[yongjik]

That "magnetic field to protect from radiation" part is pretty important, though. (ISS is inside the Earth's magnetic field.)

[readerrrr]

All you need is a couple of meters of water or earth. The base would be inside the comet at complete safety anyway, and detection can warn you to get inside in case of increased sun activity.

It is really easy if you have just a little material:

http://en.wikipedia.org/wiki/Radiation_protection#Shielding