Space radiation dosimetry in low-Earth orbit and beyond

Space radiation dosimetry presents one of the greatest challenges in the di scipline of radiation protection. This is a result of both the highly compl ex nature of the radiation fields encountered in low-Earth orbit (LEO) and interplanetary space and of the constraints imposed by spaceflight on instr ument design. This paper reviews the sources and composition of the space r adiation environment in LEO as well as beyond the Earth's magnetosphere. A review of much of the dosimetric data that have been gathered over the last four decades of human space flight is presented. The different factors aff ecting the radiation exposures of astronauts and cosmonauts aboard the Inte rnational Space Station (ISS) are emphasized, Measurements made aboard the Mir Orbital Station have highlighted the importance of both secondary parti cle production within the structure of spacecraft and the effect of shieldi ng on both crew dose and dose equivalent. Roughly half the dose on ISS is e xpected to come from trapped protons and half from galactic cosmic rays (GC Rs). The dearth of neutron measurements aboard LEO spacecraft and the diffi culty inherent in making such measurements have led to large uncertainties in estimates of the neutron contribution to total dose equivalent. Except f or a limited number of measurements made aboard the Apollo lunar missions. no crew dosimetry has been conducted beyond the Earth's magnetosphere. At t he present time we are forced to rely on model-based estimates of crew dose and dose equivalent when planning for interplanetary missions. such as a m ission to Mars. While space crews in LEO are unlikely to exceed the exposur e limits recommended by such groups as the NCRP, dose equivalents of the sa me order as the recommended limits are likely over the course of a human mi ssion to Mars. (C) 2001 Elsevier Science B.V, All rights reserved.