Countdown begins for launch of Indian military satellite

India's Geosynchronous Satellite Launch Vehicle rolls out to the Second Launch Pad at its launch base on Sriharikota Island on India's east coast.
India’s Geosynchronous Satellite Launch Vehicle rolls out to the Second Launch Pad at its launch base on Sriharikota Island on India’s east coast.

A government-owned communications satellite heading for geostationary orbit 22,300 miles above Earth is set for launch Thursday to on a nine-year mission to to support the Indian military.

The 4,667-pound GSAT 6 spacecraft will lift off aboard India’s Geosynchronous Satellite Launch Vehicle at 1122 GMT (7:22 a.m. EDT) Thursday from the Satish Dhawan Space Center, a spaceport situated about 50 miles north of Chennai on India’s east coast.

Shrouded inside the GSLV’s metallic nose fairing, the satellite is India’s 25th geostationary communications satellite and has a mission to serve “strategic users,” according to the Indian Space Research Organization. Indian news reports said the prime customer for the new signal relay craft is the Indian military.

ISRO officials said the 29-hour countdown began Wednesday, and launch crews planned to fill the rocket’s four liquid-fueled boosters and second stage with storable¬†hydrazine and nitrogen tetroxide propellants later in the day. Fueling of the GSLV’s third stage with cryogenic liquid hydrogen and liquid oxygen will come in the final hours of the countdown.

The first stage’s solid propellant load was packed inside the motor when it was assembled.

Launch is scheduled for 4:52 p.m. local time Thursday at the Indian launch base, and 161-foot-tall GSLV will fire away on the power of four hydrazine-burning strap-on Vikas booster engines and a solid-fueled core motor. At peak power, the first stage and the boosters will generate more than 1.7 million pounds of thrust.

The four liquid-fueled boosters will ignite at T-minus 4.8 seconds and ramp up to full thrust before the solid first stage fires when the countdown clock reaches zero.

The core motor will consume its propellant load by T+plus 1 minute, 46 seconds, followed by shutdown of the four Vikas booster engines at T+plus 2 minutes, 29 seconds. A single second stage Vikas powerplant will take over and burn until just shy of the mission’s five-minute point, during which time the GSLV’s payload fairing will release once the rocket is out of the dense lower atmosphere — a milestone projected at T+plus 3 minutes, 50 seconds.

A cryogenic upper stage engine will ignite at T+plus 4 minutes, 54 seconds, for a nearly 12-minute firing to propel the GSAT 6 satellite into an oval-shaped geostationary transfer orbit. Spacecraft separation is schedule for T+plus 17 minutes, 4 seconds, according to ISRO.

The launch is targeting an orbit with a high point of 22,353 miles (35,975 kilometers), a low point of 105 miles (170 kilometers) and an inclination of 19.95 degrees.

Thursday’s launch marks the third time the Indian-built cryogenic engine, which burns a super-cold mixture of liquid hydrogen and liquid oxygen, has flown on the GSLV. Earlier GSLV flights, dating back to the rocket’s maiden mission in 2001, employed a Russian-made cryogenic third stage.

India's GSAT 6 communications satellite is pictured before encapsulation inside the GSLV's payload fairing. Credit: ISRO
India’s GSAT 6 communications satellite is pictured before encapsulation inside the GSLV’s payload fairing. Credit: ISRO

The all-Indian version of the GSLV, called the GSLV Mk.2, failed on its first launch in April 2010 due to a failure in the upper stage engine’s liquid hydrogen turbopump. The second test launch of the GSLV Mk.2 in January 2014 was successful.

The launch of GSAT 6 is the ninth flight of the GSLV in both its all-Indian and part-Russian configurations. ISRO considers four of the eight launches to date as successful.

Thursday’s launch, designated GSLV-D6 by ISRO, is India’s third space mission of the year after two flawless flights of the smaller Polar Satellite Launch Vehicle.

GSAT 6 will fire its on-board propulsion system to circularize its orbit 22,300 miles above the equator, where it will park itself at 83 degrees east longitude and unfurl a nearly 20-foot (6-meter) S-band antenna, the largest reflector of its kind ever flown on an Indian communications satellite.

The spacecraft carries S-band and C-band communications payloads with five spot beams and one nationwide beam.

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