[elihu]

I'm not very knowledgeable of radiation hazards in space, but from some casual wikipedia browsing, it appears that the primary hazard is from protons (and various charged particles) being spewed out from the sun.

How practical is it to use an electrically charged or magnetic object between the sun and the spacecraft to deflect particles? Presumably, the farther away it is the less deflection would be necessary, but at some point it would be too far away to effectively mask the whole disk of the sun.

Similarly, you could just use a physical screen. Apparently, things like aluminum don't work very well as shielding because the undesirable particles react with the aluminum and produce more undesirable particles. However, if it were far enough away from the ship, it wouldn't need to block the radiation, it would only need to deflect most of it in a slightly different direction. (Whether the "screen" is on a long tether or whether it's a separate drone-spaceship would be an implementation detail that's not particularly important.)

I assume there's some reason this is impractical, otherwise it would be a solved problem already...

(As for shielding on Mars itself, I'm okay with the idea that humans will spend most of their time underground.)