 Perifocal coordinate system

The perifocal coordinate system is a framework used in orbital mechanics to describe the position and velocity of an object in orbit around a central body, such as a planet or star. In this system, the coordinates are defined relative to the orbital parameters of the body in question. Here's how the perifocal coordinate system is structured: 1. **Perifocal Plane**: The plane in which the orbit lies is called the perifocal plane.