The first satellite

Today the word satellite widely refers to man-made satellites. However, when the German astronomer Johannes Kepler coined the term “satellite” in 1610 , he used it to describe the bodies orbiting Jupiter. The Englishman Sir Isaac Newton was the first to publish a scientific explanation of how to produce a man-made satellite in his Philosophiae naturalis principia mathematica (Mathematical Principles of General Philosophy) which he published in 1686. He imagined a cannonball fired high enough would not fall back to earth, but would start orbiting our planet continuously like a satellite. At this time, it was just a thought experiment based on Newton’s law of universal gravitation. It then took 271 more years to fulfil this dream of a man-made satellite.

The race to space was significantly driven by the Cold War starting after the second world war. The two remaining super powers USA and UDSSR were competing in every field to prove the superiority of their system. Military strength was an important issue. With the invention of the atomic bomb, the development of large carrier rockets were highly prioritised. Two charismatic figures pressed the process of rocket science ahead – Sergey Korolev for the UDSSR and the German Wernher von Braun for America. Both engineers were employed to build rockets for military purposes, but they also saw the capability of using rockets for space travel. However in the beginning aerospace had only minor priority for their governments. A lot of convincing was necessary to get funds for it. For example, when speaking to military audiences, Wernher von Braun emphasised the importance of national defence and beating the Soviets into space; and when speaking to scientists, he exhibited equal and genuine enthusiasm for the exploration of a new frontier.

In the end both parties received the funding and started to work on  satellite programs. The UDSSR was then the first to develop and launch a fully functional satellite into space.

Model of Sputnik I

Model of Sputnik I

Sputnik was the first man-made satellite in space. It was a metallic sphere with four long antennas and contained a built in transmitter to send signals to Earth. Besides that, the hull of Sputnik was very highly polished to promote optical tracking. So the satellite could be determined optically and phonologically (by transforming the transmitted radio signals into sound). Launched on October 4, 1957 it had a tremendous impact. Besides the symbolical importance of this event – as stated, Sputnik was the first man-made object to orbit the Earth – there was also an interesting discovery. The signals that Sputnik emitted could be used to trace the satellite’s position by utilising the Doppler shift*. More importantly it was also possible the other way around. By knowing the satellite’s orbit, which was computed by recording the signals, it was possible to determine the position of the receiver. So Sputnik gave birth to space based radio-navigation systems. Sputnik was a huge success for the Soviet propaganda and started the rearming in space. As with radar in the second world war, this competition again leads to a rapid progress in a completely new technology – aeronautics.

*The Doppler shift (also known as Doppler effect) is a shift in the frequency of a moving transmitter that occurs relative to the observer.

Recorded audio samples of the signals of the first satellites can be found here:

This post was extracted from a paper by Thomas Bornschlegel, The History of the Global Positioning System GPS. The full pdf paper can be seen here.

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