Geostationary orbit
Gravitational Fields - OCR A-Level Physics
Key Definition
Geostationary orbit
An orbit in which a satellite remains above the same point on the Earth's surface at all times.
An orbit in which a satellite remains above the same point on the Earth's surface at all times.
- A geostationary orbitAn orbit with a periodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s). of exactly 24 hours, directly above the equator, so the satellite remains above the same point on Earth's surface. has three defining properties: periodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s). $T = 24 hours (86400 s)$, orbits in the equatorial planeThe plane perpendicular to the Earth's axis of rotation, passing through the equator., and orbits in the same direction as Earth's rotation (west to east).
- The orbital radius is approximately 42,200 km from Earth's centre (about 35,800 km above the surface).
- Used for communications satellitesSatellites in geostationary orbit used for TV, phone, and internet relay — they remain above a fixed point on the equator. and weather satellitesSatellites (often in polar orbits) used for imaging Earth's atmosphere and weather systems. because they appear stationary relative to ground-based receivers.
- There is only ONE possible geostationary orbital radius (determined by $T = 24 hours$ and M_E).
- Calculating: r = (GMT^2 / $4\pi$^2)$^{1/3}$with T = 86400 s.
Common Mistake
MEDIUM
Wrong: Saying a geostationary satellite is 'not moving' or 'has no forces acting on it'.
Right: A geostationary satellite IS moving (at about 3070 m \(s^{-1}\)) and HAS a force acting on it (gravity provides the centripetal forceThe resultant force directed towards the centre of a circular path that causes an object to move in a circle. It is not a separate force but the net force providing circular motion.). It appears stationary only because it orbits at exactly the same angular velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.The rate of change of angular displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m).. The angle swept per unit time for an object moving in a circle. Measured in rad s⁻¹. as the Earth rotates.
Right: A geostationary satellite IS moving (at about 3070 m \(s^{-1}\)) and HAS a force acting on it (gravity provides the centripetal forceThe resultant force directed towards the centre of a circular path that causes an object to move in a circle. It is not a separate force but the net force providing circular motion.). It appears stationary only because it orbits at exactly the same angular velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.The rate of change of angular displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m).. The angle swept per unit time for an object moving in a circle. Measured in rad s⁻¹. as the Earth rotates.