1. Historical Perspective
Orbital Mechanics
Historical Perspective
Aerospace Engineering
© 2011 Project Lead The Way, Inc.

2. What Is an Orbit?
Orbit refers to the motion of one body around another
Although not always the case, one object is typically very large in relation to the other
In this case, the smaller object is said to orbit around the larger, and the larger is typically presumed to be fixed in space

3. What Is a Satellite?
Today we typically think of a satellite as something human-made that orbits the Earth
This is true, but anything that orbits another body is a satellite
The planets in our solar system are satellites of the Sun
The Moon is also a satellite of the Earth

4. History of the Study of Orbital Mechanics – Ancient Greece
Interest in orbital motion dates at least to ancient Greece
Aristotle studied the motion of the planets in the night sky
General understanding at the time was that the Earth was fixed in space and the heavenly bodies moved around it

5. History of the Study of Orbital Mechanics – Copernicus
Nicolaus Copernicus ( )
First to theorize that the Earth and other planets actually revolved about the Sun
Assumed the motion to be circular
Took accurate measurements and found that his assumption was not strictly accurate
Theory was considered heretical at the time

6. History of the Study of Orbital Mechanics – Brahe
Tycho Brahe ( )
Lectured at University of Copenhagen
Responsible for gathering a wealth of accurate planetary motion measurements

7. History of the Study of Orbital Mechanics – Kepler
Johannes Kepler ( )
Assistant to Brahe
Proposed that planetary orbits were elliptical
Proposed laws of orbital motion that are still used today

8. History of the Study of Orbital Mechanics – Hooke
Robert Hooke ( )
Member of the Royal Society
Debated Newton on facts about orbital mechanics

9. History of the Study of Orbital Mechanics – Newton
Isaac Newton ( )
Grew interested in mathematics from reading about astronomy
From Kepler’s work, deduced the existence of an inverse square law attractive force
Proposed Theory of Universal Gravitation
Wrote Principia, considered the greatest scientific book ever written
Posits his three laws

10. Conclusion Interest in orbital motion dates back to ancient history
First formal assertion that the Earth was not the center of all things in mid-16th century
Study of orbital motion led directly to Newton’s Principia and the three laws

11. Conclusion
Study of orbital motion from 16th century until Newton focused on how the planet orbited the Sun
Newton proposed why the planetary orbits exhibit the behavior they do with the Theory of Universal Gravitation
Kepler’s and Newton’s laws govern our understanding of orbital mechanics still today