Research NMR magnets the size of several refrigerators already exceed 8-10T; they are superconducting and could after initial run up likely run for years with no power at all. They drift down over time but it likely not be a show stopper, and the cold of space would help them minimize cryogen maintenance times - it would be an activity on the way to or from the planet maybe? Edit: though the magnet itself wouldn't require continuous power, others added there would be pressure from the sun and say it could be counteracted by orbit geometry or active force being added.

So you thave ouched on an important limitation of electromagnets; they need to be cooled. In space, the vacuum surrounding this power hungry object would be inferior to air for heat transfer; heat merely seeps out slowly radiatively.

So there would be a major improvement in keeping heat low/improving system efficiency or to transfer heat away without cooking the crew after the turn the thing on.

Is that true? A superconductor magnet needs to be cooled down to temperature (say 4K), but does it generate heat once operating? Seems like heat would come from resistance in the coil, but this resistance is zero when at operating temperature.

It would consume power by fighting against incoming particles. This would end up as heat inside it.

A permanent magnet also fights against incoming particles, and doesn't seem to consume any energy. Why would an electromagnet be any different?

Edit: the permanent magnet will feel a force applied against it in the opposite direction, of course. In space, that's have to be countered by rockets though, not electrically in the current running through the superconductor, right?

> Why would an electromagnet be any different?

Because the incoming electrically charged particle induces current in the coils of the electromagnet.

A permanent magnet does not have to deal with that - even if there is current it doesn't affect the magnetism in a permanent way.

Think about an electric solenoid: A stationary electromagnet does not consume power, a moving one does as it acts on the external magnets.

Space is not cold, at least in the inner solar system. To say nothing of internal resistance, however small, sunlight would fall on it and warm it up.

Im not sure of your context; but yes an electromagnet is a non-starter here from the get go; dealing with all the mass and power issues, bad spacey thermodynamics.

Wouldn't you be able to use somewhat normal refrigeration, then put a thermoelectric cooler on the heat exchanger side? If you could get the TEC's high temperature side hot enough, would it radiate heat more efficiently? (I'm assuming that hotter items radiate more joules of energy than cooler)

How about using something like a Dyson-Harrop satellite https://en.wikipedia.org/wiki/Dyson–Harrop_satellite as the power source

Presumably PV panels. Although a really large RTG (nuclear thermal reactor) might work too. It really depends on the amount of power we're talking about.