Credit: ESA – EDRS-C Satellite

A satellite is a moon, planet or machine that orbits another space object (planet or star).

Moons are natural satellites orbiting planets, planets are also natural satellites orbiting stars (such as earth orbiting the Sun).

An artificial satellite is a man-made machine placed in orbit of the earth, moon, another planet, asteroid or a comet, for a specific mission. This is a semi-independent computer-controlled system.

Artificial Satellites known to us as “Satellites” comes in different sizes and they rotate in different orbits and altitudes depending on its purpose (payload).

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• Space Segment: includes the subsystems or hardware that is sent into a specific orbit in space that carries specific payload for a specified mission. All satellites subsystems are the same, but payloads vary depending on its mission and purpose. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.
• Ground Segment: includes hardware and software for tracking and communicating with the satellite for receiving space signals for further data analysis depending on its purpose.

• Service-bus Module (Mechanics): This is the main structure or body of the satellite including fuel tanks, batteries, main engine and small thrusters.
• Communication Module (Electronics): This is the electrical and communication instruments of the satellite, including antenna, radio transmitters, receivers and solar arrays.
• Payload Module: Refers to the package of sensors and extra electronics that performs the mission of the satellite such as cameras, SAR , MSS , communication transponders.

Over 50 artificial satellites are launched into space every year by space launch vehicles. Types include:

• Navigation satellites (navsats) such as the 32 satellites involved in the Global Positioning System (GPS), used by people in transportation (ships, planes and vehicles) to know where they are and how to get to their destination. 
• Communications satellites (comsats) that receive and send signals such as radio waves and microwaves including phone calls, computer data, TV and radio and internet traffic.
• Weather satellites (meteorological satellites) (meteosats) that measure weather and climate data such as clouds, rain, snow, temperature, air pressure used for weather forecasting and trends.
• Military (Spy satellites) that watch developments  such as missile movements and listen into all kinds of communications.
• Earth observation satellites that measure and photograph earths surface for analysis and monitoring events.
• Space telescopes used to explore space and observe distant planets, galaxies and other astronomical objects.

Satellite categories based on Wet Mass (satellite + fuel)

• Small Satellite (<500 kg)
• Microsatellite (10 kg – 100 kg) 
• Nanosatellite (1 kg – 10 kg)
• Picosatellite (0.1 kg – 1 kg)
• Femtosatellite (< 0.1 kg)

Satellite categories based on Orbit

• Low Earth orbit
• Polar orbit
• Geostationary orbit

SaudiSat 1a, 1b & 1c are microSats, manufactured by KACST & SpaceQuest, launched in 2000 & 2002 by ISC Kosmotras’ Dnepr and carry amateur radio communications payload.