FUNCTIONAL BLOCKS OF SATELLITE COMMUNICATIONVishal Patil Milind Vaidya

POWER SUBSYSTEM:(MATERIALS USED)

●SOLAR CELL:●It Converts light (Sun Light) into Electricity.

Features :●They have less efficiency about 10%.●It requires continuous sunlight for the generation of power.

Main use:●It provides DC power and regulated secondary supply voltages for satellites● voltages range 5v to 15v.

SOLAR ECLIPSE CONDITION FOR SATELLITES:

●What is solar eclipse?

●Eclipse condition :The sun light gets cut off and the solar cell power gets cut.

● Then during this period of time Back up batteries are used to generate power at that time.

●Hence storage battery must be capable of providing continues power for more than 12 hours.

●Amplifiers and DC to DC convertors are required.

TELEMETRY TRACKING & COMMAND(TT&C)

●The Telemetry, Tracking and Command subsystem provides vital communication to and from the spacecraft & allows to manage or monitor satellites from ground ●They use entirely different communication channel. ●They consist of various sensors for various parameters

TT&C FROM GROUND STATION

TELEMETRY SUBSYSTEM 1.Sensors & Transducers measures……●Internal voltage ,Currents ,Temperature●Fuel level, Pressure, Power supply●Positional & orientation information●Environmental information magnetic field

radiation

2.Telemetry Encoder Multiplexes various analog & digital information

& modulate before transmission

3.Transmitter It will transmit modulated information through

Telemetry antenna (Omni-directional)

SATELLITE TRACKING SYSTEM

●It uses frequency scanning effect●satellite signals transmitted from a satellite via an antenna mounted on a moving body are analyzed to acquire a position of the satellite●the acquired position of the satellite is continuously tracked, thereby smoothly receiving the satellites signals

COMMAND

●Receiver : Demodulation

● Command decoder: decodes the encoded command signals with special techniques for security & convert it to appropriate pulses

●Driver amplifier: Amplification Then these signal used by satellite for execution

COMMUNICATION CHANNEL SUBSYSTEM:

●Satellites are build to communicate.

●A transponder is used in satellites before transmitting the signal to earth station.

●Transponder: An automatic device that receives, amplifies, and re-transmits a received signal on a different frequency.

TRANSPONDER TRANSPONDER CONSIST OF….

●Filter●Low Noise Amplifier (LNA)●Band pass filter●Mixer plus Local Oscillator●Another Band pass filter and●Power amplifier.

BLOCK DIAGRAM OF TRANSPONDER: Power amplifiers like TWT are used for generating the required

●It Provides necessary gain & output power required for transmitting back to earth station.

●Advantages (TWT):●High gain ●High efficiency●Light weight●Reliable and consistent.

●In the recent years TWT have been replaced by Solid Power Amplifier.

●Multiple channels are used for greater reliability.

●Now days advance transponders demodulate and re-modulate with another using another specific modulation

ATTITUDE CONTROL SUBSYSTEM:

●Satellite attitude is the orientation of satellite with respect to earth.

●Attitude control sub-system provides stabilization in orbit and senses the change in orientation of satellite.

●With built in jet thruster it makes the necessary corections to the altitude of satellite.

●When this subsystem senses the change In position of satellite from the desired position it receives the command and control system and that fires the appropriate thruster at proper time.