Free Astronomy Magazine September-October 2019

SEPTEMBER-OCTOBER 2019 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 GCR spectrum 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 ( α particles), 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 the