Page "Cosmic ray" Paragraph 5

Cosmic rays compose a part of natural background radiation on Earth, averaging about 10-15 % of it.

However, persons living at higher altitude can obtain several times more cosmic radiation than at sea level, and long distance airline crews can double their yearly ionizing radiation exposure due to this source.

Since the intensity of cosmic rays is much larger outside the Earth's atmosphere and magnetic field, it is expected to have a major impact on the design of spacecraft that can safely transport humans in interplanetary space.