GSAT-31 launch from French Guiana: 10 things to know about ISRO's 2.5 Ton satellite

New Delhi, Feb 06: Indian Space Research Organisation (ISRO)'s massive 2,535 kg satellite, GSAT-31, was launch onboard Ariane-5 launch vehicle (VA 247) from French Guiana in the wee hours of Wednesday (IST). The Ariane-5 vehicle injected GSAT-31 into the orbit in a flawless flight lasting about 42 minutes.

GSAT-31 separated from the Ariane-5 in an elliptical Geosynchronous Transfer Orbit with a perigee (nearest point to Earth) of 250 km and an apogee (farthest point to Earth) of 35,850 km, inclined at an angle of 3.0 degree to the equator, ISRO said in a release after the launch.

Ariane 5 is a European heavy-lift launch vehicle that carry payloads weighing more than 10 metric tons to geostationary transfer orbit (GTO) with a high degree of accuracy.

Now the question arises, why the ISRO has chose to go for GSAT-31's launch from French Guiana onboard Ariane-5 when India has its own launchpads in Shriharikota. Firstly, Ariane-5 launch vehicle has a good track record of launching heavy satellites into geostationary transfer orbits with great precision. Ariane-5 can carry payloads weighing more than 10 metric tons to geostationary transfer orbit (GTO) and over 20 metric tons into low-Earth orbit (LEO).

ISRO also has heavy duty launch vehicle- the GSLV series. The payload capacity of the GSLV Mk-2 is about 2 metric tonnes to GTO which will not be able to insert this satellite into orbit. GSLV Mk-3 has payload capacity of 4 metric tonne to GTO. GSLV-Mk III, which is three-stage vehicle with two solid motor strap-ons, a liquid propellant core stage and a cryogenic stage, can technically launch GSAT-31 into GTO.

The probable reason could be this. Launch contracts are often done a couple of years ahead of the launch for such large satellites. Since GSLV Mark III was then technically still in developmental phase, ISRO might have taken a decision to go with Ariane-5, in case GSLV Mk III development gets delayed. GSLV Mk III is designed to carry 4 ton class of satellites into Geosynchronous Transfer Orbit (GTO) or about 10 tons to Low Earth Orbit (LEO), which is about twice the capability of GSLV Mk II.

GSLV MkIII-D2, the second developmental flight of GSLV MkIII, successfully launched GSAT-29, a high throughput communication satellite on November 14, 2018 from Satish Dhawan Space Centre SHAR, Sriharikota. GSAT-29 satellite weighed 3423 kg, far heavier than GSAT-31.

10 things to know about GSAT-31 launch:

• GSAT-31 is the 40th communication satellite of India. The satellite derives its heritage from ISRO's earlier INSAT/GSAT satellite series.

• GSAT-31 will be used for supporting VSAT networks, television uplinks, digital satellite news gathering, DTH television services, cellular back haul connectivity and many such applications.

• GSAT-31 is configured on ISRO's enhanced I-2K Bus, utilising the maximum bus capabilities of this type.

• GSAT-31, with a mission life of 15 years, will augment the Ku-band transponder capacity in Geostationary Orbit.

• The satellite will also provide wide beam coverage to facilitate communication over large oceanic region comprising large part of the Arabian Sea, the Bay of Bengal and the Indian Ocean using wide band transponder.

• Arianespace will orbit two telecommunications satellites using an Ariane 5 from the Guiana Space Center - Saudi Geostationary Satellite 1/Hellas Sat 4, a condosat for KACST (and Hellas Sat; along with GSAT-31 for the ISRO.

• This launch is Ariane 5's 103rd mission and the 70th with an Ariane 5 ECA version.

• Since the launch of India's APPLE experimental satellite on Ariane Flight L03 in 1981, Arianespace has orbited 22 satellites and signed 24 launch contracts with the ISRO.

• Arianespace has signed contracts for Ariane 5 ECA launches up till 2022, after planned introduction of Ariane 6 in 2020.

• Arianespace also won 89% of the geostationary orbit launch contracts opened to non-Indian launch vehicles.