# Orbit

## Hill’s Equations: Derivation and Solution Explained

Hill’s equations are equations that describe the relative motion of the chaser object to the target object in the rendezvous of spacecraft. In this article, the meaning and derivation of Hill’s equations and the derivation of the Clohessy-Wiltshire (C-W) solution are explained. What is Hill’s equations? Rendezvous is a maneuver that brings closer a spacecraft …

## Two-Line Element Set (TLE): Format Overview

To calculate the position of the object around the earth, for example, satellites and space debris, we need information on the orbital parameters which describes the shape and size of the orbit. Two-Line Element Set is one of the data formats for describing the orbital parameters. In this article, we explain TLE and its format …

## TLE Epoch to Date

TLE Epoch in the form of NNNNN.NNNNNNNN Date in ISO format

## Earth Centered Inertial Frame (ECI)

Earth Centered Inertial Frame (ECI) is the coordinate system that places the origin at the center of the earth, the x-axis to the vernal equinox, the z-axis to the north pole, and the y-axis as a right-handed system. This coordinate system does not rotate against the Earth’s rotation, thus this system can be regarded as …