Cosmic radiation (Cosmic radiation = Radioactive radiation) is a form of cosmic weather. And just like weather here on Earth, it is extremely variable. Radiation levels vary from day to day by as much as 100%. Existing tools based on monthly average readings are therefore imprecise measures of an individual's in-flight exposure to cosmic radiation - especially during solar storms.

When atomic particles collide with a human cell, several things can happen:

• The particles can pass straight through without causing any damage.
• The particles can damage the cell and cause it to die. A new cell will grow to replace the old, and no lasting damage is done.
• The atomic particles can also hit the strands of DNA located in the nucleus of the cell and cause DNA strands to break.

The human body is designed to cope with some exposure to cosmic radiation. DNA has a built-in ability to repair itself if damaged. But overexposure can cause the DNA to change - it can cause a mutation - and this mutation is potentially the beginning of a cancerous growth.