Key Concepts: Satellite Motion

Satellite Fundamentals

• A satellite stays in orbit because gravity provides centripetal force — it's in continuous free fall around Earth.
• Orbital speed and period depend only on altitude and the mass of the central body.

Types of Satellite Orbits

• Low Earth Orbit (LEO): 200–2,000 km altitude. T ≈ 90 min. Used for ISS, imaging.
• Medium Earth Orbit (MEO): 2,000–35,786 km. Used for GPS satellites.
• Geostationary Orbit (GEO): 35,786 km altitude. T = 24 hours. Used for communications and weather.

Weightlessness

• Astronauts on the ISS feel weightless not because there's no gravity, but because they and the station are in free fall together.
• At ISS altitude (~400 km), g ≈ 8.7 m/s² (about 89% of surface gravity).