463 lines
20 KiB
Plaintext
463 lines
20 KiB
Plaintext
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(word processor parameters LM=8, RM=78, TM=2, BM=2)
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Taken from KeelyNet BBS (214) 324-3501
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Sponsored by Vangard Sciences
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PO BOX 1031
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Mesquite, TX 75150
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August 7, 1990
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Courtesy of NASA BBS at 205 895-0028
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T H E S P A C E S T A T I O N
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P O W E R S Y S T E M
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The Space Station represents the commitment of the United States to
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a lasting future in space. This future will be ripe with
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intellectual and technical challenges. It will hold vast opportunity
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for commercial profit and preservation of the nation's economic
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vitality. It will be both a research facility in space and a
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stepping-stone to long-term human space exploration and discovery.
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The Space Station demonstrates that America's significant
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achievements in space lie ahead of us, not behind us. The Station
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also symbolizes our nation's desire to cooperate with others in
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mutually beneficial civil space activities.
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Canada, the European Space Agency, and Japan have already responded
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positively to the U.S. invitation to participate in the development
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of the Station. Formal agreements are being negotiated and are near
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completion.
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If the negotiations are successful, their involvement will lead to
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unprecedented international cooperation, toward the peaceful
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exploration and utilization of the space environment.
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During the early planning stages of the Space Station Program,
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before the first engineer was allowed to set pencil to paper, two
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major questions had to be answered:
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o Who will use the Space Station?
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o What resources will have to be
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provided to those users?
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A detailed survey of the technical community showed that five types
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of experiments would most likely be performed on the Space Station.
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o Observational sciences (astronomy and Earth
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observations)
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o Life sciences
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o Materials sciences
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o Servicing/repair, and
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o Technology development/testing
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Page 1
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The major resources these potential users demanded were found to be:
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o Power
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o Volume
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o Crew time
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The quantitative evaluation of these user requirements defined the
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ground rules for the engineering studies that led to the system
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definition and preliminary design of the Space Station baseline
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configuration.
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____________________________________________________________________
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S P A C E S T A T I O N B A S E L I N E
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C O N F I G U R A T I O N
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Photovoltaic Power Array
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[][][] [][][] High Gain [][][] [][][]
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[][][] [][][] Antenna [][][] [][][]
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[][][] [][][] Radiator \ |{ [][][] [][][]
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[][][] [][][] \ __ ___ |__ [][][] [][][]
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[][][] [][][] ## | |___|J | ## [][][] [][][]
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[][][] [][][] ## |E | |E | ## [][][] [][][]
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|\|\|\|\|\|\|\|\|\|\|\|==|M |___|M |==|\|\|\|\|\|\|\|\|\|\|\|
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[][][] [][][] |__|___|__| [][][] [][][]
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[][][] [][][] | | |H | [][][] [][][]
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[][][] [][][] | |___|M | [][][] [][][]
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[][][] [][][] |__|___|__| [][][] [][][]
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[][][] [][][] / [][][] [][][]
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[][][] [][][] US Laboratory Module [][][] [][][]
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EM = European Module
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JEM = Japanese Experiment Module
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HM = Habitation Module
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____________________________________________________________________
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THE SPACE STATION POWER LEVEL
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Electrical power, in many respects, is the most critical resource
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aboard the Space Station. Electricity is essential to supporting
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human life in space. It allows a multitude of systems on board Space
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Station to operate, support, and produce.
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Whether electricity is used to power life support systems, to run a
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furnace making crystals, to manage a computerized data distribution
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system, or to operate a centrifuge, electricity is the key.
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The more electricity available, the more work possible, and the more
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flexible the entire array of Space Station activities becomes. A
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comfortable amount of power allows men and women to utilize their
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own most precious resources: observation and innovation.
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Page 2
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Adequate power allows a crew, in orbit, and a variety of
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researchers, using telescience capabilities from the ground, the
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opportunity to make instantaneous observations and responses.
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In a severely power-constrained environment, flexibility and
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spontaneity are diminished. This, in turn, limits the invaluable
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utility of a permanent human presence in space.
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In addition, power runs the infrastructure of the hardware and
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software that supports the entire facility. For this reason, Space
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Station power systems and power-level projections have been an
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important focus of attention during Phase A and Phase B definition
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and design stages.
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The power level given as the ground rule in the "reference
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configuration," the starting point for analytical studies during the
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Space Station Concept Definition and Preliminary Design Phase (Phase
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B), was 75 kW with growth capability to 300 kW.
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The Space Station assembly sequence supplied 25 kW of photovoltaic
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power by the second flight. This 25 kW of power would support
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general station-keeping requirements and early payloads that would
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be provided during the assembly phase of the program.
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An additional 50 kW of solar dynamic power was planned downstream in
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the assembly sequence, raising the total power supply to 75 kW, the
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baseline level for the permanently manned phase.
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This figure was based on the projected needs of the future Space
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Station user community and early estimates of the housekeeping
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power.
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A review by Congress of Space Station concluded that the preliminary
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power of 25 kW was insufficient to adequately support early
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payloads.
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As a result, the initial power level was increased to 37.5 kW of
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photovoltaic power. With the addition of the 50 kW of solar dynamic
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power intended for the later stage of the Station development, the
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total power level for the program climbed to 87.5 kW.
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It should be noted that the absence of a permanent crew in such a
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configuration makes crew time the most critical parameter and
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severely limits the kind of experiments that can be performed.
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The Space Station review ordered by the NASA Administrator at the
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end of Phase B resulted in several changes to the Phase B results,
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including a reordering of the assembly sequence to allow for early
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user operation and confirming power at 87.5 kW.
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A subsequent cost review resulted in the "phased" approach to
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construction of the Space Station. Early calculations of power
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needed in this approach yielded 50 kW.
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Further examination of user and housekeeping requirements, however,
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resulted in an increase of that figure to 75 kW for Phase I and an
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additional 50 kW (125 kW total) for a future Phase II.
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Page 3
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THE SPACE STATION POWER SYSTEM
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The only continuously available source of energy in this solar
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system is the Sun. The Sun's energy is available in the form of
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light and heat; however, spacecraft need electricity.
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Accordingly, NASA has pioneered and is continuing to develop
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technologies to efficiently convert the Sun's energy (light and
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heat) into electrical power.
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Some materials, such as silicon and gallium arsenide, can directly
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convert light to electricity. Hence, "solar cells" can be made from
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these materials.
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The efficiency of energy conversion by this method is not very high;
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it ranges from 5 to 10 percent. The cells, however, can be assembled
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into "arrays" and these can be used to generate high power levels.
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In fact, the 75 kW required for the Space Station Manned Base and
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the power for the Polar Platform will be generated entirely by solar
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arrays.
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A spacecraft in orbit around the Earth is not always in direct
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sunlight. Thus, energy has to be stored to provide a continuous
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source of electricity.
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Storage is usually accomplished by using batteries, which is the
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method of choice for Space Station. The Space Station "photovoltaic
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power module" contains both the solar arrays and the batteries.
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____________________________________________________________________
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SPACE STATION PROGRAM
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S O L A R P O W E R O P T I O N S
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(PHOTOVOLTAIC)
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Sunlight
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v v v
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_________
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|_________| Solar Cell
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\ \
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| Direct Current (DC)
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| Electrical Power
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__________ | ___________
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| Battery | | Power |
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|__________| | Converter |
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|___________|
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\ \
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Alternating Current (AC)
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Electrical Power
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(SOLAR DYNAMIC)
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Receiver/Thermal Storage
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\ ______
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| | Sunlight
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__________| | /
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| ' /
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| ' /
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v ' /
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| ' /
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| \_____|/____/ Mirrors
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| ______________________
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|________| |
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| Turbine/Generator |
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|______________________|
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\ \
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Alternating Current (AC)
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Electrical Power
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____________________________________________________________________
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The photovoltaic power system is well understood and has the
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advantage of being off-the-self technology. Its disadvantage is the
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large size of the arrays required to generate sufficient power.
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In addition, the large weight and relatively short lifetime (about
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five years) of the batteries is a disadvantage.
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The Space Station will operate in low Earth orbit (about 220
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nautical miles). In this, or any other near-earth orbit, there is a
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certain amount of "drag," i.e. resistance to the progression of the
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spacecraft.
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As a consequence, the spacecraft tends to slow down. This results
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in a loss of altitude, a gradual progression towards an ultimate de-
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orbit.
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To prevent the Station from eventually reentering the atmosphere,
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periodic reboost of the spacecraft is necessary. This requires a
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resupply of propellant: the larger the area, the larger the drag,
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and the more reboost propellant is needed.
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Resupply of the propellant is needed. Resupply of the propellant is
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part of the life-cycle cost.
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Decreasing the area of the spacecraft minimizes drag. The largest
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area of the Space Station is the solar arrays. Early design concepts
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indicated that a reduction in the area of solar arrays represented
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life-cycle cost reduction.
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However, a newer design concept has mitigated the increased life-
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cycle costs associated with reboosting, by using a hydrogen fuel
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obtained from surplus supplies of water. Therefore, the size of the
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solar array no longer drives life-cycle costs as directly.
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Another source of life-cycle cost is the need to replace the
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batteries after five years. The use of a long-life energy storage
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system represents life-cycle cost savings.
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A solar dynamic power system might provide a solution for these
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problems. This technology, far different from the photovoltaic
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system, utilizes the Sun's heat instead of its light for the
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production of power.
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Heat is collected in the focal point of a mirror. Power is then
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generated exactly the same way as on an earthbound power station: by
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heating a fluid, which in turn rotates a turbine.
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Since a heat/gas-driven turbine is a much more efficient power
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converter than a sunlight-driven solar cell, the mirror (the largest
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part of the solar dynamic system) would have to be only one-fourth
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the area of a solar array to generate the same amount of power from
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the Sun's light.
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There are several different engines that can be used for the
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generation of power within the solar dynamic system. They are
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similar in that they are "closed cycle," i.e., they recycle the
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working fluid. These engines are usually known by the names of
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their inventor. For use on Space Station, the Brayton Cycle engine
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has been selected.
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The energy storage device used for a solar dynamic power system is
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superior to a photovoltaic system because heat is stored rather than
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electricity. Heat is cheaper and far more simple to store for
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subsequent use.
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Storage can be accomplished by taking advantage of the heating, or
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fusion, of inorganic salts. On the sunny side of the Earth, heat is
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absorbed by the salt and it melts. On the dark (cold) side the salt
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freezes and gives up its heat to the working fluid of the engine,
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ensuring continuous operation.
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S U M M A R Y
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An abundant supply of power is one of the top priorities for users
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of the Space Station and therefore, of highest priority for the
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Space Station Program.
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It was for this reason that the original "hybrid" power system was
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chosen: it provided early power to the user by using off-the-self
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photovoltaic/battery technology, then adding the more "growable,"
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but higher risk, solar dynamic system later. This concept was
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revised in light of budget realities. By using only photovoltaic
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modules in Phase I, NASA will be able to meet budget restrictions
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without sacrificing the needs of the users.
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The ability to utilize solar dynamic systems with lower life-cycle
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cost will be added in the future as the Space Station evolves.
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Page 6
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SOLAR POWER OPTIONS: ADVANTAGES DISADVANTAGES
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--------------------------------------------------------------------
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Photovoltaic o Large Data Base for o Limited Data on
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Small Rigid Arrays Hi Voltage Arrays
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with Batteries
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o Tolerant of Pointing o High Life Cycle
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Errors Cost
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o Flexible Array o Development Risks
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Demonstrated Large Array &
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Energy Storage
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o Technology Well o Large Drag Area
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Understood
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--------------------------------------------------------------------
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Solar Dynamic o High Efficiency o Limited Phase
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Change Data
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o Terrestrial Data o High Development
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Base Cost Than
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Photovoltaic
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o Low Life Cycle Cost o More Sensitive to
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--Low Drag Area Pointing Error than
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--Low Production PV Cost
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o Not Demonstrated in
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Space
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--------------------------------------------------------------------
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Hybrid o PV Power for Early o Requires
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Development Station Buildup
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and Logistics
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Support of Both
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Systems
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o SD Low Cost Power as
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Requirements Increase
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o Low Life Cycle Cost
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o Diverse Power Sources
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THE SPACE STATION POWER SYSTEM, NASA
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--------------------------------------------------------------------
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If you have comments or other information relating to such topics as
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this paper covers, please upload to KeelyNet or send to the Vangard
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Sciences address as listed on the first page. Thank you for your
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consideration, interest and support.
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Jerry W. Decker.........Ron Barker...........Chuck Henderson
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Vangard Sciences/KeelyNet
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--------------------------------------------------------------------
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If we can be of service, you may contact
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Jerry at (214) 324-8741 or Ron at (214) 484-3189
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