Orbital Energy and Speed

Orbital Energy

Every orbit has a specific amount of energy, made up of two parts:

Kinetic Energy: Energy from motion (speed) Potential Energy: Energy from position (altitude)

These trade back and forth as you orbit: - Low in orbit → moving fast → high kinetic, low potential - High in orbit → moving slow → low kinetic, high potential

Total energy stays constant (unless you use your engines)!

The Vis-Viva Equation

This beautiful equation tells you your speed at any point in your orbit:

v² = μ(2/r - 1/a)

Where: - v = your current velocity - μ = gravitational parameter (3.986 × 10⁵ km³/s² for Earth) - r = current distance from planet center - a = semi-major axis (average of periapsis and apoapsis)

This explains everything about orbital speed!

Practical Implications

Understanding energy helps you:

1. Predict speeds: Know how fast you'll be at any point 2. Plan efficient burns: Burn when you're moving fastest 3. Understand orbit stability: Higher orbits need less speed 4. Calculate maneuvers: Know exactly how much delta-V you need

The Oberth effect (burning when fast) comes from this principle!