Why aren’t we better protected against galactic cosmic rays?

If exposure to cosmic rays is potentially harmful, why aren’t we better protected?  The answer is that galactic cosmic rays are very penetrating. It takes a very thick radiation shield to completely stop the type of cosmic rays that are encountered at high altitude.  Shielding the whole airplane would add too much weight to an aircraft.

Flying at a lower altitude is not an option. The fuel consumption of an airplane would be prohibitive at lower altitude.

Even measuring the dose is not easy. Traditional radiation badges are not sensitive to the type of particles found at high altitude. The best instrument to measure galactic cosmic rays is the size of a suitcase and requires hours of analysis to extract the dose.