| Electrical System Of The International Space Station |
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The electrical section is the most critical resource for the International Space Station because it allows the crew to live comfortably, to safely operate the station, and to perform scientific experiments. One method of harnessing Solar Power , called Photovoltaic s, uses purified Silicon Solar Cell s to directly convert Light to Electricity . Large numbers of cells are assembled in arrays to produce high power levels. The process of collecting sunlight, converting it to electricity, and managing and distributing this electricity builds up excess heat that can damage spacecraft equipment. This heat must be eliminated for reliable operation of the Space Station in orbit. The ISS power system uses Radiator s to dissipate the heat away from the spacecraft. The radiators are shaded from sunlight and aligned toward the cold void of deep space. SOLAR ARRAY WING Each ISS Solar Array Wing (often abbreviated "SAW") consists of two retractable "blankets" of solar cells with a mast between them. Each wing uses nearly 33,000 solar cells and when fully extended is 115 feet (35 m) long and 38 feet (12 m) wide. 1 When retracted, each wing folds into a Solar Array Blanket Box just 20 inches deep. 2 The completed ISS will have eight solar array wings. 3 BATTERIES Since the station is often not in direct sunlight, it relies on nickel-hydrogen (SS/L), under contract to Boeing . {Link without Title} POWER MANAGEMENT AND DISTRIBUTION The power management and distribution subsystem disburses power, as of December 30 , 2005 , at 160 volts of Direct Current (abbreviated as "DC") around the station through a series of switches. This voltage may change as the Solar Arrays degrade over time and the Solar Arrays' Voltage-Max-Power (''V''mp) point changes. This ''V''mp is the operating voltage at which the arrays provide the most power. The switches that route power throughout the station have built-in microprocessors that are controlled by software and are connected to a computer network running throughout the station. SSU Eighty-two separate strings, or power lines, lead from each solar array to a Sequential Shunt Unit (SSU) that provides coarse electrical power regulation. The job of the SSU is to shunt, or short, the excess current from the solar array to maintain the desired 160 volt bus voltage. 4 The SSUs are provided by SS/L . DC-to-DC conversion To meet operational requirements, DC-to-DC converter units step down and condition the voltage from 160 to 124.5 volts DC to form a secondary power system to service the loads. By transmitting power at higher voltages and stepping it down to lower voltages where the power is to be used, much like municipal power systems, the station can use smaller wires to transmit this electrical power and thus reduce launch loads. The converters also isolate the secondary system from the primary system and maintain uniform power quality throughout the station. STATION TO SHUTTLE POWER TRANSFER SYSTEM See Also: Station-to-Shuttle Power Transfer System The Station-to-Shuttle Power Transfer System (SSPTS) has been installed on Pressurized Mating Adapter -2 (PMA-2), which is located at the forward end of the ''Destiny'' laboratory where shuttles dock. The SSPTS will allow visiting shuttles to derive power from the station to extend their missions. 5 SEE ALSO REFERENCES
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