NASA uses aerogel to catch dust (was Mass is no longer a factor in r

> http://en.wikipedia .org/wiki/ Health_threat_ from_cosmic_ rays#Shielding
>
> "Electromagnetic shielding has a number of problems: (1) the fields
> act in opposite directions on positively and negatively charged
> particles, so shielding that excludes positively charged galactic
> cosmic rays will tend to attract negative ions; (2) a very large
> power supply would be required in order to run the electrostatic and
> magnetostatic generators, and superconducting materials might have to
> be used for magnetic coils; (3) the possible field patterns might
> tend to dump charged particles into one area of the spacecraft."
Back in the early days of space habitat research, they did look at a combination of magnetic and electric fields for radiation shielding before deciding that the idea was too cumbersome and not as reliable as mass shielding. An electric field by itself results in problem (1). A magnetic field by itself results in problem (3). So what they had advocated was charging the outer hull of the space habitat with a strong positive charge. This would repel the large, positively-charged nuclei (the most damaging kind of radiation). Left by itself, though, this would attract electrons, which would strike the hull and product X-rays. A magnetic field was then used to funnel the attracted electrons. This was smarter than doing it the other way around since the electrons were of much lower mass than even a single proton, and thus more easily deflected by a lower-power magnetic field. But as I said, in the end they decided that a passive mass shield was a moreelegant solution(and safer). Regards,
Mike Combs