Space Power Generation

[KASASpace]

I was thinking:

What if, as a spacecraft, you had a generator, with the magnetic field in such a way that it rotates with an axle.

This axle got started rotating by RCS thrusters on booms out to the side of the axle itself.

Would this setup generate power?

And if so, how much would the maximum be?

I bring this up because the primary reason we can't do this in atmosphere is the air friction stops the booms from rotating.

Also, the contact with other surfaces is limited (and the surfaces are heavily polished at that).

[mrfox]

The magnetic field will apply a torque to the spacecraft (and vice versa), and eventually both will end up rotating at the pretty much the same speed.

The amount of power generated will equal the impulse applied by the thrusters, minus the momentum gained by the spacecraft from the axle, minus losses.

The first law of thermo always applies.

[Red Iron Crown]

More efficient to have the RCS drive a turbine, I would think. Turbines are about as efficient as it gets for turning thermal energy into rotational mechanical energy.

[Sillychris]

It would generate power, totally. And the axle would lose at least as much angular kinetic energy as electrical energy it produced. So unless you kept feeding rcs thrust, it would slow down and stop.

[KASASpace]

The magnetic field will apply a torque to the spacecraft (and vice versa), and eventually both will end up rotating at the pretty much the same speed.

Hmm, that I will have to read up about.

But, you could have two of these systems facing each other, and as such you can counter the majority of the torque, or at least some of it.

[K^2]

No, you can't. You are trying to invent a perpetual motion device. Energy has to come from somewhere.

[KASASpace]

No, you can't. You are trying to invent a perpetual motion device. Energy has to come from somewhere.

I'm not saying it's perpetual, I'm saying you can counter some of the torque and increase the operational life before having to burn again to increase the spin rate once again.

[TheDarkStar]

This would basically convert RCS fuel into electricity. However, it would stop fairly soon after you stopped giving it fuel, since it takes some energy to generate the rotational force (which mostly becomes electricity), as I understand it. Really, if you wanted a similar set-up to generate power, you'd use the most efficient engine you had that did not use huge amounts of electricity (so no ion drives) to keep it going for a long time.

Edit: Good point about them eventually rotating at the same rate, but what happens if you continually use more RCS? Would it get faster and faster, or would it stay constant (It's late right now and I can't think clearly enough to figure it out).

Edited April 18, 2014 by TheDarkStar

[mrfox]

Hmm, that I will have to read up about.

But, you could have two of these systems facing each other, and as such you can counter the majority of the torque, or at least some of it.

Then the system will come to rest.

The torque is where you are getting the electricity from.

Think of it this way - If you are to make a rotating space-station, using a electric motor in the hub, would it require power to spin up?

A generator is just a motor in reverse.

[mrfox]

I bring this up because the primary reason we can't do this in atmosphere is the air friction stops the booms from rotating.

Also, the contact with other surfaces is limited (and the surfaces are heavily polished at that).

Your premise is wrong. The primary thing that eventually stops the booms from rotating, in or out of atmosphere, is the torque from the the magnetic field.

[Seret]

It would work fine if you had opposing sets of RCS thrusters. You'd just be converting monopropellant to electricity at pretty low efficiency. Given the severe weight penalties that spacecraft operate under I don't think using mass to generate power is a great idea.

[KASASpace]

Then the system will come to rest.

The torque is where you are getting the electricity from.

Think of it this way - If you are to make a rotating space-station, using a electric motor in the hub, would it require power to spin up?

A generator is just a motor in reverse.

Wait, what do you see in your head when you read:

What if, as a spacecraft, you had a generator, with the magnetic field in such a way that it rotates with an axle.

This axle got started rotating by RCS thrusters on booms out to the side of the axle itself.

Because I don't think I explained it clearly enough.......

[Dodgey]

I see a generator. Which would come to rest as soon, or soon after, the mechanical force rotating or is removed. It is the magnetic force which brings a generator to rest. All you are doing is converting the RCS into rotational motion then into electrical energy.

[KASASpace]

I see a generator. Which would come to rest as soon, or soon after, the mechanical force rotating or is removed. It is the magnetic force which brings a generator to rest. All you are doing is converting the RCS into rotational motion then into electrical energy.

And what components would make up this generator?

A simple magnetic field rotating with wires within the field, all coiled up around it on the part of the machine that isn't moving?

[shynung]

And what components would make up this generator?

A simple magnetic field rotating with wires within the field, all coiled up around it on the part of the machine that isn't moving?

The axle is the rotor. The spacecraft, and with it the coiled wire, is the stator. A generator is comprised of a moving rotor and a stationary stator.

I think it's obvious from here.

[Dodgey]

The axle is the rotor. The spacecraft, and with it the coiled wire, is the stator. A generator is comprised of a moving rotor and a stationary stator.

I think it's obvious from here.

Pretty much, and this is without considering the size of the magnetic field required to make this work.

[Sillychris]

Because I don't think I explained it clearly enough.......

Could you explain it more clearly, then?

What I picture is a relative motion between wires and magnetic field. The relative motion is created by rcs, the relative motion induces an electric current and by Lenz's law the magnetic field induced by the current directly opposes the original magnetic field, leading to conservation of energy.

In the long run you are converting fuel to electricity, however you spin it.

Not too different from a coal burning power plant or gas powered electric generator (Fuel->spinning->electricity). I still thing solar panels or nuclear thermocouple devices are better choices for spacecraft.

[mrfox]

Wait, what do you see in your head when you read:

I see a rube goldberg machine.

Again, ask yourself this - thermodymically speaking, where is the energy coming from in this system, and to where and how is it flowing?

[KASASpace]

Not too different from a coal burning power plant or gas powered electric generator (Fuel->spinning->electricity). I still thing solar panels or nuclear thermocouple devices are better choices for spacecraft.

I never really said this was practical. I would just like to know, could this produce SOME power?

Hmm, what it is is a hollow cylinder, with a smaller rotating cylinder inside of it, which bears the magnetic field.

The hollow cylinder has the wires coiled up around the inside of it.

The rod, which is a better name for it, is attached to the rotating magnetic field and extends outward, where, at the end, it has a booms which have RCS thrusters, or some other form of thruster, firing to spin it up. Perhaps a great distance from the center, so less force would be needed to get it to the rod, and thus the magnetic field, rotating.

[Charzy]

Here's an interesting experiment for you to try. Get a magnet (preferably cylindrical) and a non-ferrous pipe (preferably of the same internal diameter as the magnet). Drop the magnet down. It will convert the gravity will convert the gravitational potential energy of the magnet into kinetic energy, which will then be converted into electrical energy which will be generated in the pipe.

This results in the magnet going down the pipe very, very slowly (this is not because it is attracted to the pipe, because the pipe isn't ferrous). This loss in speed is because the kinetic energy is being converted into electrical energy and so the magnet loses the kinetic energy and goes more slowly.

Your idea would certainly produce electricity, but what will end up happening is that the rotating bit will slow down unless you apply constant torque to the boom via the RCS, and it will rotate very, very slowly and not produce very much electricity.

[KASASpace]

Well there you go!

Although, if using a very long boom, not much burning would be needed to get to the same speed.

I know of ferrous material and how it magnetically attracts to "magnetite," as the Chinese called it.

Of course, Gauss weaponry and associated tech use ferrous materials in the projectiles/other thing used.

[Seret]

I never really said this was practical. I would just like to know, could this produce SOME power?

Of course. Move a conductor through a magnetic field you'll always get some. Likewise move a field through your conductor (eg: an alternating field that expands and collapses continuously) and you'll get power.