== Two Body Propagator ==

Assume there are only two bodies in space, one is earth and other is your satellite and only gravitational force acting between these two.

[[File:Equation9.gif|frame|center]]

As you might have heard or read that if you throw a ball horizontally from a certain height with the correct velocity then it will revolve around earth. Well this is the same thing. Once you know from where and when you throw the ball, you will get the position of the ball at any instant of time, with these equation of g by integrating it twice with respect to time. This is a very crude model and it doesn’t even generate a sun-synchronous orbit.

== J2 Propagator ==

The fact that earth rotates around its own axis makes it fat around the equator due to centrifugal force acting on it. So it becomes like orange not like a football. The earth’s equatorial radius is 21 km larger than the polar radius. This flattening at the poles is called oblateness (oblateness = [equatorial radius − polar radius]/equatorial radius). <ref>Orbital Mechanics for Engineering Students, Section 4.7, page 177-181</ref> <br \>