There are several arenas of progress in radiation shielding. Magnetic shielding may be possible and development of new materials may be very possible with the explosion of nanotechnology advances. I just saw where a gallanium nickel allow was just patented that had 60 x the neutron absorbing capability of the previous material to hold nuclear radiative material. An "aerogel" for shielding is very possible I think. Remember, just the travel to and from planet mars requires requires at least a year in space. The development of a safe room to cut exposure by an order of magnitude so that 10 years is safe is I think very doable. I wouldn't expect full tours to last more than 2 years (initially) anyway. What do you think of the overall concept? Have you read about the concept anywhere else?