Satellite communication is the use of artificial satellites to provide communication links between various points on Earth. These relay stations in the sky have revolutionized global telecommunications by overcoming the limitations of ground-based communication, such as the Earth's curvature and physical obstacles.
This is the key concept for this topic (SLO P-11-B-16).
Weightlessness occurs when apparent weight = 0, i.e., when there is no contact/normal force between the object and its support.
A satellite in circular orbit is in a state of continuous free fall. Gravity provides the centripetal force that keeps it in orbit:
Because the satellite is falling freely toward Earth (while simultaneously moving forward fast enough to keep missing it), every object inside the satellite is also falling at exactly the same rate.
Consider an astronaut of mass standing on the floor of an orbiting satellite:
Key Point: Gravity is NOT absent in orbit. At an altitude of ~400 km (ISS orbit), — about 89% of surface gravity. Weightlessness is caused by free fall, not by the absence of gravity.
If a lift cable breaks and the lift falls freely under gravity, a person inside feels weightless for the same reason: both the person and the lift accelerate downward at , so the floor exerts no normal force. The satellite is simply a "lift" that never hits the ground because it moves forward fast enough.
The vast majority of communication satellites are placed in a geostationary orbit (also called a geosynchronous equatorial orbit).
A single geostationary satellite can see and provide coverage to a vast area of the Earth's surface.
The process involves a simple uplink/downlink system:
Communication satellites operate using microwaves because:
Satellites are powered by large solar panels that convert sunlight into electricity, stored in rechargeable batteries for use during Earth's shadow (eclipse).
The International Telecommunications Satellite Organization (INTELSAT), formed in 1964, operates a large fleet of satellites providing television broadcasting, corporate networks, and mobile communications worldwide. Modern INTELSAT satellites operate at microwave frequencies (4, 6, 11, and 14 GHz) and can handle tens of thousands of two-way telephone circuits and multiple TV channels simultaneously.
| Condition | Normal Force | Apparent Weight |
|---|---|---|
| Stationary on Earth | ||
| Lift accelerating upward | ||
| Lift accelerating downward | ||
| Free fall / Orbit | (weightless) |