# Using a satelite to make power ?

i just went over this in physics, but if you take a coil, and pass a magnet near it (without touching), you create an emf while you come near it and when you leave. i believe its the Faraday effect/observation/whatever?

but with that in mind, i had this idea: if you take some really big coils and put them in space so the orbit the earth say counterclockwise, and then take a big magnet and make it orbit the earth clockwise, and some how hook it all up so that you when the current flows from the coils you say charge a really big battery or something. isnt that essentially free energy?

now i understand that most probably the satelite will fall because of the loss in energy, but if you position you coils just right, you could have it bounce sort of every time it passes through one, and maybe once every decade or so prop them up a bit? it sounds really insane but i just thought it might potentially work... any ideas?

russ_watters
Mentor
If its orbit decays (and it would), then it isn't free energy.

Yes, the orbit will shrink.... and the amount of its shrink (decrease of gravitational potential) is exactly equal to the EMF its gains from the magnetic field.... therefore, the energy isn't free, it has a price to pay....
One more thing to notice, the magnetic field of the earth is weak, the energy extracted from the field is very small unless the satelite carries a HUGE COIL.... If you just wanna power up a satelite, the best way (and what we are already doing) is used the solar power.... it is FREE..

i guess... it justed seemed like a funny idea at the time.

vincentchan said:
Yes, the orbit will shrink.... and the amount of its shrink (decrease of gravitational potential) is exactly equal to the EMF its gains from the magnetic field.... therefore, the energy isn't free, it has a price to pay....
One more thing to notice, the magnetic field of the earth is weak, the energy extracted from the field is very small unless the satelite carries a HUGE COIL.... If you just wanna power up a satelite, the best way (and what we are already doing) is used the solar power.... it is FREE..
Nice name! Vincent Chan is my name too :rofl:

I used to wonder about the same thing. Now I have a question.. What if humans are capable of creating some humongous halo-shaped structure around the planet with one layer of the halo spinning in one direction, and the other layer of the halo spinning the other direction? Energy required to spin the halo can be supplied by solar power, but because there is hardly any friction in space, the movement of the halo will be driven mainly by momentum. This halo is in turn "orbiting" around earth, but the orbit will never decay because it is supported by every other part of the halo. Will such a concept work to generate "free energy"?

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russ_watters
Mentor
Whenever you use magnets to produce electricity, the primary force you have to contend with is magnetic. Friction is insignificant even in commercial generators. These "halos" will slow down without a constant input of energy.

as far as i see it, a machine that "creates" energy from nothing is impossible UNLESS you manage to "harness" the power of something mundane, and essentially convert back lost energy into useable energy with little work involved on your side. like if you were to say somehow convert all the heat of friction from the roads into battery power, there would be a lot and it would seem to be "free", but it really isnt. i just chose a satelite because it moves more or less without anyone pushing it (once its up).

maybe im wrong about this, actually as i write im getting doubts. wouldnt the energy it takes to convert the useless heat be equal to the amount you get out (idealy)? ok im confused now. can anyone explain this?

DaveC426913
Gold Member
take a coil, and pass a magnet near it (without touching), you create an emf while you come near it and when you leave.

It takes energy to push your way through the field - which will resist. You're not getting free energy, you're converting mechanical energy of motion into electromagtnetic energy

vcc said:
This halo is in turn "orbiting" around earth, but the orbit will never decay because it is supported by every other part of the halo. Will such a concept work to generate "free energy"?

So what will happen is that the resistive forces imparted by the magnetic interaction will cause the halos to decelerate until they are at rest.

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russ_watters
Mentor
maybe im wrong about this, actually as i write im getting doubts. wouldnt the energy it takes to convert the useless heat be equal to the amount you get out (idealy)? ok im confused now. can anyone explain this?
I'm not sure what "useless heat" you are talking about, but consider a hydroelectric dam. In a hydroelectric dam, there is a certain quantity of water at a certain potential energy (height above the river below). Before the dam is built, this is all just unused energy. The water splashes down waterfalls and such and generates a little heat, but does't really do anything. Converting this potential energy into mechanical kinetic energy (rotation of the turbines) and then into electric power requires no input energy except for the power to run the computers in the control room and a few lights in the turbine room (which is an absolutely trivial amount). What you do have is losses due to friction and electrical inefficiency (in the generators and transformers), but that's an essentially flat percentage of your output (typically ~10%).

There is no fundamental difference between the potential energy of the water in the dam and the energy in any random heat source, such as a boiler: all you have to do is find an energy/heat source (the dam or a boiler) and sink (the river or the atmosphere), set up a system where the heat flows from the source to the sink (that's the purpose of a steam engine) and stick a generator in between.

That's thermodynamics in a nutshell.

edit: One note - while this satellite idea is a thermodynamic engine, photovoltaics are not. Thermodynamics involves heat (kinetic) energy, photovoltaics convert directly from radiant to electrical.

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speaking of hydroelectic dams. What contributes more to increased electricity? Dynamo speed? or Dynamo size?

(for example.. building a dynamo 2X larger, or building a dynamo that goes 2X faster)

ok thanks russ_watters i get it now. but if you were to compare the dam idea to the satelite one, the satelite is falling (sort of like the water) and the coil is like your turbine... i guess the difference is that the water cant be "pushed down" away from the turbine since it already is...
speaking theoretically now, if you were to take a say 2 meter diameter spherical satelite and the coil is has a radius say 2, how much power would you expect to get?
(i know there more, like how much it wraps around and stuff, but just pick a random number that seems right if you come to thsi problem)

BobG
Homework Helper
i just went over this in physics, but if you take a coil, and pass a magnet near it (without touching), you create an emf while you come near it and when you leave. i believe its the Faraday effect/observation/whatever?

but with that in mind, i had this idea: if you take some really big coils and put them in space so the orbit the earth say counterclockwise, and then take a big magnet and make it orbit the earth clockwise, and some how hook it all up so that you when the current flows from the coils you say charge a really big battery or something. isnt that essentially free energy?

now i understand that most probably the satelite will fall because of the loss in energy, but if you position you coils just right, you could have it bounce sort of every time it passes through one, and maybe once every decade or so prop them up a bit? it sounds really insane but i just thought it might potentially work... any ideas?
I'm not sure what your point is. Is your intent to generate electrical energy using electromagnetic coils, or is your intent to find some use for the magnetic field?

If the second, it's more effective to reverse the process. Your electrical energy is essentially free (at least to you) since it comes from solar energy. Use your electricity to create a magnet. If you turn on your electromagnet, the magnet's magnetic field will try to align itself with the Earth, causing the satellite to rotate with the magnet.

If the Earth's magnetic field were aligned perfectly with the Earth's rotational axis (it isn't), you'd have a 'free' way to keep your satellite pointed at the Earth (provided your altitude is relatively low - the strength of the magnetic field tapers off pretty quickly). Considering you can't easily refuel a satellite, that would be a huge improvement over using thrusters to point your satellite. Unfortunately, the Earth's magnetic field isn't aligned with it's rotational axis.

Electromagnets can still be a huge asset on a satellite. Consider the fact that the atmophere doesn't abruptly end at some arbitrary boundary. Satellites below 1000km (around 600 miles) in altitude still encounter some atmosphere, even if very thin (above 1000km, the atmosphere is so thin that you could disregard it unless your satellite had an extremely high area to mass ratio - like Echo I, the first artifical communication satellite, which was basically a balloon with a reflective coating).

If you slap a humongous solar array on the side of your satellite, it's constantly being slowed by the atmosphere, causing your satellite to slew to one side (solar arrays also have a high area to mass ratio). You can compensate for that torque by spinning a wheel inside the satellite to create an opposite torque. Unfortunately, it's the change in wheel speed that compensates for the torque, not the actual wheel speed. Since the torque occurs constantly, your wheel has to accelerate forever. Your wheel can only spin so fast. Eventually you have to slow it down if you want to keep on using it to counter the torque from the solar array dragging through the atmosphere. You can fire a thruster to create an opposite torque, forcing your wheel to slow down (that's called a momentum dump), but you lose that capability once you run out of fuel.

Better is to use your electromagnet. If you turn on your electromagnet, the satellite will try to align itself with the Earth's magnetic field. This will put a torque on your satellite that you have to compensate for by changing the speed of your spinning wheel. If you turn your electromagnet on at the right time, the torque caused by the magnet trying to align itself with the Earth's magnetic field is opposite the torque caused by the solar array. In other words, the wheel slows down to compensate for the torque caused by the electromagnet and you don't have to use any fuel (polar orbiting weather satellites can last 5 years or more and may never fire their thrusters after they're stabilized in their orbit shortly after launch).

thanks for the reply bobg, to clarify i guess my point was to create a bettery that never runs out, but you said that solar is free anyway, so i guess i was thinking of like a free battery that is *much* stronger than a solar battery.

sorry right now i really dont have time to go over your reply, ill get back to you when i do :)

hmmm i read it fully now, and i see what you mean. but im not sure i agree, is electricity really free? i mean if you could create a humongous battery for very little, i guess it would help in alot of things. but then i never ran the numbers so i have no idea how strong solar power is to it. thanks though :)

BobG
Homework Helper
hmmm i read it fully now, and i see what you mean. but im not sure i agree, is electricity really free? i mean if you could create a humongous battery for very little, i guess it would help in alot of things. but then i never ran the numbers so i have no idea how strong solar power is to it. thanks though :)
In the vicinity of Earth, you get about 1400 Watts per square meter of solar power. Unfortunately, solar panels aren't very efficient at turning that into electricity. The best operational solar panels (gallium arsenide) get around 20% efficiency while the older silicon solar panels get around 10%. The panels degrade over time, so you have to use the end of life efficiency vs. the 'best' efficiency - that means the actual efficiency depends on how long your satellite is expected to live.

Launch weight is the real cost of spacecraft, so the high area to mass ratio of solar panels makes them the best investment using current technology.

i see. obviously you know far more than me about this so thanks for the help. appreciate it :)

Why not suspend small satellite from long wire,this way when satellite cuts thru earth magnetic field it will generate electricity.

the wire would have to be *very* strong. if you mean a wire all the way from the earth, then i think at least no such material exists that can hold the satelite there and not break. and it would have to rotate on the earth as well, which would be this huge gargantum project involving many nations = no.

I mean wire between let's say shuttle and satellite, or space station 1000m long for example.It will generate some electric current all the time.

see i think that might work, only thing is that there are probably like 200 better ways, so sure, you make current, only its probably easier in like a jillion other ways.

see i think that might work, only thing is that there are probably like 200 better ways

I know one can get juice from solar, nuclur, some form of chemical thingy stuff.But with the wires stiking out it is gonna be much more cheaper i guess.
I'm done man.

i dont understand much about whats going on in this topic but i read in popular science that there are plans for a carbon fiber evelvator into space. It would be mircons thick or something but super strong.

meep im done on this subject. very probably. really i honestly have no idea anymore :) i give up lol

Someone502 said:
i dont understand much about whats going on in this topic but i read in popular science that there are plans for a carbon fiber evelvator into space. It would be mircons thick or something but super strong.

They must invent some anti-gravity thing, no need for rockets and stuff.