Isro.Us | Space Exploration

The Indian National Satellite (INSAT) system which are placed in Geo-stationary orbits is one of the largest domestic communication satellite systems in Asia-Pacific region. Established in 1983 with commissioning of INSAT-1B, it initiated a major revolution in India’s communications sector and sustained the same later. INSAT space segment consists of 21 satellites out of which 11 are in service (INSAT-2E, INSAT-3A, INSAT-3B, INSAT-3C, INSAT-3E, KALPANA-1, GSAT-2, EDUSAT and INSAT-4A, INSAT-4B, INSAT-4CR)

The system with a total of about 211 transponders in the C, Extended C and Ku-bands.provides services to telecommunications, television broadcasting, weather forecasting, disaster warning and Search and Rescue operatilons.

GSAT Series

GSAT-4, also known as HealthSat, was an experimental communication and navigation satellite launched in April 2010 by the Indian Space Research Organisation on the maiden flight of the Geosynchronous Satellite Launch Vehicle Mk.II rocket. It failed to reach orbit after the rocket's third stage malfunctioned. The third stage was the first Indian-built cryogenic-fuelled upper stage, and was making its first flight. The ISRO suspects that the failure was caused by the third stage not igniting.

The GSAT satellites are India's indigenously developed technologies of satellite communications, like digital audio, data and video broadcasting. GSAT has been designed with two S-band and 3 C-band transponders (a high power C-band and two indigenous C-band transponders).

• Plasma Thrusters

  In order to prevent a satellite from thus getting lost, small engines are fitted in and these can be fired by signals from Earth. When a satellite begins to go astray, its trackers on Earth fire one of these engines to nudge it back in line. But once these engines run out of fuel, the trackers can't do this and the satellite goes out of control. Therefore, the fuel these engines contained determines the life of the satellite.

  Typically, in a satellite, half the space is occupied by these engines, leaving only the rest for equipment such as transponders or cameras. A plasma thruster is an engine that uses the discharge of plasma to propel an object. Plasma is a gas in which some electrons have been ripped off their atoms by the application of external energy. These electrons and the (remainder) ions co-exist, and this state is often referred to as the fourth state of matter, after solid, liquid and gas. Plasma exists everywhere. The sun, for instance, is a huge chunk of plasma.

  Plasma, electrically charged gas, is influenced by magnetic field. In a plasma thruster (to put it in very simple terms), you create a magnetic field, with the help of which you can direct a jet of plasma out through a nozzle. A thrust, in the opposite direction, results.

  Plasma thrusters are nothing new. They have been used off and on, even as early as the 1960s. There seems to be some resurgence in interest in them now.

GSAT-4

The GSAT-4 was a little different. Instead of conventional chemical engines, it had four ‘plasma thrusters.' Because of this, the life of the satellite would have been seven years, instead of 4-5. At optimum use, these plasma thrusters could enhance the life of a satellite to even 15 years.

The GSAT-4 satellite had four of these thrusters – two made by Russians and two ‘made in India'. Satellites launched by ISRO in future may be expected to use plasma thrusters for maintaining ‘attitude', or orientation. These thrusters last much longer than the chemical rockets used today, as they are powered by electricity that the solar panels generate from sunlight. Consequently, not only will the satellites live long. Also, more on-board space will be freed for instruments.

The GSat-4 would have been a good learning experience. Hmm, it's already gone!