I wouldn't say less. Eventually you get out into interstellar space and there things would be fairly constant. The effect there would be minimal. They would stay minimal until you approached a stellar system of some sort. It's Pioneer 10/11 and Viking 1 and 2 that would have some answers if the data's available.
Although some researchers have suggested that it would be better to go to Mars during a period of solar maximum when the sun is producing the most radiation, because then the sun has the strongest magnetic field which shields the solar system from very high energy galactic cosmic rays which would be impossible to shield against on your spaceship. |