Space Radiation Dosimetry on U.S. and Soviet Manned Missions

Abstract

Radiation measurements obtained on board U.S. and Soviet spacecraft are presented and discussed. A considerable amount of data has now been collected and analyzed from measurements with a variety of detector types in low-Earth orbit. The objectives of these measurements have been to investigate the dose and LET spectra within the complex shielding of large spacecraft. The shielding modifies the external radiation (trapped protons, electrons, cosmic ray nuclei) which, in turn, is quite dependent on orbital parameters (altitude, inclination). For manned flights, these measurements provide a crew exposure record and a data base for future spacecraft design and flight planning. For the scientific community they provide useful information for planning and analyzing data from experiments with high sensitivity to radiation. In this paper, results of measurements by both passive and active detectors are described. High-LET spectra measurements were obtained by means of plastic nuclear track detectors (PNTDs) while thermoluminescent dosimeters (TLDs) measured the dose. A few flights carried active detectors—tissue equivalent ion chambers (TEICs), particle spectrometers (generally to measure the LET distribution), and particle rate counters. On some flights, thermal and epithermal neutrons were measured with the use of fission foils, and metal samples analyzed by gamma ray spectroscopy measured low levels of several activation lines. PNTDs consisting of different combinations of CR-39, polycarbonate, and cellulose-nitrate sheets have proved to be an effective means of measuring the high-LET spectra. To date, they have been used on all the Space Shuttle flights including Spacelabs 1 and 2, and the earlier missions of the Gemini, Apollo and Skylab series. The assembly of various types of detectors, especially the large numbers deployed in the crew compartments, modules, access tunnels, and pallets of Spacelabs 1 and 2, have provided the most comprehensive mapping yet available of the radiation environment of a large spacecraft in low Earth orbit. They demonstrate the efficiency and advantages of coordinated measurements with passive and active detectors. The dosimetric results accumulated for over twenty-five years indicate the difficulty of accurately predicting the total picture of radiation phenomena as it will be encountered by space station. crews and other future missions. Understanding the effects of different types and configurations of shielding is also of particular importance. Detailed results of the measurements and comparison with calculated values are described.