Anatomy of a satellite courtesy of TechMuseum

A satellite is a complex machine. All satellites are made up of several subsystems that work together as one large system to help the satellite achieve its mission. This simplified illustration shows the key parts of a remote-sensing satellite. The main subsystems are grouped by color.

Command and Data

The Command and Data Handling system controls all the functions of the spacecraft. Its like the satellite's brain. The heart of this is the Flight Computer. There is also an Input/Output Processor that directs all the control data that moves to and from the Flight Computer.

All working satellites need power to operate. The Sun provides power to most of the satellites orbiting Earth. This Power System uses solar arrays to make electricity from sunlight, batteries to store the electricity, and distribution units that send the power to all the satellite's instruments.

Pointing Control

The Pointing Control system keeps the satellite steady and pointing in the right direction. The system uses sensors, like eyes, so the satellite can "see" where it's pointing. The satellite also needs a way to move into its proper position, so the system has a propulsion mechanism or momentum wheels. The type of pointing control a satellite needs depends on its mission. A satellite making scientific observations needs a more precise steering system than a communications satellite does.

Mission Payload

The Payload is all the equipment a satellite needs to do its job. It's different for every mission. A communications satellite needs large antenna reflectors to send telephone or TV signals. An Earth remote sensing satellite needs a digital camera and image sensors to take pictures of the earth's surface. A scientific research satellite needs a telescope and image sensors to record views of stars and other planets.

Communications

The Communications system has a transmitter, a receiver, and various antennas to relay messages between the satellite and Earth. Ground control uses it to send operating instructions to the satellite's computer. This system also sends pictures and other data captured by the satellite back to engineers on Earth.

Thermal Protection

The Payload is all the equipment a satellite needs to do its job. It's different for every mission. A communications satellite needs large antenna reflectors to send telephone or TV signals. An Earth remote sensing satellite needs a digital camera and image sensors to take pictures of the earth's surface. A scientific research satellite needs a telescope and image sensors to record views of stars and other planets.

Solar Cells
(NASA)

Solar cells are a special class of semiconductors that convert sunlight into electricity. They do this without pollution, noise, or moving parts. Solar cells or PV cells rely on the photovoltaic effect to absorb the energy of the sun and cause current to flow between two oppositely charge layers.

The photovoltaic effect was first reported by a French scientist Edmund Becquerel in 1839. He observed a voltage between two electrodes in a beaker of electrolyte when the beaker was exposed to sunlight. This led him and other 19th century scientist to search for an explanation for this effect.

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