ISRO Gears Up for Next Mk III Launch

The launch will mark ISRO's fifth launch of the year and the second orbital test flight of the GSLV Mk III rocket.

At 5:08 pm today, India will continue its latest chapter in its spaceflight programme with the launch of the GSLV Mk III rocket carrying the GSAT-29 communication satellite from the Satish Dhawan Space Centre, Sriharikota.

The launch of the communication satellite will mark the Indian Space Research Organisation’s (ISRO’s) fifth launch of the year and will be the second test flight of the Mk III rocket, ISRO’s heaviest. The vehicle is capable of lifting four-tonne satellites into the geostationary transfer orbit (GTO).

The GSAT-29 communications satellite carries high throughput communication transponders in the Ka and Ku bands. They will expand high-speed data transfer in remote areas, including over difficult terrain, including in the Northeast and Jammu and Kashmir. The satellite has a planned operational life of over 10 years.

Also read: After GSLV Mk III Cruises to Success, ISRO Is Back to Its Hectic Schedule

The launch was originally slated for 5:08 am but was subsequently postponed by 12 hours to avoid being disrupted by Cyclone Gaja. Gaja was previously expected to make landfall between Chennai and Sriharikota, but it has since changed course. The 27-hour countdown began at 2:50 pm on Tuesday.

K. Sivan, the chairman of ISRO, said the Wednesday launch was among the “very important missions and a milestone” for India’s space programme. If the mission is a success, the GSLV class of rockets will be declared operational and join the PSLV.

However, the GSLV is far from establishing the same reliability as the PSLV rockets have. More successful launches over a larger time frame will be necessary to achieve that.

In the meantime, ISRO is also building a rocket to launch small satellites and capitalise on the booming small-sats market. The unsurprisingly named SSLV – ‘small satellite launch vehicle’ – is expected to be ready by the decade’s close.

On the other hand, the GSLV is a behemoth reserved for large satellites. And the Mk III, although only 43.5 metres tall, has a liftoff mass of 641 tonnes and is ISRO’s most muscular launch vehicle to date. The PSLV itself stands 44 metres.

It has twice the payload capacity as the Mk II version. But for the similar names, the Mk II and Mk III are of different design and use different kinds of cryogenic engines for their respective upper stages.

The Mk III “is powered by two S200 solid motors, one L110 liquid core stage and a powerful liquid cryogenic stage, C25,” Sivan said. The Mk II uses the CE 7.5 engine. The basic principle of all cryogenic engines is that they generate higher thrust by using liquid hydrogen as fuel.

Following liftoff, the rocket’s uppermost stage is expected to inject the satellite into the highly elliptical transfer orbit, at an altitude of 35,975 km. From there, the satellite will use its inbuilt propulsion system to move itself to the geostationary orbit, at 36,000 km.

Also read: GSLV Gyan: Why Experts Think the Mk III Is a Big Deal for ISRO and India

As The Wire has previously reported, eight ISRO satellites launched onboard Ariane rockets between 2005 and 2016 cost the organisation almost Rs 4,200 crore. Rockets like the Mk II and Mk III are expected to help reduce these expenditures.

A successful launch will also pave the way for producing more advanced satellites, Sivan said. “This vehicle is going to launch the Chandrayaan-II and also the manned mission. We are getting prepared for that.”

In 2014, the first successful flight of GSLV Mk III went off without a hitch when it carried a crew module as its payload. The second flight lifted GSAT-19 to orbit on June 5, 2017.

Success will also provide ISRO with some much needed encouragement: the organisation lost access to the GSAT-6A satellite in March after only a day in space and the GSAT-11 satellite had to be recalled from its launch in French Guyana to fix some issues that had been overlooked during testing.

(With inputs from PTI)