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Space jam

Unlike early satellites that merely bounced off signals, modern satellites receive, amplify, and re-transmit signals to ‘dishes’ across the world. Prakash Chandra tells more.

india Updated: Oct 07, 2007 23:59 IST
Prakash Chandra

You wouldn’t be able to catch sports live on TV, or make that overseas phone call, but for electromagnetic signals bouncing off communication satellites. Isaac Newton thought of satellites as far back as in 1687. But it wasn’t until the development of rockets in the 20th century that it became a reality, when the cold war pitted the erstwhile USSR and the US in a space race. The USSR got there first on October 4, 1957, by orbiting Sputnik 1 the first artificial satellite which we now celebrate as the dawn of the Space Age. The Americans caught up the following year, launching Explorer 1 after a series of failures.

In 1945, sci-fi guru Sir Arthur C. Clarke proposed the idea of geostationary satellites that would allow radio and TV signals to be transmitted around the globe, without the horizon getting in the way. Satellites work on the principle that an object orbits Earth when its horizontal velocity is so high that the ground curves away from it as fast as gravity pulls it down. At sea level, this is around 17,000 mph (but of course you don’t orbit anything at sea level). The higher you go, the lower this velocity and the longer it takes to orbit. At 22,270 miles, a satellite circles Earth every 24 hours at 6,866 mph the same speed as Earth rotates and is called ‘synchronous’. If it also orbits around the equator, it’s ‘geostationary’, because it’s always over the same point on Earth’s surface.

Unlike early satellites that merely bounced off signals, modern satellites receive, amplify, and re-transmit signals to ‘dishes’ across the world. Their optical, microwave, X-ray, and infrared sensors provide information on most everything. Over 1,000 satellites are aloft now, with applications ranging from communications, scientific research, navigation, and reconnaissance, to weather and security. One day, satellites could even harvest electricity from the Sun and beam it down to giant dishes on Earth. Look up on a clear night: there’s every chance you’ll see one of the descendants of Sputnik 1 making its swift, lonely way across the star-filled sky.