Gravity and Orbits

   In the last four hundred years, we have perfected our understanding of the nature of planetary orbits. Johannes Kepler used Tycho's excellent observations to analyze the orbit of Mars. With this work, he managed to explain how the planets orbit the Sun. What he did not know at the time, was that the behavior of the planets had a physical basis. It took the work of Isaac Newton to give mathematical rigor to the field of celestial mechanics.

    Here is what the solar system looks like.

   The same basic rules which determine the orbits of the planets also allow us to send artificial satellites in orbit around the Earth. Today there are thousands of objects orbiting the Earth. The big problem is, we must get the object moving at 7.9 kilometers per second in order to achieve low Earth orbit. And we must reach a velocity of at least 11.2 kilometers per second in order to escape from Earth's gravitational influence. This velocity is, appropriately enough, called escape velocity.

    Let's try to put a satellite in orbit around the Earth.

    Here are some java applets that show you how to get from one planet to another.

    If you want to get to Mars, you have to know about pork chops. And now it's time to plan our trip to somewhere out there. Folks, this IS rocket science!

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Updated October 1, 2009