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GSAT-8: India's powerful indigenous communications satellite

Friday, May 20, 2011

/ Published by Simon L Infimate

Over 500 scientists and engineers worked for almost four years to build the satelite; costs Rs. 675 crore

[caption id="attachment_2263" align="aligncenter" width="580" caption="ISRO GSAT-8 at the ISRO Satellite Integration and Test Establishment in Bangalore. "][/caption]

India's powerful indigenous communications satellite GSAT-8 will be put in orbit by an Ariane 5 launcher on Friday. It will vastly augment television broadcasting, especially Direct To Home (DTH) services, radio networking and other satellite-based services.

The launcher is scheduled to blast off at 17.38 hours local time (0208 a.m.-IST) from here.

GSAT-8, weighing nearly 3,100 kg with 24 transponders in the Ku band, (the portion of the electromagnetic spectrum in the microwave range of frequencies) could not be launched from India because the country's Geosynchronous Satellite Launch Vehicle (GSLV) Mark III, capable of carrying payloads of over 2,000 kg satellites, is still under development.

The lift-off and placing in orbit of the satellite will last 46 minutes – from zero hour when the cryogenic main stage engine is ignited to the final moment when the launcher's main stage falls back off the coast of Africa into the Atlantic Ocean, the ignition of the upper cryogenic stage and the separation of the satellite.

GSAT-8 will separate from the launcher 31 minutes and 17 seconds into the flight. At the time of lift-off, the Ariane 5 will develop a thrust of 13,000kN (Kilo Newton per square metre) or the equivalent of the combined thrust of four Airbus 380 superjumbo jets, in order to break free of the earth's gravitational pull. GSAT-8 will first reach a perigee of 249 km over the equator and be placed in a geostationary orbit at an altitude of 35,947 km with an inclination of 2.5 degrees.

Ariane 5 will also carry ST-2, also a communications satellite that is jointly owned by the Singapore Telecommunications and the Taiwanese Chunghwa Telecom Company. The total payload will be 9,013 kg, including the weight of the two satellites amounting to 8,190 kg.

“It's a complex process that gives all the scientists and engineers involved in the mission a knot in the stomach until the launch is successfully completed and the satellites are safely placed in orbit,” Jacques Denavaut, Arianespace Vice President for Corporate Communications, told The Hindu.

The countdown includes all final preparatory steps for the launcher itself, the satellites as well as the launch site. If all goes according to plan the first step is the ignition of the main stage engine, then the two booster rockets latched to the sides of the main launch vehicle.

The countdown culminates in a synchronised sequence beginning at seven minutes (T-7) before zero hour (T-0). If an interruption in the countdown edges T-0 outside the launch window, then the mission can be postponed by one or more days depending on the problem and its solution. The control station and onboard computers manage the highly complex operation of the countdown. The mission can also be delayed if there are high velocity winds or the possibility of a thunderstorm.

The start of the final countdown begins at T-11 hours and consists of a series of checks as well as operations like the filling of the main cryogenic stage engine with liquid oxygen and hydrogen. At T- 4 minutes, the tanks are pressurised for flight. The “all systems go” report given at T-7 seconds allows the start of the synchronised process. At T-05.5 seconds the cryogenic arms that hold the launcher upright are opened.

At T-4 seconds, the onboard systems take over and at T-3 seconds the guidance systems to flight mode are unlocked.

At 7.05 seconds after the ignition of the main stage cryogenic engine at T-0, the two solid-propellant boosters are ignited enabling lift-off. With a mighty roar and a long orange-red tail flame, the launcher climbs vertically for six seconds then rotates towards the east. The fairing protecting the two satellites is jettisoned shortly after the boosters are jettisoned at an altitude of about 200 km.

At the orbital stage, when the satellites are released, the launcher will attain a velocity of approximately 9,350 metres a second and will be at an altitude of 658 km. The entire process will take 189 seconds from T-0.

Designed, assembled and integrated by the Indian Space Research Organisation (ISRO), GSAT-8 has a design life exceeding 12 years. Other than television and radio networking it will vastly increase the country's capability in fields such as tele-medicine, tele-education, High Definition television (HDTV), the Internet, Research and Rescue, Disaster Management, etc. It will cover the entire country, including the Andaman and Nicobar islands. The satellite also has a two channel GPS Aided Geo Augmented Navigation or GAGAN payload.

“Over 500 scientists and engineers worked for almost four years to build this satellite. Our partners on this project other than the ISRO's own centres, include the Hindustan Aeronautics (HAL), Avasarala Technologies, Larsen and Toubro, SAMEER, the Bharat Heavy Electricals Limited (BHEL) and the National Aerospace Laboratory. The satellite costs Rs. 675 crore, including the launch services,” scientist T.K. Alex, Director of the ISRO Satellite Centre, told The Hindu.

At present, India has seven communications satellites — from INSAT-2E to INSAT-4CR, which provide 151 transponders in S, C, Ext-C and Ku bands.

This will be India's 14th satellite launch from Kourou and Ariane 5's 58th mission, its third launch this year.

~The Hindu

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