HAZARDS TO SPACE WORKERS FROM IONIZING RADIATION IN THE SPS ENVIRONMENT John T. Lyman Biology and Medicine Division - Lawrence Berkeley Laboratory Berkeley, California 94720 This report presents a compilation of background information and a preliminary assessment of the potential risks to workers from the ionizing radiation encountered in space. The report (1) summarizes the current knowledge of the space radiation environment to which space workers will be exposed; (2) reviews the biological effects of ionizing radiation considered of major importance to a SPS project; and (3) discusses the health implications of exposure of populations of space workers to the radiations likely to penetrate through the shielding provided by the SPS work stations and habitat shelters of the SPS Reference System. For the construction and maintenance of 60 SPS systems, each with a 30-year lifetime, it is estimated that about 50,000 man-years in space will be required. The hazards to the workers from the space ionizing radiation have been evaluated based upon the reference system scenario for a geosynchronous orbit (GEO) construction site. This will result in about 90-percent of the worker-years being spent in GEO. The number of maintenance workers needed per satellite is a large factor in the total space effort that is required. The three phases of the SPS mission, low earth orbit (LEO), the transfer ellipse (TE), and GEO will result in radiation exposure of space workers with different situations of time dependence, radiation quality, and ease of predictability. The various components of the radiation environment are described, and those important to each mission phase identified. LEO which is used for a staging area is fairly well shielded geomagnetically from the galactic cosmic rays (GCR) and the solar particle event (SPE) radiation. The major radiation hazard in LEO is from the trapped protons at the South Atlantic anomaly. During the transfer between LEO and GEO the workers must pass through the high radiation regions of the Van Allen belts. Depending on the trajectory chosen, either the bremsstrahlung radiation from the electrons or the protons can be the major contributor to the total dose equivalent. Lower dose equivalents are expected to be received in the trajectories that minimize the proton dose. In GEO the major contributor to the total dose equivalent will be the bremsstrahlung radiation from the electrons in the outer radiation belt. The GCR radiation is a fairly constant background of particle radiation that will be only slightly affected by the shielding of the reference system. Of the GCR, protons and helium ions are the largest contributors to the total flux, however, the HZE particles are more important in the calculations of the total dose equivalent. In addition, HZE particles may cause important biological effects not seen with low-LET radiations. Therefore the use of a quality factor to arrive at the dose-equivalent may result in underestimation of the health risks of exposure to HZE particles. Most of the dose equivalent will be received in GEO and in the transfers between LEO and GEO. SPE radiation is expected to significantly increase the
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