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Why ISRO’s latest launch carries weight

At 2,250 kg, GSAT-7A is the heaviest satellite launched by GSLV-Mk-II since it began using the indigenous cryogenic engine after carrying out early development flights with Russian cryogenic engines.

Written by Johnson T A | Bengaluru |
Updated: December 20, 2018 6:50:46 am
isro gsat 7a, isro gsat 7a launch, isro gsat 7a launch live, isro gslv f11, isro gslv f11 launch, isro gsat 7a satellite, isro gsat 7a satellite launch video, Indian express Weighing 2,250kg, the GSAT-7A satellite is expected to bolster the communication systems of the Indian Air Force. (Source: ISRO)

Given its recent track record in launching satellites on its fourth-generation rockets, Geosynchronous Satellite Launch Vehicles (GSLV), the Indian Space Research Organisation (ISRO) was continuing a trend Wednesday when GSLV-F11 launched a communication satellite, GSAT-7A.

Heavier and heavier

The standout factor with Wednesday’s launch and 12 other successful flights carried out so far by ISRO’s GSLV-Mk-II rocket —including six successive flights since 2014 with an indigenous cryogenic fuel upper stage — is that the rocket was pushing the limits of its capabilities in launching satellites of the two-tonne class for the seventh time. At 2,250 kg, GSAT-7A is the heaviest satellite launched by GSLV-Mk-II since it began using the indigenous cryogenic engine after carrying out early development flights with Russian cryogenic engines. “The cryogenic stage of this vehicle has been modified to increase the thrust rate,’’ ISRO chairman K Sivan said after the copybook launch.

GSAT-7A is an advanced communication satellite with a Gregorian Antenna and other new technologies, the ISRO chairman said. The satellite operating in the Ku band will service communication needs for network-centric operations of the IAF and the military.

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“GSAT-7A is the 39th Indian communication satellite of ISRO to provide services to users in Ku-band over the Indian region. Most of the functional requirements of the communication payloads and the other systems have been derived from ISRO’s earlier geostationary INSAT/GSAT satellites,” ISRO said. GSAT-7A was built on a standard 2,000-kg satellite bus used over the years by ISRO.

GSLV-F11 lifted off at 04:10 pm and about 19 minutes later, “injected GSAT-7A into a Geosynchronous Transfer Orbit (GTO) of 170.8 km × 39127 km — very close to the intended orbit”, ISRO said.

The GSLV programme

GSLV-Mk-II is ISRO’s fourth generation rocket with three stages. The first stage has four liquid strap-ons and a solid rocket motor, the second has a high thrust engine using liquid fuel, the third is the cryogenic upper stage. The indigenous cryogenic engine was tested successfully for the first time on January 5, 2014; a launch had failed on April 15, 2010. The cryogenic stage uses liquid hydrogen as fuel and liquid oxygen as an oxidiser. Compared to solid and earth-storable liquid propellant stages, it is a highly efficient rocket stage that provides more thrust for every kg of propellant it burns.

ISRO initially used seven cryogenic engines sold by Russia for the early phase of its GSLV programme that began in 2001. GSLV launches with Russian engines have had mixed success, with only two flights performing well.


ISRO is developing a more powerful, fifth-generation GSLV-Mk-III rocket to launch satellites in the 4-6-tonne category. GSLV-Mk-III had a successful development flight last month when it launched the 3,423-kg GSAT-29 communication satellite. GSLV-Mk-III is the designated launch vehicle for India’s second moon mission next year and the first human space flight scheduled for 2022.

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First published on: 20-12-2018 at 02:30:50 am
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