Due to the tremendous advantages and uses of laser devices, there are hundreds of institutes in advance countries, which are engaged in developing different types of laser. It is reliably estimated that new lasers are appearing at the rate of one per month. Days are not far away when laser devices will be used as house hold appliances like electrical appliances, one used now a days.
Satellite Communication. Satellite is a body, orbiting a planet. Satellites are natural as well as artificial.
Natural & Artificial Satellites. Natural satellites are those heavenly bodies which move around a planet e.g., moon, whereas artificial satellite are those man-made bodies, which are deliberately made to move around planet e.g., all satellites.
Active & Passive Satellites. Active satellites are those, which have active components like receiver, transmitter and frequency changer etc., e.g., INSAT 1B etc., whereas passive satellites are those metallic bodies which are used to reflect the signal. These do not receive or amplify the signal.
Synchronous & Non-Synchronous Satellites. Synchronous satellites are those, which are synchronised with the earth. These are placed into geo stationary orbit and need not to be tracked. e.g., INSAT 1B, INTELSAT etc., Non-synchronous orbit are those, which are not synchronised with earth. They either move with faster or slower than the speed of earth. They are to be tracked e.g., Spy satellite etc.
Salient Features. The salient features of satellites are as below:
(a) It works on a wide band Communication System.
(b) It has long distance communication range.
(c) Satellite connects one point with many other stations simultaneously unlike co-axial cable or microwave links, which go one point to another.
(d) It is a flexible system, e.g. capacity of channels can be shifted from one geographical area to another on demand.
(e) Operation is almost independent of atmospheric condition.
(f) Signals are almost noise immune and of better quality.
(g) Delay of approximately 600 ms occurs to receive a signal via satellite. This creates echo from ground station to satellite. It is 300 ms roughly.
(h) Signal is subjected to cosmic noise/interference.
Types of Satellite. The following are types of satellites:
(a) Intelsat. Expanded as International Telecommunication Satellite. It facilitates thecommunication between space and ground or region. These are internationally obtained. Mainly belong to Americaand generally channels are hired on loan, e.g., INTELSAT-I, II, III, IV, etc.
(b) Inmarsat. International Maritime Satellite also known as International Maritime Telecommunication Satellite. It provides communication from satellite to ship, mainly suitable for distress calls.
(c) Regional Satellite. This belongs to a particular region, e.g., ARABSAT. It is used for a particular region only.
(d) Domestic Satellite. These are launched by a particular country for their domestic purpose, to provide communication for Radio, TV, Networks, Computers, etc. e.g., INSAT-1B, 1C etc.
(e) Experimental Satellite. These are launched for various experiments e.g., for Meteorological, earth surface experiments, distress in sea, etc. e.g., Aryabhatta, Bhaskara, IRS, etc.
(f) Spy Satellite. These do not revolve in synchronous orbit thus needs tracking. These are utilised for spying purpose (example 1987 movement of Jaguar Sqn was traced next hour by Pakistan).
(g) Junk Eating Satellite. It has two scorplans arms used to collect unwanted garbage existing in geo-stationary orbit.