V. C. 2. Space Environment Impact on Long-Term Manned Operations J. V. Bailey Medical Research & Operations Div. Earth orbital operations entail exposure of personnel to essentially continuous radiation fields ranging in intensity from almost negligible to very intense with the possibility of serious injury in a very short time. The actual radiation exposure rates to be experienced are dependent upon altitude and inclination of orbits, effectiveness of the space vehicle or suit for shielding the astronaut, and occurrence of natural events that modify the trapped radiation environment. The radiation protective guides (limits) adopted for spaceflight exposure are five or more times the current occupational radiation protection guides. The scientific basis for these space exposure limits is a large body of radiobiological data on radiation exposure of a variety of animal types extending over 50 years. However, the available human exposure data covers a time span of a little more than 20 years. In about half again as long, NASA will be flying significant numbers of people for up to a year at a time in a chronic radiation exposure situation that has no parallel in past applications of radiation technology. With the advice of the Radiobiological Advisory Panel, Space Science Board, National Academy of Sciences, NASA has established radiation protection guides (exposure limits) for the design of space programs such as the Space Station or the Solar Power Satellite Systems. Reference table V-C-8, these design limits were proposed with conditions as follows: "They are proposed on the assumptions that (a) they are to be used only for current space-mission and vehicle-design studies; (b) space missions of the next 10 to 20 years will will high-risk operations, and the radiation hazard should be considered realistically and in perspective with other inherent risks; (c) they will be subject to review and revision as additional pertinent information becomes available and before application to actual operations; (d) an active career in earth-orbital operations can be terminated at the end of any specific mission; (e) the number of people involved will be small and most will be in the older-than- 30 age group; (f) participants will be highly motivated volunteers well informed about the nature and extent of the radiation risk; and (g) the agencies concerned appreciate the desirability of keeping exposure as low as practicable by appropriate engineering and operational considerations." There is a complicating factor in the radiation environment at geosynchronous altitudes, the galactic cosmic rays. Referred to as HZE particles (for high atomic number, high energy), the galactic cosmic rays are
RkJQdWJsaXNoZXIy MTU5NjU0Mg==