Orbital power station concept

[NovaSilisko]

[Guest Flixxbeatz]

1.Will this even work?

That destroys the purpose, I guess...

[softweir]

It might work (if the orbital dynamics are right), but not for very long. As the tether section rotates around the main body it can be used to drive a generator. however, the generator will need to be anchored to the main body, so it will apply a torque to the main body, which will start to turn. Eventually the main body will be turning as fast as the tether section and the generator will produce zero power.

Photovoltaics and/or hydrogen/oxygen fuel cells and/or nuclear options are increasingly light, efficient and effective.

[TwoHedWlf]

And what is supposed to keep the generator equipment from rotating? Even ignoring whether the counterweights will spin...

[icefire]

I vaguely remember reading something about gravity gradient torque and its effect on symmetrical vehicles.

If I remember correctly this would just stabilize along the velocity vector, not rotate. Either that or it will just decay the orbit, take your pick.

[Iskierka]

Comments made in IRC, unedited.

2019-45 <NovaSilisko> not sure if valid idea

2019-46 <NovaSilisko> or just silly

2021-23 <Fircyk> there\'s nothing to inherently spin them

2022-41 <Fircyk> even if there was, there\'s nothing to cause the two to spin independently

2023-15 <Fircyk> and gravity gradient would most likely cause rotation you give it to decay to near-nil

2023-26 <NovaSilisko> that\'s what i was afraid of

2023-51 <Fircyk> could get power generation using a similar structure

2023-55 <Fircyk> but it would decay its own orbit

2024-08 <Fircyk> (said method being to use induction from the earth\'s magnetic field)

2024-17 <NovaSilisko> but wouldn\'t 200 km total separation between the two counterweights be enough to have a gravity gradiant?

2024-30 <Fircyk> any separation is enough for gravity gradient

2024-45 <Fircyk> but I think there are a few people who have gotten an idea that gravity gradient will accelerate the near side

2024-56 <Fircyk> counterpoint A) does the moon spin?

2025-20 <NovaSilisko> i was thinking because the tethers are on their own axis, separate from the main spacecraft weight

2026-33 <NovaSilisko> damn you physics!

2026-51 <Fircyk> they could momentarily spin a central mechanism, IF there was anything to spin them. But the main craft would catch up fairly rapidly, decent generators have decent rotational resistance

2027-39 <NovaSilisko> so large photovoltaics are still the best option of power generation from orbit

2027-49 <Fircyk> on a large scale, yes

2028-01 <Fircyk> like I said you can use induction to generate the power for a small satellite

2028-35 <NovaSilisko> yeah, i had heard of that

2028-45 <NovaSilisko> i was just wondering if it was possible to use orbital motion itself to rotate the craft

2029-04 <NovaSilisko> the central generator would be held in place with a gyroscope like lots of satellites use to keep their orientation

2029-20 <NovaSilisko> though would angular momentum alone be enough to keep it oriented?

2029-45 <Fircyk> it would gradually be overcome. again, if there was something to keep it going

2030-15 <Fircyk> free orbit at a lower altitude has a different orbital velocity, but unless you accelerate it, it will simply exert tension on the cable

2030-29 <Fircyk> in order to overcome the extra gravity

[LukeTim]

I\'m not sure I understand how this is supposed to work...

Is it a typical turbine generator and the counterweights make it turn during the orbit?

Do they make it turn because of the orbit? Wouldn\'t that mean the period would be 24 hours and the current would be effectively 0A? Can\'t be that...

IDGI.

[Iskierka]

The idea was meant to be that since orbit should be faster 200 km or so away (example figure for tether length), it should be forced to rotate and produce power.

Unfortunately gravity gradient works the other way.

[LukeTim]

The idea was meant to be that since orbit should be faster 200 km or so away (example figure for tether length), it should be forced to rotate and produce power.

Unfortunately gravity gradient works the other way.

If you set something spinning in space, presumably it will keep spinning due to lack of air resistance... so could you not just stick a magnet and a solenoid up in orbit and get the magnet spinning relative to the solenoid?

[softweir]

If you set something spinning in space, presumably it will keep spinning due to lack of air resistance... so could you not just stick a magnet and a solenoid up in orbit and get the magnet spinning relative to the solenoid?

It takes energy to get them spinning relative to each other, and inefficiency in the solenoid will mean you get less energy back than you put into it!

About the only non-photovoltaic 'free' orbital energy system I can see working would be one that somehow uses the dayside/nightside compression/expansion of the Earth\'s magnetic field to create eddy currents in, say, an orbital tether, but even that is more likely to end up converting orbital momentum into electricity and leaving one with a decaying orbit!

[Hypocee]

You will get back some fraction of the energy you put into blasting the thing into orbit.

[Iskierka]

If you set something spinning in space, presumably it will keep spinning due to lack of air resistance... so could you not just stick a magnet and a solenoid up in orbit and get the magnet spinning relative to the solenoid?

There is no aerodynamic resistance, but any generator has some impressive electrodynamic resistance.

Final word: There is no such thing as free energy. If you try take energy from an orbit, you\'ll just decay the orbit, at best. That\'s why the proposal is for photovoltaics; there may not be free energy, but the sun is certainly kicking plenty our way to be collected.

[mincespy]

How are you planning to achieve geostationary orbit when Kerbin dosen\'t spin?

[Iskierka]

This is off-topic. Doesn\'t have to be kerbin.

[sneakeypete]

Final word: There is no such thing as free energy.

ding ding ding, we have a winner!

on the topic of space based solar panels... i honestly can\'t see it being particularly feasible for a while yet. The cost of getting them into orbit and the cost+losses of beaming energy back means that ground based panels have a lot of advantage. Not to mention they\'re easier to service. And the whole microwave transmission fear that people will have.

[HarvesteR]

Provided this thing does work as advertised, I think you\'d spend more energy in countering the torque from the spinning counterweights than you\'d get back from the generator...

I\'m assuming, of course, that the counterweights are attached somehow to the central hub... Be it a very very efficient ball bearing or even a magnetic floater bearing, there will be a torque applied to the thing, and you\'ll have to compensate by spinning something in the opposite direction. I doubt this system would provide enough energy to even keep the central hub from joining in the rotation... much less to spare.

Cheers

[TwoHedWlf]

Provided this thing does work as advertised, I think you\'d spend more energy in countering the torque from the spinning counterweights than you\'d get back from the generator...

I\'m assuming, of course, that the counterweights are attached somehow to the central hub... Be it a very very efficient ball bearing or even a magnetic floater bearing, there will be a torque applied to the thing, and you\'ll have to compensate by spinning something in the opposite direction. I doubt this system would provide enough energy to even keep the central hub from joining in the rotation... much less to spare.

Cheers

And the spinning counterweights will eventually become tidally locked anyway. The kinetic energy lost being turned into heat in flexing of the bars between them.

[Arrowstar]

Gravity gradient torque will ultimately slow down the rotation you provide initially until the vehicle is effectively standing still w.r.t. the planet. Won\'t work.

[Hypocee]

Actually it\'ll still 'work'. It was so obvious that it\'d become tidally locked that I initially assumed that was the intent. You\'d then have the sidereally-fixed gyros rotating relative to the satellite once per orbit. Net result, you\'re using your satellite as a flywheel, slowly deorbiting it for a trickle of energy. Insane in the inner solar system, it could make sense for a planetary orbiter farther from the sun, though the need for heavy gyros and heavy counterweights makes me skeptical even of that.

[icefire]

when solar isn\'t an option nuclear is used

[Hypocee]

I know. But if you hadn\'t discovered nuclear, or didn\'t have fissile material, or were bound by treaties or regulations not to launch a nuclear reactor...

[Herra Tohtori]

Tethered satellites have been researched for many purposes, including power generation. Actually, the proposed designs are simpler than here.

Electrodynamic tether works by inducing an electron potential differential (also known as voltage) between the two ends of the tether as it travels through the planet\'s magnetic field.

Now, this alone would do nothing except make one end of tether positively charged and the other end negatively charged... However, there are charged particles bouncing around in the space, and you can collect and emit them. The positively charged end of tether would attract free electrons, while negatively charged would repel, and actually emit electrons, if I understood the idea right. This way, you can drive current through the system: Electron emitting end (cathode) works as ground, while the electron collecting, positively charged end, works as the +V input.

The induced current does create a force on the tether, which affects the momentum of the spacecraft; therefore there are limits to how much power you can generate this way. However, this also allows possibilities for orbital maneuvering, as if you drive a current through the tether, you can induce a force on the spacecraft to create a form of electromagnetic propulsion.

[DoctorEvo]

At first, I misunderstood your picture and thought you were suggesting harvesting Earth\'s rotational kinetic energy via tension in a space-elevator-esque tether (which, in theory, WOULD work, but would not be worth the expense from an engineering standpoint).

But now that I understand what it actually IS... No, of course it wouldn\'t work. :

Actually it\'ll still 'work'. It was so obvious that it\'d become tidally locked that I initially assumed that was the intent. You\'d then have the sidereally-fixed gyros rotating relative to the satellite once per orbit. Net result, you\'re using your satellite as a flywheel, slowly deorbiting it for a trickle of energy. Insane in the inner solar system, it could make sense for a planetary orbiter farther from the sun, though the need for heavy gyros and heavy counterweights makes me skeptical even of that.

Well, if it were possible to 'sidereally-fix' a gyro (which it isn\'t, all a gyro does is add angular momentum), I suppose that could work. But, as you mentioned, the energy yield would be pathetic unless you used absurdly large weights, and it would only be coming from the specific orbital energy of your satellite (which you had to pay for in the first place), so this idea is, needless to say, kinda pointless.