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LESSON 03 OF 6

Orbital Periods (why speed changes)

Beginner ~6 min Slide deck Free

An orbital period is how long a satellite takes to complete one full lap. It's not adjustable — it's locked to the altitude. Higher orbits are slower. This single relationship explains an enormous amount about how space works.

An orbital period is how long a satellite takes to complete one full lap. It's not adjustable — it's locked to the altitude. Higher orbits are slower. This single relationship explains an enormous amount about how space works.

What this lesson covers

Period is altitude-dependent

Kepler's Third Law tells us that orbital period increases with altitude. There's no throttle — a satellite at a given altitude must travel at a specific speed, and that determines the period.

Period at different altitudes

The relationship isn't linear — it follows a power law (period² ∝ semi-major-axis³). Small altitude changes in LEO barely affect the period. The same absolute change at higher altitudes matters much more.

The speed paradox

Here's what catches everyone: to reach a higher orbit you speed up — but end up going slower. A burn adds energy, which raises the orbit. But at that higher altitude, the stable orbital speed is lower.

Key facts

💡At exactly 35,786 km altitude, the period matches Earth's rotation. That's geostationary orbit — the satellite appears to hover over one spot.

Common misconceptions

MYTH

Satellites can speed up or slow down freely

REALITY

Speed is dictated by altitude. To change speed you must change orbit — which costs fuel and changes your altitude.

MYTH

The ISS has engines running constantly to stay in orbit

REALITY

The ISS free-falls around Earth like every other satellite. Its periodic boosts fight atmospheric drag, not gravity.

Altitude dictates speed. Speed dictates period. You can't choose them independently.

This locked relationship is why geostationary orbit exists at exactly one altitude, why LEO satellites lap Earth every 90 minutes, and why 'speeding up' in orbit is the opposite of what you'd expect.

All lessons in Orbit Basics
01LEO vs MEO vs GEO~6 min02Inclination & Ground Tracks~6 min03Orbital Periods (why speed changes)~6 min04Eccentricity (circles vs ellipses)~5 min05Altitude vs Speed (the counterintuitive truth)~6 min06Why GEO "hangs" over one longitude~6 min
← Inclination & Ground TracksAll 6 LessonsEccentricity (circles vs ellipses) →
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