A STUDY OF THE RADIATION ENVIRONMENT ON BOARD THE SPACE-SHUTTLE FLIGHT STS-57

A joint NASA-Russian study of the radiation environment inside a SPACE HAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5 degrees inclination and 462 k m altitude. The locker carried a charged particle spectrometer, a tiss ue equivalent proportional counter (TEPC), and two area passive detect ors consisting of combined NASA plastic nuclear track detectors (PNTDs ) and thermoluminescent detectors (TLDs), and Russian nuclear emulsion s, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil techniqu e. The results show good agreement between the integral LET spectrum o f the combined galactic and trapped particles using the tissue equival ent proportional counter and track detectors between about 15 keV/mu m and 200 keV/mu m. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading . The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal proc essing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent cal culations. The results of the analysis of the spectrometer data will b e reported separately.