Контрольная работа № 8

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1.	Without electrical power, living on the International Space Station wouldn’t be possible. Even the air the crew breathe is created by using electricity to split water molecules. Electricity runs the Station’s air and
	water systems, keeps the lights on, warms meals, and runs computers. It even lets crew members talk to school children by ham radio. Electricity does it all in this home in space.
2.	Supplying reliable electricity to a home 350 km above our planet is a big challenger. Constantly transporting fuel up from the surface would be far too expensive. The most practical solution is sunlight. Fortunately, solar power is plentiful. The trick is to convert the sun’s power into a useful form. Photovoltaic cells are the most practical way to extract power from sunlight in space. The photovoltaic cells are mounted on eight large structures called solar arrays, each measuring 34 metres long and 11 metres wide. The arrays together contain total of 262,400 solar cells and cover an area of about 2,500 m² – more than half the area of an American football field. A computer – controlled gimball rotates the arrays to keep them tilted toward the sun.
3.	But the sun is not always “up”, because the station spends up to 36 minutes in the Earth’s shadow during each 92 minute trip around our planet. During the shadow time the station relies on banks of nickel hydrogen batteries to provide continuous power. Switching back and forth between solar generated power and stored battery power was a challenge for designers of the Station’s power system. The entire electrical power supply has to be switched smoothly twice each orbit, distributing current flow to all outlets and devices.
4.	The result of this carefully managed process is 110 KW of power. After life support, battery charging and other power management uses, 46 KW of continuous electric power are left over for research work and science experiments. That’s enough to run a small village of 50 to 55 houses. Storing and distributing electricity with batteries builds up excess heat that can damage equipment. The heat must be eliminated, so the Station’s power system uses ammonia radiators to dissipate the heat away from the spacecraft.
5.	A second, not so obvious, problem could be dangerous for the astronauts themselves. The Station’s solar arrays carry a strong electric field. At the same time, the Station is zipping through the low-density plasma of the outer regions of the Earth’s atmosphere. A plasma is a gas, filled with charged particles that respond to electric fields-like the ones around the solar arrays. As a result, the hull of the Station becomes highly charged. Space walking astronauts could suffer shocks from touching the metal hull of the Station.
6.	To solve these problems the designers developed devices which neutralize the plasma charge on the hull, and circuit isolation devices, or CIDs, which let a space walking astronauts remove power from selected circuits. Without CIDs, large portions of the Station would have to be powered down during some space walks. Thanks to technological innovations such as
	these, the lights are always shining brightly – and safely – on the International Space Station.