GSAT’s are experimental satellites which was launched during the first developmental test flight of Geo Synchronous Satellite Launch Vehicle GSLV-D1 on 18 April 2001. It carries two S-band transponders for Digital Audio Broadcast and three Normal C-band transponders to demonstrate new applications including digital sound broadcasting, Internet services, distance education, developmental communications and compressed digital TV services. This is a technologically advanced satellite. The salient features of this satellite are:

1. Fast Recovery Star Sensor which provides enhanced accuracy of measuring satellite orientation and for quick earth-lock recovery in case of loss of lock.
2. New earth sensor using pyro electric detectors.
3. Alternate strategy for orbit raising using a combination of four 22 Newton thrusters.
4. Thermal control using heat pipes.
5. New technique of power management through charger arrays for improving the overall efficiency of power systems.
6. Orbit raising using perigee firing strategy.
7. 10 Newton reaction control thrusters.

The Communication Payload of GSAT-1 consists of three normal C-band transponders, two CXS transponders, the Antenna Positioner Mechanism which can switch the antenna beam between two locations, Digital Video Transmission, Digital Audio Transmission and the Internet Broadcast System.

GSAT-2 is a 1850 kg experimental communication satellite launched on the second developmental flight GSLV-D2 on 8-5-2003. The satellite carries four C-Band transponders, two KU-band transponders and a mobile satellite service payload operating in S-Band and C-Band for forward link and return link respectively. Besides the communication payloads, GSAT-2 carries four piggyback experimental payloads: They are:

1. Total radiation dose monitor to compare the estimated radiation doses inside the satellite with the directly measured radiation doses using a radiation sensitive field effect transistor
2. Surface charge monitor to indicate the state of the charging environment in the vicinity of the satellite
3. Solar X-ray spectrometer to study the solar flare emission in 4 kev_10 mev energy range using state of the art semiconductor devices.
4. Phoswich scintillation detector and coherent radio beacon experiment to investigate the spatial structure, dynamic and temporal variations of ionosphere and several aspects of equatorial electrodynamics

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Courtesy: ISRO