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GSAT-8 to vastly augment DTH services, radio networking

Vaiju Naravane
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Over 500 scientists, engineers worked for almost four years to build the satellite; costs Rs. 675 crore

GSAT-8 at the ISRO Satellite Integration and Test Establishment in Bangalore. —Photo: courtesy ISRO
GSAT-8 at the ISRO Satellite Integration and Test Establishment in Bangalore. —Photo: courtesy ISRO

GSAT-8, a powerful, indigenously produced communications satellite, designed to vastly augment television broadcasting, especially Direct To Home (DTH) services, radio networking and other satellite-based services in India, is scheduled to blast off at 17.38 local time (2.08 am IST) on board an Ariane 5 launcher from the French Space Centre in Kourou, French Guiana on Friday.

The GSAT-8, an extremely powerful satellite weighing nearly 3100 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 2000 kg class satellites is still under development.

The lift off and placing into 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 rocket 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. The launch window opens at 17.38 local time and closes at 18.10 local time. If the launch cannot take place during that period the mission can be delayed.

The 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 4 Airbus 380 superjumbo jets, in order to break free of the earth's gravitational pull.

The GSAT-8 will first reach a perigee altitude 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.

Besides India's GSAT-8 the launcher will carry ST-2,, another communications satellite jointly owned by Singapore Telecommunications and the Taiwanese Chunghwa Telecom Company on this mission. The total payload will be 9013 kg, including the weight of the two satellites amounting to 8190 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 safely placed into orbit,” Jacques Denavaut, the Arianespace Vice President for Corporate Communications toldThe 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 on-board computers manage the highly complex operation of the countdown. The mission can also be delayed if there are high velocity northerly 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 kept at a temperature of minus 250 degrees Celcius.

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 synchronized 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 containing 250 tonnes of dry powder 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 nose fairing protecting the two satellites is jettisoned shortly after the boosters are jettisoned at an altitude of about 200 kilometres.

At the orbital stage, when the satellites are released, the launcher will have attained a velocity of approximately 9350 metres per second and will be at an altitude of 658 km. The entire process will have taken 189 seconds from T-0.

Designed, assembled and integrated by the Indian Space Research Organisation (ISRO), the 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 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,” Padmashree and distinguished scientist T.K. Alex, the Director of the ISRO Satellite Centre toldThe Hindu.

Currently 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 fifty-eighth mission, its third launch this year.


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