آموزش زبان انگلیسی ELT
A. Hashemi Mehr 
قالب وبلاگ

   Satellites are tracked by United States Space Surveillance Network (SSN), which has been tracking every object in orbit over 10 cm (3.937 inches) in diameter since it was founded in 1957....


...There are approximately 3,000 satellites operating in Earth orbit, according to the US National Aeronautics and Space Administration (NASA), out of roughly 8,000 man-made objects in total. In its entire history, the SSN has tracked more than 24,500 space objects orbiting Earth. The majority of these have fallen into unstable orbits and incinerated during reentry. The SSN also keeps track which piece of space junk belongs to which country.

The SSN was founded in the wake of the launch of Sputnik, the first artificial satellite, by the Soviet Union in October 1957. Orbiting the planet at 20,000 mph (32,186.88 kph) while emitting a constant radio signal, Sputnik was a red flag that told America not to take its technological dominance for granted. In the following decade, the Space Race between the USSR and USA occurred, ending with Apollo landing in July 1969.

As space technology matured, satellites were launched for military and commercial purposes. The price of satellite launches has dropped to as low as a few million dollars for light satellites, and a few tens of millions for heavy satellites. This put satellite technology within the reach of many nations and international companies.

Satellites have an operating lifespan between five and 20 years. As of 2008, the former Soviet Union and Russia had nearly 1,400 satellites in orbit, the USA about 1,000, Japan more than 100, China about 80, France over 40, India more than 30, Germany almost 30, the UK and Canada 25, and at least ten each from Italy, Australia, Indonesia, Brazil, Sweden, Luxembourg, Argentina, Saudi Arabia, and South Korea. The company Sea Launch — a consortium of four companies from the United States, Russia, Ukraine and Norway — has launched a few satellites into orbit from international waters every year, although the company filed for bankruptcy in 2009.

The largest man-made satellite currently in orbit around the Earth is the International Space Station. Some satellites, called microsats, nanosats, or picosats, can be as small as 10 cm (3.937 inches) in diameter and 0.1 kg (0.22 pounds) in mass.

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