Maintaining the iss's orbit using the interactions with the earth's magnetic field

[EpicRootHairCell]

Would it be possible to fit a powerful electromagnet to the iss in such away that it generates a force in the prograde direction large enough to counter the aerodynamic drag it experiences from the upper atmosphere? If it is possible it would greatly reduce the cost of maintaining the iss as propellant would not be needed to maintain the orbit.

[Javster]

One hurdle would be weight and power use

[Skyler4856]

Earths magnetic field, Its magnitude at the Earth's surface ranges from 25 to 65 microtesla, that's weaker than a bar magnetic, attempting to move a 500 ton object...

It simply isn't worth the cost

[peadar1987]

For very long conductors like those used in a momentum exchange tether this is actually a viable means of boosting and lowering the orbit. You use the spare generation capacity from the spin-up motors when they're not operational to pass a current through the tether.

[jwenting]

and another idea to create a perpetuum mobile machine hits the dust, inevitably.

[Lukaszenko]

Earths magnetic field, Its magnitude at the Earth's surface ranges from 25 to 65 microtesla, that's weaker than a bar magnetic, attempting to move a 500 ton object...

It simply isn't worth the cost

It's already moving. All you need to do is to balance out the air drag. My understanding, for example, is that ion engines are more than sufficient for this.

The fact that it's 500 tons is irrelevant. You've been playing too much KSP :-)

Edited June 3, 2014 by Lukaszenko

[Red Iron Crown]

and another idea to create a perpetuum mobile machine hits the dust, inevitably.

This is not a perpetual motion machine. The station would be interacting with the Earth, and would be supplying the power for the electromagnet.

[jfull]

and another idea to create a perpetuum mobile machine hits the dust, inevitably.

Er, no. This isn't the same as a perpetual motion/free energy/reactionless device.

it is 100 percent possible to derive a tiny amount of thrust by "pushing" against a planetary or solar magnetic field.

[softweir]

In theory it is possible to extend a long tether parallel to Earth's magnetic field and pump a current along it. You'd need charge-dumping systems at each end that use the surrounding plasma as a common-ground system, so one end of the tether is dumping electrons while the other is gaining them. This would all be powered by spare current from the solar panels.

In practice it is nowhere so easy. Experiments with orbital tethers have been unsuccessful, and a current-carrying tether might be very unstable due to interactions with the surrounding plasma - for instance, there would be a strong tendency for the plasma to create a fairly direct current in the reverse direction to the tether-current, with a consequent retrograde flow of plasma. Current-carrying plasmas in magnetic fields are inherently unstable (a prime difficulty in producing fusion), and perturbations in the plasma would interact with the tether causing all sorts of motions in every which direction. Also, you would ideally need a VERY long tether, with equal weights at the ends so as to provide the tension needed to keep it straight.

All these problems look like ones that could be solved with enough time and effort - and big, big piles of cash. With the future of the ISS in doubt, that cash isn't going to appear.

[BagelRabbit]

It is very possible to push against a magnetic field in this way and stably maintain an orbit. However, an electromagnet with a large enough charge to do so would require a rather large amount of power. If you're using that amount of power, it is far easier to just use it on powering an ion engine. Ion engines are very reliable, efficient enough to almost certainly outlive the satellite's electronics, and produce more force per unit of electricity than pushing against the Earth's magnetic field.

That being said, it's still a viable concept. I believe that it's been done before, at least in a laboratory, though I'm not sure.

[shynung]

In theory it is possible to extend a long tether parallel to Earth's magnetic field and pump a current along it. You'd need charge-dumping systems at each end that use the surrounding plasma as a common-ground system, so one end of the tether is dumping electrons while the other is gaining them. This would all be powered by spare current from the solar panels.

Like this?

[Skyler4856]

It's already moving. All you need to do is to balance out the air drag. My understanding, for example, is that ion engines are more than sufficient for this.

The fact that it's 500 tons is irrelevant. You've been playing too much KSP :-)

You seem to miss the point behind my argument, I was simply pointing out that you still need to provide a "counter-acceleration" to the station, and to develop, test, and launch a system capable of utilizing the magnetic field of the earth, seems like a horrific waste of resources, better just to use Ion engines, as you said

[softweir]

Like this?

*snip*

Exactly. I was considering a bi-directional current flow would be easier than trying to turn a km-long tether round, but the principle is the same.

[shynung]

...you still need to provide a "counter-acceleration" to the station, and to develop, test, and launch a system capable of utilizing the magnetic field of the earth...

Why provide something to counter the acceleration produced by the aforementioned system? Measuring its direct acceleration would yield the same results with much less hassle.

The boon on this magnetic-field-pusher device is that it is propellantless; it requires nothing aside from electricity (and being placed in a magnetic field) to produce thrust. Ion thrusters still need propellant to function, typically xenon gas, which have to be replenished every so often.

The only hurdles on using this technology are development costs and power requirements (which dictates effective system TWR, taking into account power generators and other subsystems). Otherwise, the concept is sound.

Edited June 3, 2014 by shynung

[christok]

The boon on this magnetic-field-pusher device is that it is propellantless; it requires nothing aside from electricity (and being placed in a magnetic field) to produce thrust. Ion thrusters still need propellant to function, typically xenon gas, which have to be replenished every so often.

Very true, but I wonder about the relative power and mass required for this compared to runing a vacuum pump + ion engine combination which would gather its propellant in-situ.

[SolarLiner]

Earth's magnetic field is largely used in space ... for rotation purposes. It's so easy to manipulate it to make an object turn. HST uses that, as RCS would quickly fill up the nearby space with gas dust, downgrading the photo quality. IIRC it is used in the ISS too to make it keep the same attitude.

But it cost lots of power, and is one of the worst methods to turn a ship if you have to constantly change attitude. So don't even think about powering something via these.

[Mazon Del]

Earth's magnetic field is largely used in space ... for rotation purposes. It's so easy to manipulate it to make an object turn. HST uses that, as RCS would quickly fill up the nearby space with gas dust, downgrading the photo quality. IIRC it is used in the ISS too to make it keep the same attitude.

But it cost lots of power, and is one of the worst methods to turn a ship if you have to constantly change attitude. So don't even think about powering something via these.

I assume HST = Hubble Space Telescope, and I am not certain this is correct. I am pretty sure the Hubble uses gyros to turn and aim itself. I know that is one of the problems it has every so often that required repairs. As far as the power costs, it should be 'easiliy' calculable how much power you need over a given length of tether to acheive the goal here. Besides, realistically the system likely wouldn't be 'on' constantly, it would just activate in bursts every so often (weeks?) to boost it back up. So you can shut down extraneous systems/experiments when you need to.

[Skyler4856]

Why provide something to counter the acceleration produced by the aforementioned system?

The deceleration is provided by drag, and I never questioned its possibility, only its feasibility.