Indian GSLV launches with GSAT-6

by William Graham

India’s Geosynchronous Satellite Launch Vehicle has successfully deployed a communications satellite Thursday, with the rocket’s ninth flight lofting the GSAT-6 spacecraft. The launch was on schedule at 16:52 local time (11:22 UTC) with the launch taking place from the Satish Dhawan Space Centre on Sriharikota Island.

ISRO Launch:

The ninth flight for the Geosynchronous Satellite Launch Vehicle (GSLV) across its Mark I and II variants, Thursday’s launch was conducted by the Indian Space Research Organisation (ISRO).

First flown in April 2001, the GSLV has had something of a troubled history; of its eight launches to date, three completed their missions successfully, one reached a lower-than-planned orbit which was corrected at the expense of several years’ operational life for its payload, one reached an unusable low orbit that could not be corrected and three failed to achieve orbit altogether.

Following the success of the previous launch – which carried the GSAT-14 spacecraft to orbit in January 2014 – ISRO was hoping for the GSLV’s first back-to-back successes since the type’s second and third flights in 2003 and 2004 respectively. That proved to be the case.

The GSLV’s Mark I and II configurations differ in that the Mark I uses a third stage powered by a Russian-built engine, while the Mark II introduces a replacement using Indian components.

A third rocket, the GSLV Mark III, made its maiden flight last December. However, this is essentially a new rocket sharing little more than a name with its predecessors.

2015-08-27-091812The payload of Thursday’s launch, GSAT-6, is a 2,117-kilogram (4,667 lb) communications satellite constructed by ISRO around the I-2K satellite bus.

Designed for nine to twelve years of service, the satellite carries an 80-centimetre (2.6 ft) C-band antenna for providing a single fixed beam and a six metre (16-foot) deployable antenna that will facilitate five S-band spot beams. Electrical power comes from a pair of solar arrays generating 3.1 kilowatts for the spacecraft’s systems.

Following launch the spacecraft will make use of a liquid bipropellant apogee motor, fuelled by monomethylhydrazine and mixed oxides of nitrogen, to achieve geostationary orbit where it will be operated at a longitude of 83 degrees east. According to reports the satellite will most likely be used to relay military communications.

2015-08-27-092034Ahead of the launch, which took place from the Second Launch Pad at the Satish Dhawan Space Centre, assembly of the rocket and payload integration took place vertically away from the launch pad in the centre’s vehicle assembly building. The rocket was moved to the launch pad atop a mobile platform on Saturday 22 August.

Thursday’s launch was the fifteenth from the Second Pad – one of two complexes that India’s GSLV and PSLV rockets can fly from along with the nearby First Launch Pad.

Since the completion of the second pad in 2005, the GSLV has flown only from the newer pad with the PSLV launching from whichever is available for it. Past launches from the second pad have included nine PSLVs, five GSLVs, and a single suborbital launch of the GSLV Mark III last December.

2014-12-18 01_02_17-ISRO GSLV - Google SearchThe GSLV that deployed GSAT-6 was a Mark II vehicle, featuring India’s indigenous cryogenic upper stage in place of the Russian-engined version used on the Mark I.

Thursday’s launch was the third flight of the Mark II GSLV, whose maiden flight was the unsuccessful attempt to orbit GSAT-4 in 2010, but which has achieved success with the more recent launch of GSAT-14 in 2014. The serial number of the rocket which will be used for the GSAT-6 mission is GSLV-D6.

The first stage of the GSLV consists of four L40-H strap-on liquid rocket motors clustered around a solid-fuel core stage powered by an S139 motor.

2015-08-27-092340Each powered by a Vikas liquid rocket motor burning 42.6 tonnes (41.9 Imperial tons, 47.0 US tons) of fuel, the strap-ons make use of a mixture of unsymmetrical dimethylhydrazine and hydrazine hydrate, in a ratio of three parts to one, oxidised by dinitrogen tetroxide.

The four strap-on motors ignited around 4.8 seconds in advance of liftoff, with the solid-fuelled core igniting once the countdown reached zero.

The first stage core burned for one minute and forty-six seconds before depleting its hydroxyl-terminated polybutadiene (HTPB) fuel. After this, thrust continued to be generated by the four strap-on motors until their shutdown two minutes and 29 seconds into the mission.

2015-08-27-092454Half a second after cutoff, the second stage separated from the spent first. Ignition of the second stage’s Vikas engine occurred about another half a second after staging.

Separation of the payload fairing from the nose of the rocket occurred three minutes and fifty seconds after launch, with the rocket at an altitude of approximately 115.45 kilometres.

The GSLV’s second stage completed its two-minute, 40-second burn at the four minute and forty-nine second mark in the mission. Separating four seconds after cutoff, the spent stage made way for the third stage to begin its burn.

Powered by a single cryogenic engine fuelled by liquid hydrogen and liquid oxygen, the third stage fired for two seconds short of twelve minutes to raise GSAT-6 into its targeted deployment orbit.

2015-08-27-092526Spacecraft separation occurred twelve seconds after the end of the GSLV’s powered flight, at 17 minutes and four seconds mission elapsed time.

Thursday’s launch was aiming for a geosynchronous transfer orbit with a perigee of 170 kilometres (106 miles, 91.8 nautical miles) an apogee of 35,975 kilometres (22354 miles, 19425 nautical miles) and 19.95 degrees inclination.

India’s third orbital launch of 2015 – following PSLV missions in March and July – Thursday’s launch was the first and only planned GSLV launch of 2015.

The rocket is next expected to fly in 2016 carrying the GSAT-9 spacecraft. Before then ISRO will launch several Polar Satellite Launch Vehicles, with the smaller rocket’s next launch currently slated to carry the AstroSat-1 astronomy spacecraft and several smaller payloads at the end of September.

The GSAT-6 launch was the forty-second launch that will attempt to achieve orbit this year – a number which includes the Proton-M and Falcon 9 launches in May and June that failed to achieve orbit, the April Soyuz-2-1a failure with Progress M-27M which nonetheless reached orbit, and the February Vega launch which briefly attained orbit following a successful suborbital primary mission.

(Images via ISRO)

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