Space Radiation Environment

Abstract

The space radiation environment is composed of energetic electrons, photons, and all naturally-occurring atomic elements, which are fully ionized. The particle types and energies vary with location in space and depend upon the level of solar activity and the strength of local magnetic fields, such as those found around some planetary bodies. Major sources of these particles are: (1) charged particles emitted by the Sun (solar cosmic radiation), such as electrons, protons, and other light nuclei, (2) charged particles, mainly electrons and protons, trapped by planetary magnetic fields, and (3) energetic electrons, protons and heavier ions, arriving from interstellar space (galactic cosmic radiation). For the latter, kinetic energies as large as 100 EeV (10²⁰ electron volts) have been observed. For crewed missions in low-Earth orbit (LEO), the main sources of crew radiation exposures are from Earth’s trapped radiation belts and galactic cosmic radiation. For missions beyond LEO, exposures to galactic cosmic radiation pose the greatest long-term risks, while radiations emitted in large solar energetic particle (SEP) events can result in near-term, acute health risks unless adequate shielding is available for crew protection.