DIY Comms and Control for Amateur Space

Chapter 5. Orbits

Defining Orbits

It’s helpful to know where your satellite is, other than saying “up there” or “in orbit.” For Earth-orbiting satellites, their path is a precise, repeating ellipse with one focus at the center of the Earth. An orbit is defined by six parameters, and if you know the value of those parameters, and the time, you can predict exactly where your satellite will be.

A Little Theory

The current movement of anything (orbit or not) can be defined by two terms: its position and its velocity. We live in a three-dimensional world, so we need three coordinates to define its position as x, y, and z. We also need three coordinates to define its velocity—velocity along x, along y, and along z. That’s six coordinates to define ...