batteries and eliminate the need for fuel cells (which are environmentelly unsound anyway, since those cells need more enectricity to get charged up then they save.)
 
So do any electricity mavens read these posts?  If one does, how about posting an answer?


 

another_someone

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electricity generation in earth orbit
« Reply #1 on: 13/03/2007 03:32:57 »
Firstly, as far as I am aware, the ISS is not in geostationary orbit.  This is not of major significance to the question, merely a minor detail.

Secondly, as you point out with the experiment from the space shuttle, yes it is possible to generate electricity through a very, very, long wire strung out from a space craft across the earth's magnetic field; but it actually is not required, since it is easier to generate the electricity from solar panels.

As far as I am aware, fuel cells are only used in the spacecraft used to transport the astronauts into, and down from, space; and this is because those vehicles need to be more compact, and cannot have bits sticking out of them as the climb out of, or descend through, the atmosphere.  This is not a limitation on the ISS itself.
 

Offline Soul Surfer

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electricity generation in earth orbit
« Reply #2 on: 14/03/2007 19:16:45 »
There was an experiment in space using a long conducting wire from a satellite but they made some sort of mistake and the cable burned out due to excessive current so it does seem that it is possible to generate power from a conducting wire moving in the earth's magnetic field.
 

Offline lightarrow

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Offline that mad man

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electricity generation in earth orbit
« Reply #4 on: 21/03/2007 21:45:12 »
This has got me puzzled after reading the 2 links by lightarrow.

To generate electricity by the magnet principle the magnets poles have to rotate end over end as its the poles that count.

If you take the earth as a simple bar magnet then the poles are static and the equator spins so any thing in space would have to travel over the poles to generate electricity.

The space station is in geostationary orbit and relative to the earth it don't move.
 
TMM
 

another_someone

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electricity generation in earth orbit
« Reply #5 on: 21/03/2007 22:58:31 »
This has got me puzzled after reading the 2 links by lightarrow.

To generate electricity by the magnet principle the magnets poles have to rotate end over end as its the poles that count.

If you take the earth as a simple bar magnet then the poles are static and the equator spins so any thing in space would have to travel over the poles to generate electricity.

The space station is in geostationary orbit and relative to the earth it don't move.
 
TMM

Not sure that this is true - just look at a homopolar generator.
 

Offline that mad man

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electricity generation in earth orbit
« Reply #6 on: 22/03/2007 18:40:36 »
Hi another_someone.

Yes you are correct, it is not strictly true but homopolar generators are very inefficient and provide just a low voltage at a great ampage. Not a very practical way to generate electricity as its very inefficient and thus rarely used.

But, to generate electricity in space the magnetic lines of flux of the earth have to be crossed, normally at right angles as being in parallel to them would give little or no output. Its the normal generator principal.

I think I got it wrong about the space station, for some strange reason I thought it was in geostationary orbit.  [:I]

TMM
 

Offline thebrain13

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electricity generation in earth orbit
« Reply #7 on: 07/04/2007 19:24:55 »
the generation of the electrical energy would be made at the exspense of the earths angular momentum right? and would it affect the spacestations?
 

Offline Batroost

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electricity generation in earth orbit
« Reply #8 on: 14/04/2007 09:39:58 »
Two things:

(1) The ISS is in low earth orbit (currently around 320 km up, at 27,800 kph) and so travels around the globe ~16 times per day. As the Earth's Magnetic field is effectively stationary with respect to the earth's surface, the ISS is moving through this field continuously.

(2) You don't get something for nothing? Wouldn't any current induced in a trailing wire also produce a braking force on the ISS i.e. slowing it down?
 

Offline that mad man

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electricity generation in earth orbit
« Reply #9 on: 14/04/2007 18:21:42 »
Thanks Batroost.

I look forward to a real test of a tether satellite as its all new stuff but for normal electrical generation it should work like the following.

(1)
Imagine the earth as a magnet and the ISS the coil. The same principle applies as in normal electrical generation in that the coil has to pass over or close to the poles to produce anything.

Take a bar magnet and place a coil nearby half way down the magnet. Now spin the magnet on its axis and check the coil output with a meter, no output. In that position the magnetic lines appear to be static and do not rotate even though the magnet rotates.

Suspend the magnet by some thread from its middle and now rotate near the coil. As each pole is now rotating near the coil there will be an output.

I believe it is one of Faradays laws.

Sorry about the primitive diagram. C=coil M=meter

The spinning magnet on the left produces nothing and has no effect on the coil. It also has no effect on another magnet (other than attraction) placed in a similar fashion below it.

The spinning magnet on the right however, will produce an output in the coil.






(2) The ISS is affected by some residual earth atmosphere so I would think that friction on the wire (assuming there would be one) would cause a slight drag.

TMM
 

Offline Batroost

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electricity generation in earth orbit
« Reply #10 on: 14/04/2007 23:48:36 »
And another thought... the orbit of the ISS is inclined at around 50 degrees to the equator. So although it doesn't reach the magnetic poles there is a significant N/S component to its motion.
 

Offline that mad man

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electricity generation in earth orbit
« Reply #11 on: 15/04/2007 22:28:50 »
Yes Batroost there is a N/S component but the frequency in which it crosses is slow.

If you consider an electrical generator then turning it one revolution every 90min will produce almost nothing. It has to be a rapid rotation around the poles to produce any usable output.

With a tether or trailing wire I don't know but, I think the Sun's discharge could cause an electron flow in a wire in space that was above the Earth's atmosphere.
Possibly just a loop as it would need a closed circuit to work.

Interesting stuff though.  :)

Bee




 

Offline Batroost

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electricity generation in earth orbit
« Reply #12 on: 15/04/2007 22:44:40 »
Slow rotation would give low voltage/frequency but a long wire might still produce a usable current, say enough to power a small satellite? On the other hand the Earth's magnetic field is pretty weak compared with most electrical generators.

Would the Sun's Electrical/Magnetic effects be strong enough inside the Earth's manegtospehere i.e. if the Earth's mangetic field is strong enough to deflect a significant fraction of the solar wind away from the Earth (except at the poles, hence aurora?) then I doubt what's left is going to be of help?

[Not my field - so some guessowkr here].
 

paul.fr

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electricity generation in earth orbit
« Reply #13 on: 16/04/2007 09:29:05 »
if i remember correctly, NASA have already tried generating electricity in a similar way, the cost of materials far outweigh the benefit of what little energy they produced.

there must be some info on this somewhere on the NASA website: www.nasa.gov
 

Offline that mad man

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electricity generation in earth orbit
« Reply #14 on: 20/04/2007 16:37:09 »
Had a good look but cant find out much more.

Conditions seem to change depending on where you are in respect to the earth. It seem that at some altitudes there is also a plasma effect to take into account.

If a trailing tether wire can produced many amps but little voltage it could be used like a arc welder and burn a lightweight metal. That could then be used for propulsion, maybe!

Bee
 

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electricity generation in earth orbit
« Reply #14 on: 20/04/2007 16:37:09 »

 

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