Satellite subsystems

Satellites are used for multipurpose applications. They are very much expensive and its launching is a difficult task. The important subsystems of a satellite are power supply system, altitude control system, orbit control system, command system and communication system. The power supply system has three parts-solar array, battery and power supply control unit. Photovoltaic cells are used in solar array which converts solar radiation to electricity. Thousands of such cells are mounted on satellite surface. Altitude control system detects satellite altitude, compares it with the reference axis, determines the corrective torque and corrects the altitude with the help of the actuators mounted on the satellite. Altitude control mechanism adopted differs on the basis of nature of satellite. Spin stabilized satellites and three axis body stabilized satellites employ different control mechanisms. In orbit control system, some sensors are used which measure linear acceleration and velocity changes. Command system which is also known as TT&C system (Telemetry, Tracking & Command) measures angle and range for the localization of the satellite, transmits necessary information and receives command signals. In the communication system, a transponder is used which receives signal and shifts its frequency for transmission.