Geostationary Satellites

A geostationary satellite has the same angular speed as Earth's rotation and stays fixed above one point on the equator.

Concept

Required period: $T = 24$ hours (sidereal day ≈ 23h 56min).

Required orbital radius: From $T^2 = \frac{4\pi^2}{GM}r^3$ ⇒ $r \approx 42164$ km from Earth's centre ⇒ altitude ≈ 35786 km.

Orbital speed: $v \approx 3.07$ km/s.

Plane: Must be in the equatorial plane and prograde direction.

Worked Example

DTH TV satellites, weather sats like INSAT.

Common Confusions

• Geostationary is a SPECIAL CASE of geosynchronous (24-hour period). Geosynchronous can be inclined; geostationary is equatorial only.
• From the satellite's frame, Earth's surface appears stationary.

Key Takeaways

• Period = 24h, altitude = 35,786 km.
• Stays above one longitude on the equator.
• Used for communication, broadcasting, weather monitoring.