Basic Orbit Changes

The Golden Rule

The most important rule in orbital mechanics:

You change the OPPOSITE side of your orbit

If you burn at periapsis (low point): - Prograde → raises apoapsis - Retrograde → lowers apoapsis

If you burn at apoapsis (high point): - Prograde → raises periapsis - Retrograde → lowers periapsis

This is counter-intuitive but fundamental!

Why This Happens

When you speed up at one point in your orbit, you have more energy. This extra energy carries you higher on the opposite side before gravity slows you down.

Think of a pendulum: when you push it at the bottom, it swings higher on the opposite side.

Similarly, when you slow down, you have less energy and don't climb as high on the opposite side.

Practical Applications

To raise your entire orbit: 1. Burn prograde at periapsis to raise apoapsis 2. Later, burn prograde at the new apoapsis to raise periapsis

To lower your entire orbit: 1. Burn retrograde at apoapsis to lower periapsis 2. Later, burn retrograde at the new periapsis to lower apoapsis

This two-burn technique is the foundation of orbit transfers!