Science & Technology in Action

7th Edition

Space Satellite Physics

Discover Science & Engineering

Ireland is a member of the European Space Agency and, as such, has been involved in many major space projects. Most of us are familiar with the International Space Station which is the largest of the some 3,000 operating satellites currently in orbit. This lesson traces the revolutionary ideas of early scientists such as Galileo and describes how Newton’s Laws are used to calculate orbits.
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Lesson excerpt

Europe in Space
Since its foundation in 1975, the European Space Agency (ESA) has led many major space projects and has cooperated with Russian and US space agencies. At present the ESA has eighteen member countries including Ireland and many Irish companies provide components for satellites and other space craft. At present, there are over 3,000 operating satellites orbiting the Earth. The largest of these is the International Space Station (ISS). None of this would have been possible without a thorough understanding of the laws of motion and gravitation. In this lesson we look at the mathematics behind these laws.

Revolutionary Ideas
In the 1630s Galileo published two major works in which he contrasted a new scientific world view with the traditional view. For example, from the time of Aristotle it was generally believed that motion required aforce. This seems like a reasonable idea which is consistent with our everyday experience. However, it could not explain, for example, why an arrow would keep moving long after it had been fired from a bow.

Galileo carried out many experiments and showed that a forcecauses acceleration – not a steady speed. He also realised thatfriction caused moving bodies to slow down and eventually stop, and proposed that if there were no friction then, once a body was set in motion, it would move forever without the need for further force. This was (and still is) a counter-intuitive idea that many people could not accept. However, we now know that as we reduce friction in machines, less force is needed to keep things moving.

Building on the ideas of Galileo and others, Isaac Newton devised three simple propositions ('laws') to describe how things move. He also proposed an inverse-square law of gravitational attraction, that is the force of attraction between two bodies (such as the Earth and the Moon or the Earth and an apple) was inversely proportional to the square of the distance between their centres; for example, if the distance is doubled then the force is reduced to a quarter of what it was. These revolutionary propositions were published in 1687.

True or False?

  1. A satellite that appears to move is said to be in a geostationary orbit. false
  2. The force of attraction between two bodies is proportional to the cube of the distance between their centres. false
  3. A force causes a mass to accelerate. true
  4. A centripetal force keeps a body moving in a straight line. false
  5. The International Space Station is the largest artificial satellite in orbit. false
  6. Sputnik was the first to be launched into orbit. true
  7. Ireland is a member of the European Space Agency. true
  8. In the absence of any friction, a moving mass would keep moving forever. true