would be required for workers on the upper surface of the receiving antenna. Workers in supporting on-site facilities could be protected by architectural shielding. In GEO, transmitting equipment may have to be turned off during maintenance. Shielding provided to space workers against the GEO space environment would also serve as microwave protection for some tasks. The limit of protection that can be achieved could affect the choice of system parameters and could guide system design and operational strategies. There are no definitive data available to assess whether the microwave radiation associated with SPS operations might be harmful to ecosystems. Although information is available on the effects on specific animals or plant species in controlled laboratory environments, the data are insufficient for making an informed judgment on environmental effects on ecosystems in general. Honeybees have been studied thoroughly, and considerable data have also been obtained on birds since free-flying species could be exposed to the maximum power density at the receiving antenna site. The preliminary data obtained indicate that effects observed at peak SPS microwave exposure levels do not change behavior characteristics or affect survival. Extensive research is required to support a quantitative assessment of microwave effects on human health and ecosystems. International standards of microwave exposure will be required to guide the design of an SPS microwave transmission system, to estimate the environmental effects of the SPS system, and to ensure that the SPS will meet all applicable international standards for public and occupational exposures and compatibility with ecosystems. NONMICROWAVE HEALTH AND ECOLOGICAL EFFECTS The scope of SPS activities would greatly exceed the extent of other space activities considered to date. Construction of the SPS would require extracting material resources, shipping those resources to factories for processing and manufacturing, transporting finished products to a launch site, and launching the product to space for orbital assembly. Large areas of land would be needed for the construction of the SPS receiving antenna. Space transportation vehicles would have to be built and transported to the launch site, and factories and housing would have to be provided and various energy sources utilized during construction of the SPS and for the launch. Most of these activities would be conventional processes normally associated with mining, manufacturing, and transportation. Their environmental consequences -- and potential SPS-related impact -- can be assessed on the basis of experience with these related activities. Even if the SPS is not placed into operation, similar environmental impacts might occur because other energy conversion systems might be implemented to meet future demands. Terrestrial support activities and their effects on workers in terms of occupational illnesses and injuries would be governed by industrial safety measures at accepted levels. The principal risk will be to space workers during launch, space travel, and LEO and GEO operations. Growing rapidly is the scientific and engineering database for LEO operations regarding suitable protection for workers to live and work in space safely and to enjoy good health after returning to Earth. Many of the conditions required for the construction, assembly, and operation of the SPS in terms of medical safety and occupational criteria are already the subject of research. The medical effects include substantial acceleration and deceleration forces during launch and return to Earth, living and working in a weightless environment, and potential hazards of space radiation. The significant data accumulated for manned operations for extended periods under microgravity conditions in LEO can be acceptable for crews having a broad range of physiological characteristics. There is no substantial evidence that unpreventable or noncorrective adverse effects will be experienced by SPS space workers in LEO, and that if potentially adverse effects are identified in the future, ameliorating measures can be developed to avoid them. Of primary concern will be the exposure of space workers to ionizing radiations during transfer from LEO to GEO and during operations in GEO. The ionizing radiation environment is characterized by fluxes of electrons, protons, neutrons, and atomic nuclei. In LEO, electrons and protons are trapped by the Earth's magnetic field in the Van Allen belt. Unpredictable solar radiation resulting from solar events (solar storms) can endanger crews during the transfer from LEO to GEO. In GEO, trapped electrons, trapped protons, galactic cosmic rays, and solar events contribute to the radiation environment. Galactic cosmic rays originate outside the solar system and are made up of protons, atomic nuclei, electrons, and high-energy heavy ions (HZE). The biological effects of HZE are not well understood and could produce impacts of an entirely different character than other types of ionizing radiations. Solar events are not predictable and temporarily greatly increase the radiation in GEO. Preliminary calculations made for HZE and other types of ionizing radiation for SPS workers in GEO indicate that radiation exposure might exceed current limits recommended by National and International Commissions on Radiation Protection. The risk from ionizing radiations tn space could be reduced through carefully designed shielding of the space vehicles and the working and living modules through solar storm shelters. Concepts to limit such radiation exposure include a layered metal alloy shielding, bulk material shielding, and creation of magnetic or electric fields. Monitoring systems will be necessary to obtain comprehensive, immediate accounts of radiation conditions in places occupied by space workers. Personal dosimeters will also be required because of differences in exposures among individuals performing different tasks under varying conditions and work schedules.
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