Time and Orbital Period

Orbital Period

Orbital period is the time it takes to complete one full orbit.

Key facts: - Low Earth Orbit (400 km): ~90 minutes - Medium Earth Orbit (20,000 km): ~12 hours - Geostationary Orbit (35,786 km): exactly 24 hours - Moon's orbit: 27.3 days

Notice: Higher orbits take longer!

Why? You're traveling farther, AND moving slower.

Kepler's Third Law

One of the most beautiful laws in physics:

T² = (4π²/μ) × a³

Or more simply: T = 2π√(a³/μ)

Where: - T = orbital period (seconds) - a = semi-major axis (meters) - μ = gravitational parameter

This means: period squared proportional to distance cubed

Double your altitude? Period increases by 2.8×

This law governs everything from satellites to planets!

Practical Applications

Understanding periods helps you:

1. Time transfers: Know when you'll reach apoapsis 2. Plan rendezvous: Match orbital periods with targets 3. Design satellite constellations: Place satellites with specific periods 4. Calculate communication windows: Know when satellites are overhead

Example: Geostationary satellites have 24-hour periods, so they stay above the same spot on Earth!