A detailed study and understanding of the radiation environment in space and its effects on human physiology has a growing importance with current work on the International Space Station (ISS)
and of a future mission to Mars. Radiation in orbit comes from cosmic rays of different energies and origins.
In addition to the galactic component - which is modulated by the solar activity at low energies - there are also solar
energetic particles associated to transient phenomena such as Solar Flares or Coronal Mass Ejections.
Inside Earth's magnetosphere there is also the significant contribution of trapped particles: to the well-known proton and electron belts,
recent studies have shown a more complex nuclear composition, for instance, with trapped components of anomalous cosmic rays.
Cosmic ray environment in space
For Low Earth Orbits (LEO) such as those of MIR, ISS or Shuttle (altitude of 300-400 km, inclination of 51.6°) the effect of trapped radiation is mostly
evident in the South Atlantic Anomaly (SAA). This is a region located between South America and Africa were the orbit of LEO spacecraft crosses the inner radiation.
It is also important to study the cosmic ray nuclear component for its high quality factor which - even with a low flux -
can give a non-negligible contribution to the dose absorbed by astronauts.
Cosmic rays provide a unique probe of the most energetic processes in the Universe.
Cosmic rays are electrons, positrons, protons, antiprotons and atomic nuclei, light as deuterons and alpha,
produced in the primordial nucleosyntesis, or heavier, coming from the explosion of supernova stars, from which all
surrounding electrons have been stripped away during their high speed passage through the galaxies. Cosmic rays come mostly
from outside the solar system but generally from within our galaxy (Galactic Cosmic Rays). They have been accelerated to nearly the speed of light,
within the last ten million years, and have travelled many times across the galaxy, trapped by the galactic magnetic field.
While astronomical observations of light from distant objects yield clues to the state of matter in our galaxy and beyond, cosmic rays bring us a small but
valuable sample of that matter itself. Through studies of the composition and energy spectra of cosmic rays, we are able to learn about the origin and
evolution of material in our galaxy and about fundamental physical processes that govern its dynamics.
In addition to the interest related to fundamental physics, cosmic rays are the source of radiation absorbed by astronauts and therefore involve many health physics and medical issues.
These not only include the measurement of the radiation dose but also other effects such as the Light Flash phenomenon. Even though the doses absorbed are below safety margins in solar quiet conditions, they could increase to high values in case of a big solar particle event, especially during a mission outside the Earth's magnetosphere.
Up to now only Apollo missions have carried man outside the protective shielding of the geomagnetic field and only for a relatively short time (10 days).
In case of a longer (3 years) mission to Mars, the crew would be exposed not only to the small (but continuous) component of Galactic cosmic Rays but to the sporadic but potentially very intense component of Solar Cosmic rays generated by solar flares and Corona Mass Ejections.
Even for shorter and "safer" missions in Low Earth Orbit a continuous monitoring of the dose absorbed by the astronauts and its relation with their health is necessary
for a complete assessment of the risks and the effects encountered during space flight.
In addition to passive and active dosimetric measurements it is also required a detailed study of the different nuclear component of cosmic rays.
Cosmic rays in the magnetosphere are deflected from the geomagnetic field according to their energy,
charge and angle of incidence. The shielding is higher at the magnetic equator and lower at the poles: this means that at the equator only higher energy particles can reach and penetrate the spacecraft,
resulting in a higher flux and dose at the poles. A notable exception to this rule of thumb is the South Atlantic Anomaly (SAA), where the magnetic field is lower (due to multipole terms)
and thus particle flux is higher. Particles in the SAA are mostly protons trapped in the inner Van Allen Belts: therefore flux can increase up to three orders of magnitude in this region.