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What's Inside a Satellite?

Artist's Conception of Terra Satellite Orbiting Earth
A 21st Century Satellite Orbiting Earth

Most satellites have internal sensors to measure voltages, currents, temperatures and other information on the health of equipment. The measurement data is encoded into a telemetry signal and relayed by transmitter to ground controllers on Earth.

Communications satellites have additional radio transmitters and receivers to send many signals to and from Earth. Observation satellites often have optical and infrared cameras and radar for altitude measurements. Navigation satellites have highly-stable radio receivers and transmitters.

Communications satellites relayed military TV from Somalia in 1992 and later years, while U.S. spysats were moved into position over the Balkans to stare down at the former Yugoslavia.

Many satellites have attitude-control equipment to maintain desired orbits, to point sensors at their targets in space or on the ground, to point radio antennas at ground stations, and to keep solar-power generators pointing at the Sun.

Satellites usually are powered by the Sun, but nuclear-powered electricity generators sometimes are built into spacecraft.

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