Spaceflight Insider

India to launch GSAT-6 communication satellite Thursday

GSLV-D6 being moved from the Vehicle Assembly Building to the Launch Pad at the Satish Dhawan Space Centre in Sriharikota

GSLV-D6 being moved from the Vehicle Assembly Building to the Launch Pad at the Satish Dhawan Space Centre in Sriharikota. Photo Credit: ISRO

The Indian Space Research Organisation (ISRO) is slated to deliver the country’s GSAT-6 (also known as INSAT-4E) communications satellite to orbit on Thursday, Aug. 27. It will employ the heavy-lift version of its Geosynchronous Satellite Launch Vehicle (GSLV).

The mission, designated GSLV-D6, is scheduled to take to the skies at 4:52 p.m. local time (7:22 a.m. EDT) from the Second Launch Pad at the Satish Dhawan Space Centre SHAR (SDSC SHAR) located in Sriharikota.

The Mission Readiness Review (MRR) committee and the Launch Authorisation Board (LAB) have already cleared the booster for Thursday’s planned lift-off. The 29-hour countdown for the launch will start on Wednesday, Aug. 26, at 11:52 a.m. local time (2:22 a.m. EDT).

If everything goes as planned, India’s powerful GSLV booster will send the GSAT-6 satellite into a Geosynchronous Transfer Orbit (GTO). After reaching the designated orbit, the satellite will use its own propulsion system to reach its final geostationary orbital “home” and will be stationed 83 degrees East longitude.

The cuboid-shaped GSAT-6, weighing 2.1 metric tons, is an advanced multimedia communication satellite. It will offer a Satellite Digital Multimedia Broadcasting (S-DMB) service across several digital multimedia terminals or consoles that can be used to provide information services to vehicles on the fly and to mobile phones.

The spacecraft will also provide a platform for developing techniques and technologies which could be useful in future satellite-based mobile communications applications. These include demonstrating the use of large, unfurlable antenna on spacecraft, handheld ground terminals, and network management techniques.

The satellite will have five C × S transponders, each with a 9 MHz bandwidth, and five S × C transponders, each with 2.7 MHz bandwidth. It is anticipated that together they will cover the entire country. One of the advanced hardware of the GSAT-6 satellite is its 20 ft (6 m) long S-Band Antenna, the largest antenna ever built by ISRO. The satellite is planned to be operational for nine years.

“One of the advanced features of [the] GSAT-6 satellite is its S-Band unfurlable antenna. This is the largest satellite antenna realized by our space agency. The antenna will be utilized for five spot beams over the Indian [mainland],” ISRO chairman Kiran Kumar told the Hindustan Times.

GSAT-6 seen with two halves of payload faring of the GSLV-D6.

GSAT-6 seen with two halves of payload fairing of the GSLV-D6. (Click to enlarge.) Photo Credit: ISRO

The GSAT satellites are India’s indigenously developed communications satellites, used for digital audio, data, and video broadcasting.

“It will give you a capability with very small hand-held device to communicate, so like a small mobile you can communicate directly through the satellite to any other part, because the antenna size is very large, so it has got a signal grasping power much larger,” Kumar added.

The Indian National Satellite (INSAT) system is one of the largest domestic communication satellite systems in the Asia-Pacific region with nine operational communication satellites placed in Geostationary orbit. Established in 1983 with the commissioning of the INSAT-1B, it initiated a major revolution in India’s communications sector. Currently operational communication satellites include INSAT-3A, INSAT-3C, INSAT-3E, INSAT-4A, INSAT-4B, INSAT-4CR, GSAT-8, GSAT-10, and GSAT-12.

The system currently has a total of 195 transponders in the C, Extended C, and Ku-bands providing services that include telecommunications, television broadcasting, satellite news gathering, societal applications, weather forecasting, disaster warning, and Search and Rescue operations.

For this mission, the GSLV launch vehicle is configured with all of its three stages including the Cryogenic Upper Stage (CUS). This arrangement is similar to the one that was successfully flown during the previous GSLV-D5 mission in January 2014, which had successfully placed the GSAT-14 satellite into GTO.

The metallic payload fairing of the GSLV-D6 has a diameter of 11.1 ft (3.4 m). The overall length of GSLV-D6 is 161 ft (49 m) with a lift-off mass of 416 metric tons.

The CUS stage that will be used on the GSLV-D6 mission is designated as CUS-06. A Cryogenic rocket stage is considered by some to be more efficient and provides more thrust for every ton of propellant it burns compared to solid and Earth-storable liquid propellant rocket stages.

The cryogenic stage is a complex system due to its use of propellants at extremely low temperatures and the associated thermal and structural challenges involved with sending it skyward. Oxygen liquefies at –183 degrees C and hydrogen at –253 degrees C. The propellants, at these low temperatures, are pumped using turbo pumps running at around 40,000 rpm.

The main engine and two smaller steering engines of the CUS together provide a nominal thrust of about 73.55 kN in a vacuum. During the flight, the CUS fires for a nominal duration of approximately 720 seconds.

The GSLV is an expendable launch system developed to enable India to launch its satellites without dependence on foreign launch service providers. It uses major components that have already been proven by the Polar Satellite Launch Vehicle (PSLV) launchers in the form of the S125/S139 solid rocket booster and the liquid-fueled Vikas engine.

For Thursday’s launch, the GSLV Mk II variant will be used. This version of the rocket uses an Indian cryogenic engine – the CE-7.5 – and it is capable of launching 2.5 metric tons into GTO. Previous GSLV vehicles (GSLV Mk I) have used Russian cryogenic engines.

GSLV employs S-band telemetry and C-band transponders for enabling vehicle performance monitoring, tracking, range safety / flight safety, and Preliminary Orbit Determination (POD). The Redundant Strap Down Inertial Navigation System/Inertial Guidance System of the GSLV is housed in its equipment bay and it guides the vehicle from lift-off to spacecraft separation.

The first development flight of the GSLV Mk I (GSLV-D1) took place on April 18, 2001. That flight carried GSAT-1 failed to reach the correct orbit. Attempts to save GSAT-1 by using its own propulsion system to maneuver it into the proper orbit were also unsuccessful as it ran out of fuel several thousand miles below geosynchronous orbit.

GSLV-D6 will be the ninth flight of the GSLV boosster. GSAT-6 is the country’s 25th geostationary communications satellite built by ISRO and the 12th in the GSAT series.


Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski's generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.

Reader Comments

All the Best for GSAT-6 Launch.

⚠ Commenting Rules

Post Comment

Your email address will not be published. Required fields are marked *