O
rion, NASA's
new manned
spacecraft. The
model below
shows its inte-
rior. Most of the
mass transported
is concentrated
on the bottom
and constitutes
an additional
shield against
possible peaks of
radiation from
the Sun. [NASA]we can do nothing. GCRs generally origi-
nate at a great distance from the Solar Sys-
tem during very violent phenomena, such
as stellar explosions. They are atomic nuclei
that move at relativistic speeds and possess
enough energy to penetrate any kind of
shield that can be made today. The GCRspectrum is a complex combination of ions
derived from most atomic species found in
the Periodic Table. Nearly 87 % of GCRs
consist of hydrogen ions (protons), 12 % of
helium ions (αparticles), and the remain-
ing 1 - 2 % of heavier nuclei, from lithium to
nickel and even, rarely, beyond.
It has been calcu-
lated that every cell
of an astronaut’s
body that travels
beyond low Earth
orbit is crossed by a
hydrogen ion every
few days. Every few
months, the astro-
naut himself is in-
stead hit by a
decidedly heavier
ion. Although infre-
quent, episodes of
the last type con-
tribute significantly
to the maximum
tolerable dose of
GCRs. The energies
of these heavy ions
make them so pen-
etrating that thespace radiation EN_l'Astrofilo 29/08/2019 15:44 Page 46