Could superconducting magnets be used to form a shield around a spacecraft? If superconducting magnets could be used in space to form a field around a spacecraft of a similar field strength on the earth 25 to 65 microtesla's?


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*Would the temperature in space at -246c be OK for superconducting magnets to work with no energy penalty?

*Could the cryogenic fuel be used to help cool the superconducting magnets?
 A: These schemes have been proposed and studied. A spacecraft with a magnetic field could steer charged particles away from it.
The magnetic field would have to be much stronger than the Earth's magnetic field. The reason is pretty easy to see. The Lorentz for $\vec F~=~q\vec v\times\vec B$ for the charged particle velocity perpendicular to the magnetic field gives circular motion
$$
m\frac{v^2}{r}~=~qvB
$$
and this gives the cyclotron radius of the charged particle 
$$
r~=~\frac{mv}{qB}.
$$
This equation holds for a constant magnetic field over the radius of this motion. For charged particles deflected by the Earth's magnetic field this condition approximately holds over thousand of kilometers. The Earth' magnetic field $B~\simeq~.5$Gauss is large and extensive in space. We are not able to do this.
For spacecraft applications you would need to deflect charged particles over a radius of about $10$ to $100$ meters. By just using ratios with the cyclotron radius above it is easy to see you would need a magnetic field on the order of $10^4$ to $10^5$ Gauss or $1~-~10$T. This is one or two order of magnitude smaller than the largest magnetic fields generated on Earth. So it would not be an easy technical feat.
A: The temperature in space is not as easy thing, because it is not clear, what is actually whose temperature we want to know. On the Earth, the temperature in the meteorology means the temperature of the air in shadow. But there is no air in the space. The cosmical microwave background has a temperature of around 2.7K, but it is -270C and not -246C.
But in the Solar System, or nearing a star, there are also the photons of the nearby star. Their energy distribution is not thermal, but we can assign a temperature to them by saying with which temperature they have a thermal equilibrium. On the orbit of the Earth, it is around +10C (not surprising - the Earth radiates exactly the same power, as it gets from the Sun. Or else it would be overheated or cooled down).
Short answer: Magnetic field shields only against charged particles, for example it would be practically negligable against laser weapons or against an electrically neutral space torpedo.
Yes, there are superconductors on -246C, but they are incapable to construct a really strong magnetic field. Industrial superconductors are cooled by liquid Helium until now.
