TABLE OF CONTENTS Sometimes it is simplicity which is hidden under what is apparently complex; sometimes, on the contrary, it is simplicity which is apparent, and which conceals extremely complex realities. What is there more complicated than the disturbed motions of the planets, and what is more simple than Newton's law?
- Henri Poincar , Science and Hypothesis
Orbital mechanics is the study of motion of satellites under the complex physical forces that govern them as well as the spacecraft responses to maneuvers. It undergirds many of the models and analyses in this book. Besides satellite motion and maneuvers, this chapter discusses what engineers call operational astrodynamics, which includes observing the satellites in orbit and maintaining accurate state information for such requirements as satellite catalogs and command and control.
As a user of space simulations, you may take orbital mechanics modeling for granted, but it is worth a fuller look. In this chapter I will discuss the choices available for orbital mechanics, how your choices affect the fidelity of simulations, and which simulations benefit from them.
Whenever analysts propagate an orbit (integrate the equations of motion), they are simulating. Whether to model and simulate, control space operations, or maintain the satellite catalog, they select some forces to include in solving the motion. Models of varying precision represent these forces. Analysts also choose solution methods by balancing accuracy against constraints on computer and time resources. The maneuvers used to place satellites in orbit, maintain...
