Are galactic cosmic rays the number one threat to manned spacecraft?

Galactic cosmic rays are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.

- Wikipedia, 2011

I am remembering something I read about the two types of space radiation common in our solar system, and how the intensity of this radiation is somewhat predictable using historical data and recent activity. My recall may be faulty, but the premise was something like the expected danger period actually coincided with plans for renewed manned space travel. Now there's the rub ...

Can any readers provide links to articles on this topic? I will do a much longer blogpost when I have some data regarding solar flares and space radiation and the risks to manned space travel. My theory involves promoting the use of robots during the dangerous radiation periods, and resuming human space travel only after the extreme danger fades away.

Any insight into which coming years and decades have the most risk will be greatly appreciated, please post links and info in Comments section below.


from Wikipedia, http://en.wikipedia.org/wiki/Galactic_cosmic_ray ; http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays