PRELIMINARY EXAMINATION OF SATELLITE POWER SYSTEM (SPS) OCCUPATIONAL HEALTH IMPACTS October 2, 1978 JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFORNIA
900-820, Rev. A PRELIMINARY EXAMINATION OF SATELLITE POWER SYSTEM (SPS) OCCUPATIONAL HEALTH IMPACTS October 2, 1978 Peter Tin-Yau Poon Lawrence R. Baker Ta-Jin Kuo Marshall E. Alper, Manager Solar Energy Program JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFORNIA
900-820, Rev. A DISTRIBUTION NASA HEADQUARTERS H. Calahan (2) --------------------------------Code NT D. Cauffman-----------------------------------Code ST J. Disher-------------------------------------Code MT S. Fordyce------------------------------------Code ECF H. Fosque-------------------------------------Code TA T. Hagler-------------------------------------Code MTE R. Johnson------------------------------------Code MTE R. LaRock-------------------------------------Code NT S. Manson (5) -------------------------------- Code NT S. Sadin------ Code RX E. Schmerling---------------------------------Code ST S. Tilford------------------------------------Code SU D. Winter (2) -------------------------------- Code SB Department of Energy Solar and Geothermal F. Koomanoff (5) Code DSE Battelle-PNL J. Madewell Code DSE Box 999 H. Marvin Code DSE Richland, WA 99352 E. Willis Code AIR Attn: W. Bair (5) Department of Energy Environment R. Blaunstein (6) Code DTO M. Minthorn, Jr. Code DBER Argonne National Laboratory 9700 South Cass Avenue Argonne, IL 60439 Attn: T. Wolsko (6) Argonne National Laboratory 400 N. Capitol Street NW Washington, DC 20001 Attn: C. Sandahi Los Alamos Scientific Laboratory Box 1663 Los Alamos, NM 87545 Attn: J. Hopkins (3) Planning Research Corporation 7600 Old Springhouse Road McLean, VA 22101 Attn: C. Bain (4) Solar Energy Research Institute 1536 Cole Boulevard Golden, CO 80401 Attn: P. Rappaport JOHNSON SPACE CENTER G. Arndt --------------------------------------Code EJ5 L. Bell (3) -----------------------------------Code EZ C. Covington (4) ------------------------------- Code EW4 H. Davis--------------------------------------Code ER 0. Garriott (1) -------------------------------Code CB J. Loftus -------------------------------------Code A R. Piland (7) --------------------------------- Code EA4
MARSHALL SPACE FLIGHT CENTER K. Fikes (15) ---------------------------------Code PD11 C. Guttman (5) --------------------------------Code PS04 J. Murphy-------------------------------------Code PA01 G. von Tiesenhausen-------------------------- Code PS01 LEWIS RESEARCH CENTER J. Ward (2) ----------------------------------Code 49-3 AMES RESEARCH CENTER B. Newsom------------------------------------- Code 239-8 Dr. J. Sharp---------------------------------- Code 200-7 P. Sebesta------------------------------------ Code 236-5 JPL INTERNAL DISTRIBUTION M. Alper 506-406 J. Bowyer 507-228 H. Cotrill, Jr. 198-112D K. Dawson 198-102 R. Dickinson 238-528 D. Dipprey 198-102 R. Forney 506-418A E. Framan 506-410 R. Goldstein 122-123 T. Kuo 506-328 M. Lavin 506-436 F. Livingston 506-328 R. O’Toole 506-302 D. Ross 198-220 J. Spiegel 506-328 I. Stein 198-220 R. Stephenson 506-318 V. Truscello 5O2-2O1B P. Wiener 198-220 EXTERNAL DISTRIBUTION Aerospace Corporation Los Angeles, CA Attn: M. Wolfe Arthur D. Little, Inc. Cambridge, MA Attn: P. Glaser Boeing Aerospace Seattle, WA Attn: G. Woodcock (2) Convair San Diego, CA Attn: E. Bock ECON Princeton, NJ Attn: G. Hazelrigg Grumman Aircraft Corporation Bethpage, NY Attn: J. Mackovciak, Jr. (2) Raytheon Corporation Sudbury, MA Attn: 0. Maynard Rockwell International Space Division Seal Beach, CA Attn: G. Hanley (2)
ACKNOWLEDGMENT The authors wish to acknowledge the support of Floyd Livingston for his contribution and encouragement. They also acknowledge the support of Edward Koprowski in the area of space radiation and its hazards.
FOREWORD The Jet Propulsion Laboratory (JPL) has conducted a preliminary study on the potential impacts and benefits of Satellite Power Systems (SPS) that may be used to partially fulfill the Nation’s energy need in the 21st Century. In this report the results of a preliminary examination of occupational health impacts associated with the SPS are presented. This work was carried out under NASA RTOP 776-10-02 dated March 1, 1976 (subsequently redesignated RTOP 775-13-16), under the technical management of Mr. Simon Manson of the Solar Energy Division of the NASA Office of Energy Programs.
ABSTRACT This report deals with impacts and benefits to occupational health associated with the Satellite Power System (SPS). This includes injuries and illnesses which occur in all phases of the SPS, from the acquisition of the raw materials to the final operation and maintenance of the Satellite Power System. In each phase of the SPS, the manpower is broken down into categories of each type of job and into a listing of the Occupational Health Impacts in terms of person-days lost due to occupational injuries and illnesses, from which the main areas of impact can be found. It is indicated in this report that 99.86% of the manpower required for SPS would be engaged in conventional occupations. For this manpower, the incidence of occupational health impacts is computed to be 7% higher than the national average of all ground-based industries. For the 0.14% of SPS manpower engaged in space operations that are unique to the SPS, there is no data base for assessment of occupational health impacts. In this area, the hazards are discussed qualitatively. Recommendations for further studies are presented in the report.
CONTENTS PAGE Notice .......................................... 1 Summary .......................................... 1 I. Description of SPS System Scenario A.............. 1-1 II. Methodology...................................... 2-1 III. Occupational Injuries and Illnesses ............... 3-1 IV. Space Assembly, Fabrication, Construction, Operation and Maintenance .................... 4-1 V. Space Radiation Hazards in LEO and GEO............. 5-1 VI. Recommendations.................................. 6-1 References........................................ R-l
CONTENTS (Cont) Table Page 1. Program Model Summary for Truss-Supported Photovoltaic 10-GW SPS Stations Built in LEO......1-2 2. Program Model Summary for Truss-Supported Photovoltaic 10-GW SPS Stations Built in LEO........ 1-3 3. Incidence Rates for Conventional Occupations for 100 Man-Years.............................. 2-4 4. Normalized Occupational Health Impacts for One 5-GW Rectenna Site........................ 3-1 5. Normalized Occupational Health Impacts for One Launch Site................................ 3-2 6. Normalized Occupational Health Impacts for One Space Transportation System Unit ........ 3-3 7. Normalized Occupational Health Impacts on the Ground for Components of One 10-GW SPS Station . . . 3-4 8. Normalized Occupational Health Impacts on the Ground for the Total SPS Scenario A............ 3-5 9. Radiation Exposure Limits and Exposure Rate Constraints for Unit Reference Risk............ 5-8 Figure Page 1. Matching Manpower and Incidence Rates................ 2-3 2. Orbital Integration Map - Solar Maximum Protons . • • 5-2 3. Orbital Integration Map - Solar Minimum Protons . . • 5-3 4. Radiation Attenuation 500 km - Solar Minimum Period. 5-5 5. Radiation Attenuation 500 km - Solar Maximum Period . 5-6 6. Radiation Attenuation - Geosynchronous Orbit .... 5-7
NOTICE This report is a record of studies sponsored by the National Aeronautics and Space Administration during 1976 and early 1977. The results and recommendations reported herein do not necessarily represent the official position of the U.S. Department of Energy concerning the potential occupational health impacts of the Satellite Power System (SPS) concept. SUMMARY Occupational health impacts have been assessed for 99.86% of the total manpower for the Satellite Power System (SPS) Scenario A in terms of person-days lost (PDL) due to occupational illnesses and injuries (see description of Scenario A, page 1-1). This percentage represents those SPS workers who are engaged in conventional ground occupations which are not unique to the SPS system; e.g., concrete work and trades. The results by subsystems are summarized below. The normalizing factor is 1.325 x 107 MW-yr, which is the number of MW-years produced in Scenario A when the SPS stations and the rectennas operate at a load factor of 0.92: Note that the space transportation systems and the rectennas account for more than three-quarters of the PDLs. An alternative summary of the PDLs by occupations is as follows:
This tabulation shows that the material acquisition phase has the highest occupational health impacts (slightly more than half the total PDLs), followed by construction, operations and maintenance. The incidence rate of occupational health impacts computed with the foregoing results is 57 PDL/100 Man-yr; this is 7% higher than the national average for all ground-based industries (53.3 PDL/100 Man- yr) . It should be noted that any jobs that will be unique to the SPS system, such as space fabrication, construction, operation, and maintenance, do not now have any statistics or history available on occupational health impacts. These jobs amount to 0.14% of the total manpower. Consequently, in relation to these tasks, this study only points out the various types of occupational health hazards and impacts that may exist. These occupational health hazards, which are discussed in Section V, are as follows: (1) Absence of life supporting elements in the space environment (2) Space radiation hazards (3) Microwave hazards (4) Solar UV hazards (5) Space charge (6) Meteoroids
(7) Collisions (8) Explosions and/or fires (9) Psychological effects (10) Contamination (11) Pressure excursions (12) Motion sickness A preliminary study of the space radiation environment and parametric depth dose relationship has been made for both solar maximum and solar minimum activities. The analysis covers geomagnetically trapped protons and electrons, electron-Bremsstrahlung radiation, and solar and galactic cosmic protons. The study shows that for LEO the most damaging radiation affecting the occupational health is trapped protons; whereas for GEO the solar flare proton dose predominates. The study shows that for the same allowable dose limit the shielding thickness required for GEO is about an order of magnitude higher than that required for LEO. Radiation in a space vehicle can be reduced below the levels computed in the study by using a sandwich method fusing different metals, e.g., aluminum and lead. A great deal more research and development into the makeup of the walls of the various spacecraft will be necessary. This research will be needed to determine the dose to a space worker on his long-term stay in space. Also, a designed ’’storm cellar” will be needed for any time there is a solar flare. A ’’storm cellar” would have extremely thick walls to give the personnel the protection needed.
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SECTION I DESCRIPTION OF SPS SYSTEM SCENARIO A To assess the occupational health impacts associated with -SPS. the implementation Scenario A developed by NASA JSC in Reference 1 will be used. This system would provide 25% of the new electrical energy demand by A.D. 2015. The Scenario A program model summary of a truss SPS constructed in Low-Earth Orbit (LEO) is illustrated in Tables 1 and 2 for A.D. 2000 through A.D. 2025. Only the initial 48 10-GW SPS stations are considered in the use of resources; however, it is expected that additional stations will be implemented beyond A.D. 2025 as required. The Scenario A follows the initial 48 SPS stations through the construction, operations, and maintenance phases. Only one SPS station is built during the first2years, then SPS stations are built at one per year for 8 years, two stations per year for the following 6 years, and finally three stations per year for 9 years between A.D. 2016 and A.D. 2024. With a projected lifetime of 30 years, the first SPS station must be replaced or refurbished in A.D. 2032 and the others in sequence after this year in order to maintain the electrical power generation of 480 GW. (See Tables 1 and 2.)
Table 1. Program Model Summary for Truss-Supported Photovoltaic 10-GW SPS Stations Built in LEO (Scenario A of Reference 1)
Table 2. Program Model Summary for Truss-Supported Photovoltaic 10-GW SPS Stations Built in LEO (Scenario A of Reference 1)
SECTION II METHODOLOGY The occupational health impacts associated with material acquisition, fabrication, construction, operations and maintenance of the SPS system are investigated according to the following methods. A. CONVENTIONAL OCCUPATIONS For those types of work which are not unique to the SPS, such as concrete work required for the construction of the rectenna systems, a quantitative approach to the occupational health impacts is adopted. The occupational injuries and illnesses can perhaps be estimated from the manpower requirements for the SPS (Livingston, et al, Ref. 2) and from the statistics provided by the Bureau of Labor Statistics, U. S. Department of Labor (Ref. 3). This method is applied to determine the occupational health impacts for material acquisition, fabrication, and construction of the rectenna systems, the launch sites, space transportation systems including propellants, and ground fabricated parts for the SPS stations. The occupational impacts are described in terms of the following parameters: (1) Person-days lost (PDL) due to occupational injuries (2) Person-days lost (PDL) due to occupational illnesses The number of fatalities is an additional valid parameter; however, it is not considered in the present assessment since the State and Federal publications do not have the incidence rates for fatalities. The conventional types of occupations can be classified according to the following industries: metal mining, sand and gravel mining, chemicals and allied products, primary metals industries, fabricated metal products, concrete, gvpsum and plaster, space vehicles construction, contract constructions, ground operations and personnel, and operations and maintenance. The relevant occupational health statistical inputs are the incidence rates. These incidence rates for a given calendar year, as defined by the U.S. Bureau of Labor Statistics,
represents the number of injuries or illnesses or lost workdays per 100 full-time employees in that calendar year: Total number of recordable injuries and/or illnesses or lost workdays Incidence rate = ---------------------------------- x 200,000 (1) Total man-hours worked by all employees in a given calendar year The numerical factor 200,000 is the base for 100 full-time equivalent workers, working 40 hours per week, 50 weeks per year. The manpower estimates and the incidence rates are matched to give the PDL for occupational injuries and illnesses, respectively (see Fig. 1). Equation (1) can be used to estimate the person-days lost in each of the conventional occupations. Denoting by (PDL)^ the total number of person-days lost in the i^ occupation and re-arranging equation (1) to solve for this term. th In equation (2) the incidence rate for the i occupation is obtained from data compiled by the Bureau of Labor Statistics, shown in Table 3. t h The total manhours worked in a year by SPS employees in the i occupation is obtained from the SPS manpower requirements estimated by F. Livingston et al (Ref. 2). The foregoing method applies to 99.86% of the total estimated manpower for SPS, whose work can be classified as belonging to the conventional occupations. B. OCCUPATIONS UNIQUE TO SPS For those workers engaged in production, operation and maintenance activities which are unique to the SPS system, such as space fabrication and construction in LEO and GEO or for operating and maintaining the
Figure 1. Matching Manpower and Incidence Rates
Table 3. Incidence Rates for Conventional Occupations per 100 Man-Years (Ref. 3) SPSs in GEO, the statistics on the occupational injuries and illnesses are not available since all occupational health data are based on past industrial surveys. Such space activity statistics will not be available for a long time, until sufficient experience of working in space is gained to be of statistical significance. Our method is to point
out the various types of occupational health hazards and discuss their associated impacts, instead of estimating PDLs for occupational injuries and illnesses. The types of work unique to the SPS are space fabrication and construction in LEO and GEO. and space operations and maintenance in both LEO and GEO. The total estimated manpower for such unique occupations amounts to 62.5 thousand man-years, while the total estimated manpower for the overall SPS Scenario A is 44.579 million man-years. Thus only 0.14% of the total SPS system manpower encounters unusual health hazards because of the unique working environment. The potential hazards are described in more detail in Section V.
OCCUPATIONAL INJURIES AND ILLNESSES The occupational health impacts associated with the material acquisition (including mining), fabrication, and construction have been estimated for the following systems (Refs. 2 and 3): (1) One 5-GW Rectenna Site (2) One Launch Site (3) One Space Transportation System (4) One 10-GW SPS (Material acquisition and ground fabrication) (5) Total SPS System Scenario A A. RECTENNA SITE The construction phase for a rectenna has the highest occupational health hazards (see Table 4) primarily due to the highest manpower Table 4. Normalized Occupational Health Impacts For One 5-GW Rectenna Site
requirement, followed by the fabricated metal products and primary metals industries. The normalizing factor for Table 4 is 480,000 MW __ n m _ _Q 5 MTT ----------- x 30 yr x 0.92 = 1.38 x 10 MW-yr. 96 rectennas B. LAUNCH SITE The construction industry again dominates the total occupational health impacts for the launch site (see Table 5) followed by the fabricated metal products and the primary metals industries. The operations and maintenance personnel for the launch site are included in the space transportation system to be discussed later. Since there are 21 launch sites for SPS Scenario A, Table 5 is normalized by Table 5. Normalized Occupational Health Impacts For One Launch Site Metal mining Sand and gravel mining Primary metals industries Fabricated metal products Concrete, gypsum, plaster Subtotal for material acquisition and fabrication Construction industry Operations & maintenance* TOTAL occupational health impacts
C. SPACE TRANSPORTATION SYSTEM UNIT A space transportation system unit is defined as all the HLLVs (Heavy Lift Launch Vehicles), PLVs (Personnel Launch Vehicles), COTVs (Cargo Orbital Transfer Vehicles), and POTVs (Personnel Orbital Transfer Vehicles), and other supporting facilities (except launch sites), which are associated with placing one 10-GW SPS from ground to GEO. Space vehicles manufacturing, fabrication of metal products, and the primary metals industries have comparable occupational health impacts. The PDL of these three categories of industries combined amount to about three- quarters of the PDL for the space transportation system (see Table 6). With 48 space transportation system units, the normalizing factor for Table 6 is 2.76 x 10$ MW-yr. Table 6. Normalized Occupational Health Impacts For One Space Transportation System Unit
D. SPS STATION The fabrication of metal products and the primary metals industries for the material acquisition and ground fabrication account for nearly all of the occupational health impacts for a 10-GW SPS (see Table 7). The normalizing factor for Table 7 is 2.76 x 10J MW-yr. Table 7. Normalized Occupational Health Impacts On the Ground For Components of One 10-GW SPS Station E. TOTAL SPS SYSTEM SCENARIO A The material acquisition and fabrication, construction, ground operation and maintenance of the 48 space transportation units have the most occupational health impacts in terms of PDL injuries and illness, followed closely by those of the 96 rectennas (see Table 8). The PDLs associated with all the occupational activities of the 21 launch sites and 48 SPS stations constitute less than one-quarter of the PDLs associated with the total SPS, except for those workers engaged in space assembly, fabrication, construction, operations and maintenance. All
entires in Table 8 are normalized by 1.325 x 10^ MW-yr, which is the total number of MW-yr produced in Scenario A when the SPS stations and the rectennas operate at a load factor of 0.92. Table 8. Normalized Occupational Health Impacts on the Ground for the Total SPS Scenario A
Table 8 may be re-arranged as follows: This tabulation shows that the material acquisition phase has the highest occupational health impacts (slightly more than half the total PDLs), followed by construction, operations and maintenance. The total PDL/MW-yr for SPS ground activities is obtained bv summing the values for occupational injuries and illnesses. Thus The United States national average incidence rate for all industries is 53.3 PDL/100 manyears. Thus, the computed overall SPS incidence rate is 7% higher than the national average. This may be understood by consideration of Table 3, which underlies the computed result. Table 3 indicates that the occupations which involve the highest incidence rates of occupational iniuries and illnesses are: concrete work, primary metals industries, contract constructions, and fabricated metal products. A large part of the total SPS manpower Then the SPS ground incidence rate is equal to The SPS overall PDL incidence rate can be computed from the relation,
belongs to these categories, hence the result computed for SPS is consistent with Table 3. F. OTHER OCCUPATIONAL HEALTH IMPACTS ON GROUND Other occupational health hazards which will have impacts on SPS personnel working on the ground are: (1) Microwave hazards at the rectenna site (2) Hazards associated with launch and boost The first hazard is being addressed in a companion study at JPL (Ref. 4) and the second type of hazard should be investigated in future impact and benefit studies.
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SECTION IV SPACE ASSEMBLY, FABRICATION. CONSTRUCTION, OPERATION AND MAINTENANCE In SPS Scenario A, the workers in LEO mainly consist of space assembly, fabrication, and construction workers (a total of 740 for every SPS station constructed) with very few operations and maintenance personnel (one worker for every two SPS stations constructed). After 25 years, when the assembly, fabrication and construction have been finished, there will be no more people working in LEO. In GEO, as in LEO, the production personnel (200 workers for each SPS station) dominate the number of operations and maintenance workers in GEO (12 per SPS station). However, after 25 years, when all the SPS stations have been set up, then there will be only the operations and maintenance personnel working in GEO for another 30 years. The employment of relatively small manpower involved in space assembly, fabrication, construction, operation and maintenance is made possible by the expected dominant role played by automation. For health and safety as well as economic reasons, automated machinery will be used as much as possible. Fewer people working in space translates into providing less supporting facilities in space and less time and expenditures for the intensive training required of the space workers. The occupational environment, assuming all proper measures have been taken, is still not as certain as on Earth. Furthermore, in case of the occurrence of a hazardous situation, it is much more difficult and expensive to rescue the workers than if they work on the ground. There are a number of occupational health hazards associated with working in LEO and GEO: (a) Absence of life supportive environment. The space environment is extremely lacking in the basic essential life supporting requirement, like air and water. (b) Space radiation hazards. Trapped electrons, trapped protons, protons from solar flares, and electron- Bremsstrahlung all constitute significant occupational health hazards. The space radiation environment, shielding
and dose limits will be discussed further in the next section (Section V). (c) Microwave hazards. A separate study on microwave hazards has been done in parallel with the present effort (Ref. 4). (d) Solar UV hazards. The short wavelength portion of the electromagnetic spectrum (40 to 4000 angstroms) may present an additional health hazard; however, astronauts will be reasonably well shielded in space suits during External Vehicular Activity (EVA) to minimize the hazard, and inside the space vehicle or space station UV is not a problem. (e) Space charge. There will be large voltage differences of the order of 20 kV between the SPS and the magnetosphere at certain times of the day. (f) Meteroids. Different sizes of material traveling in space coming from comets or the asteroids at various speeds (9 krn/sec to 20 km/sec) may hit a spacecraft. In the Apollo program, there were emergency plugs devised to plug any small holes that might occur as a result of collision with meteoroids. However, plugs may not be effective for larger holes; if a meteoroid about 6 inches in diameter were to strike and penetrate the wall of a space chamber, total decompression could occur rapidly. (g) Collisions. Possible collisions may occur, such as an SPS with another SPS, SPS with weather satellites, space debris, collisions with space tugs. (h) System or subystem malfunction. This may be caused by breakdown of components due to mechanical failures, faulty circuits, etc., resulting in lack of control or other modes of failure. (i) Explosions and/or fires. These may result from hazards (f), (g) , (h), or from other factors like improper storage of propellants.
(j) Psychological effects. Working in space has its associated psychological health oroblems that should not be ignored. They may be caused by factors such as personnel isolation as a group, limited recreational activities, and the constant awareness of hazards connected with the unique working environment. (k) Contamination. The working environment in a space vehicle is a closed one, and hence the problem of contamination is much more severe than on Earth. (1) Pressure excursions. Sudden changes of pressure may be experienced when transferring from one space vehicle to another if either cabin is not suitably pressurized. (m) Motion sickness. There may be sickness associated with weightlessness and bodily imbalance.
SECTION V SPACE RADIATION HAZARDS IN LEO AND GEO A. SPACE RADIATION ENVIRONMENT Space radiation hazards to personnel during SPS assembly, construction, operation, and maintenance in LEO and GEO include the protons and electrons of the trapped radiation belts, the solar flare radiation, and galactic cosmic rays. These radiations constitute the major biological hazards to crew members. A quantitative description of the radiation environment has been obtained from the published data through December 1976 of the National Space Science Data Center of NASA Goddard Space Flight Center (Ref. 5 and 6). Some typical maps for trapped protons for solar maximum and solar minimum are given in Figures 2 and 3 where the environmental data are expressed in protons/cm -day for various energies (in MeV) and for different altitudes (in nautical miles) for a given orbit inclination. To protect the space workers, shielding is needed to attenuate the trapped charged particles, and the corresponding derived radiobiological dose, to acceptable levels to meet mission dose criteria. This is a significant factor in the sizing of space compartments and other space vehicles proposed to be used for assembly and operation. A preliminary estimate has been made and is shown as parametric depth-dose data based on the integral spectral environmental data derived from References 5, 6, and 7. B. PARAMETRIC DEPTH DOSE DATA The preliminary analysis which generates the parametric radiation dose data (Ref. 8) is carried out by using the SHIELD radiation transport program (Ref. 9) using the integral spectral data as input. The statistical analysis of solar cosmic protons was obtained from Ref. 10. The preliminary analysis covers geomagnetically trapped protons and electrons, electron-Bremsstrahlung radiation, and solar and galactic cosmic protons in a 500-km 30-degree assembly orbit (LEO) and in the GEO. The radiation-dose data cover a 6-month mission during the solar
Figure 2. Orbital Integration Map 150 to 1000 Nautical Miles Circular Orbit 30 Degree Inclination AP8 Max Solar Maximum Protons Energy LE 10 Mev (Ref. 5)
Figure 3. Orbital Integration Map 150 to 1500 Nautical Miles Circular Orbit 30 Degree Inclination AP8 Min Solar Minimum Protons Energy GE 10 Mev (Ref. 5)
minimum and maximum activity time periods and, in the preliminary study, are restricted to attenuation through spherical aluminum shells of varying thicknesses with a conversion to dose in water at the center of the sphere. The 6-month parametric data of dose versus aluminum thickness span a range of dose levels that would encompass specific dose criteria set for SPS missions. Figures 4 and 5 present the radiation attenuation data for 500 km, 30 degree circular LEO during solar minimum and maximum activity time periods respectively. It is noted that the most damaging radiation affecting the occupational health for this orbit is due to trapped protons, and in particular during the solar minimum time period. This is due to the fact that during solar maximum period the lower Van Allen Belt has fewer trapped protons due to atmospheric interaction with the low part of the belt at this time compared to the solar minimum period. For GEO, the radiation attenuation data for both solar maximum and minimum activity periods are presented in Figure 6. It is noted that for thin-walled space vehicles the most deleterious radiation would be from trapped electrons. However, on incidence of a solar flare, the flare proton dose predominates for wall thicknesses greater than 2 1 gm/cm of equivalent aluminum. The solar flare protons are reported for both the solar minimum and maximum activity periods (Ref. 10). The 90% confidence level reported represents solar cosmic protons received from a statistical sampling of many larger flares of the past solar cycle and means that at the 90% confidence level no greater fluence of protons, with the spectral rigidity of the sample, would be received in the defined mission time. Other confidence levels could be used for the design criteria (e.g., 99% or 99.9%) but with a significant increase in proton fluence, hence dose, of approximately an order of magnitude (factor of 10). However, since the SPS operations are Earth orbiting and not deep space manned missions with limited alternative evasive moves possible, it is reasonable to use the lower total proton fluences (90% confidence level) with the potential of replacing the crew when and if they have received several large flares, thus shortening their mission life in space.
Figure 4. Computed Radiation Dose - 500 km - 30° Orbit - Solar Minimum Period Attenuation Through Aluminum, Dose in H^O Tissue Equivalent (Refs. 8, 9)
Figure 5. Computed Radiation Dose - 500 km, 30° Orbit - Solar Maximum Period Attenuation Through Aluminum, Dose in H^O = Tissue Equivalent (Refs. 8, 9)
Figure 6. Computed Radiation Dose - 18000 Nautical Miles, 0° Synchronous Orbit Attentuation Through Aluminum, Dose in 1^0 s Tissue Equivalent (Refs. 8, 9)
C. RADIATION DOSE LIMITS The radiation dose in Figures 4, 5 and 6 is point dose at the center of the spherical aluminum shell with 4tt steradian solid angle reception. This can be considered tissue equivalent dose to the skin by dividing by 2 for 2tt steradian reception. Proper shielding of the occupational environment must be achieved in order to be consistent with the radiation protection guides and constraints. Table 9 shows the allowable radiation dose limits for manned spaceflight in Skylab, Shuttle and space station/base programs (Ref. 11) and may be used as preliminary radiation protection guides and constraints for the SPS system. 1. May be allowed for two consecutive quarters followed by 6 months of restriction from further exposure to maintain yearly limit. 2. These dose and dose-rate limits are applicable only where the possibility of oligospermia and temporary infertility are to be avoided. For most manned spaceflights, the allowable exposure accumulation to the Germinal Epithelium (3 cm) will be the subject of a risk/gain decision for the particular program, mission, and individuals concerned. Table 9. Radiation Exposure Limits and Exposure Rate Constraints for Unit Reference Risk (Ref. 11) Biological Dose Through Specified Thickness, (REM) Bone Skin Eye 2 Testes Exposure Period (5 cm) (0.1 cm) (3 mm) (3 mm) 1-year avg. daily rate 0.2 0.6 0.3 0.3 30-day maximum 25 75 37 13 Quarterly maximum^ 35 105 52 18 Yearly maximum 75 225 112 38 Career limit 400 1200 600 200
The occupational health effects of exceeding the guidelines may have various consequences, depending on how far the guidelines have been exceeded, such as nausea, vomiting and fatigue, diarrhea, reduction in lymphocytes and neutrophils, hemmorhage, inflammation of mouth and throat, fever and death. Once the allowable dose limit is set, the minimum equivalent aluminum shell thickness can be determined by reading from Figures 4, 5, and 6. Note that for the same allowable dose limit the shielding thickness required for GEO is about an order of magnitude higher than that required for LEO. Radiation in a space vehicle can be reduced below the levels shown in Figures 4, 5, and 6 by using a sandwich method fusing different metals; i.e., aluminum and lead. Sandwich metal walls will work to lower the Bremsstrahlung radiation as well as to lower the overall radiation as compared to straight aluminum. The drawback is in the weight problem of the metals. A great deal more research and development into the makeup of the walls of the various spacecraft will be necessary. This will be needed to determine the dose to a space worker on his long-term stay (perhaps 6 months) in space. Also, a designed ’’storm cellar” will be needed for any time there is a solar flare. This is needed to survive the storms due to the large increase in radiation. A ’’storm cellar" would have extremely thick walls and give the personnel the protection needed.
Section VI RECOMMENDATIONS A number of areas discussed in this report need to be looked at in greater depth. The following items are the author’s recommendations for future studies of the occupational health effects: (1) A better definition of the SPS design is needed to fully assess the needs of the program. (2) Additional work is needed to make a comparative assessment of the SPS to other types of power plants (i.e., Ground Solar, Coal, Nuclear; Ref. 12). (3) The area of space assembly, fabrication, etc., needs a great deal more research and development. We have very little information in this area and it is not possible to correctly assess it at this time. (4) The subject of microwave radiation is quite open. The standard is being challenged and the outcome will affect SPS design, particularly in the area of the rectenna site. This area is affected by the size of buffer zone required around the rectenna site to protect personnel from the side-lobe radiation. If the standard is changed then the amount of area required for the buffer zone will reflect the change. Microwave standards also affect public health as well as SPS workers. (5) Space radiation is another area of problem to the space workers. The radiation is present 24-hours a day, and the recurrent hazard of the solar flare makes a ’’storm cellar” a real need in an SPS. (6) More research is needed to build, test and evaluate sandwich walls for spacecraft as it is a way to lower the radiation striking the space worker. The balance between weight versus shielding and cost will need to be studied.
REFERENCES 1. "Initial Technical, Environmental and Economic Evaluation of Space Solar Power Concepts," Lyndon B. Johnson Space Center, Houston, TX, August 31, 1976. 2. Livingston, F. R., Baker, L. R., Poon, P. T.-Y., and Kuo, T.-J., Satellite Power System (SPS), Preliminary Resource Assessment, Report 900-805, Rev. A., Jet Propulsion Laboratory, Pasadena, CA., Aug. 7, 1978. 3. Occupational Injuries and Illnesses in the United States, Industrial, 1973, Bulletin No. 1871, Bureau of Labor Statistics, U. S. Department of Labor, Washington, D. C. 4. Dickinson, R. M., Satellite Power System (SPS) Microwave Subsystem Impacts and Benefits, Report 900-800, Jet Propulsion Laboratory, Pasadena, CA., September 28, 1977. 5. Sawyer, D. M., and Vetti, J. I., AP-B Trapped Proton Environment for Solar Maximum and Solar Minimum. NSSDC/WDC-A-R&S 76-06, NASA Goddard Space Flight Center, May 1976. 6. Teague, M. J., Chan, K. W., and Vetti, J. I., AE-6 A Model Environment of Trapped Electrons for Solar Maximum. NS SD C / WDC - A- R&S 76-04, NASA Goddard Space Flight Center, Greenbelt, MD., May 1976. 7. A Model of the Trapped Electron Population for Solar Minimum, NSSDC 74-03, TM-X69909, National Aeronautics and Space Administration, Washington, D.C., April 1974. 8. Koprowski, E. F., Space Radiation Dose for Space Power System Study, Memo 3530-077-031, Jet Propulsion Laboratory, Pasadena, CA., March 28, 1977. 9. Davis, H. S., and Jordan, T. M., Improved Space Radiation Shielding Methods, TM 33-765, Jet Propulsion Laboratory, Pasadena, CA., March 1, 1976. 10. Yucker, W. R., Statistical Analysis of Solar Cosmic Ray Proton Dose, MDC G0363, McDonnell Douglas Corporation, June 1970. 11. Rose, R. G., Radiation Dose Limits for Manned Space Flight in Skylab, Shuttle, and Space Station/Base Programs, Memo on Radiation Constraints, National Aeronautics and Space Administration, Washington, D.C., January 15, 1971. 12. Poon, P., and Baker, L., Assessment of Occupational Health Impacts in the Material Acquisition Phase and Construction Phase of Three Types of Power Plants, Memo 3530-76-012, Jet Propulsion Laboratory, Pasadena, CA., May 26, 1976.
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