One potential issue that will be faced with long, manned, space exploration will be exposure to fluctuating radiation levels.
The current method of safety seems to be launching at times when radiation is low, avoiding solar flares, or hiding between the water tanks when it peaks unexpectedly.
This isn't really a sustainable, nor highly safe method of protecting from radiation.
What technologies or research is underway that will provide a higher level of safety to humans inside the craft on long exploration voyages?