For the GSLV programme, reliability and lifting heavier satellites remain key challenges

Not only did the use up of spare satellites leave India with no reserve available for contingencies, but the entire space segment was left idle because of the delays in building the ground and user segments

India’s Geosynchronous Satellite Launch Vehicle (GSLV Mk II) has successfully launched a navigation satellite NVS-01/IRNSS-1J. This is the first of the second generation satellites being launched for augmenting the Indian Regional Navigation Satellite System/Navigation with Indian Constellation (IRNSS/NavIC).

Through this mission, the Indian Space Research Organisation (ISRO) is trying to rectify the serious issues faced with the atomic clocks used before on the NavIC satellites that were standing up the GSLV Mk II as a successful launcher.

Imports That Failed

The NavIC project was approved in 2006 for providing positioning, navigation and timing (PNT) services for civilian (Standard Positioning Service), defence and strategic users (Restricted Service). The primary service area is India’s mainland and the region extending 1,500 kms from the country’s boundaries.

The first generation satellites (IRNSS-1A to IRNSS-1I) under this project were launched between 2013 and 2018. This first generation was planned to operate with seven satellites while two were reserved as spare. However, all the atomic clocks onboard the IRNSS-1A failed, forcing ISRO to launch a spare. These clocks were imported from Switzerland, with the defective clocks also affecting Europe’s Galileo PNT system. The atomic clocks are the heart of the PNT architecture.

The replacement satellite, IRNSS-1H failed to deploy as the payload fairing of the Polar Satellite Launch Vehicle (PSLV) did not separate after the launch. This trapped the satellite inside the fairing. Subsequently, the second replacement satellite (IRNSS-1I) was launched and placed into orbit successfully. The IRNSS-1A is currently being used for messaging services sending weather alerts etc.

Not only did the use up of spare satellites leave India with no reserve available for contingencies, but the entire space segment was left idle because of the delays in building the ground and user segments. India’s Comptroller and Auditor General calculated in 2018 that the satellites were lying idle between 14 months to four years, depending on their launch schedule, because of this delay.

The second generation satellites are expected to enhance the PNT service by transmitting the civilian signals in the L1 band in addition to the signals being transmitted already in the L5 and S bands. India is also using the indigenously developed Rubidium atomic clocks in the new generation of satellites, which will be put to test in space for resiliency and accuracy.

The GSLV Saga

The second generation satellites are also heavier, weighing about 2,232 kg at launch, compared to the first generation that weighed about 1,425 kg at lift-off. This necessitated the use of the geosynchronous launch vehicles, with the GSLV Mk II capable of launching 2,250 kg to a geosynchronous transfer orbit.

Like the atomic clocks, the use of this launch vehicle also came with great risk. The GSLV Mk II does not hold a launch success rate that is comparable to the PSLV or what the GSLV MK III (now known as LVM3) is trying to achieve. The use of Russian cryogenic engines and the launcher being used as a test vehicle for an indigenously developed cryogenic upper stage (CUS) did not bode well for its success rate.

The Russian engines were used in six of the seven launches that happened between 2001 and 2010. The  first two developmental flights and the first operational flight were successful, but two of them, launched in 2006 (GSLV-F02) and December 2010 (GSLV-F06), were destroyed by the range safety officer as they veered off the trajectory. Another developmental flight (GSLV-D3) launched in April 2010 also failed as the cryogenic upper stage (CUS) used for the first time failed to sustain the combustion.

After a hiatus of four years, the GSLV Mk II (GSLV-D5) was relaunched successfully using the indigenous CUS in 2014. The launcher attained operational status in 2016 following another developmental flight in 2015. It had a successful streak of four operational flights before the CUS failed again in 2021.

Retire GSLV Mk II

This underperformance and the lower launch cadence made the GSLV Mk II less reliable over its peers. The increasing satellite weight over the past years could not be met even by the GSLV Mk III, though it is capable of launching 4,000 kg to a geosynchronous transfer orbit (therefore requiring ISRO to depend on Arianespace to launch the 4,180 kg GSAT-24 communication satellite). Therefore, it makes sense to retire the production line of the GSLV Mk II and reallocate the resources for improving the performance of GSLV Mk III and manufacturing heavier versions of the CUS. The commercial success of the GSLV Mk III will also weigh against continuing the operation of the GSLV Mk II.

In fact, media reports indicate ISRO may already be considering executing this option after a few more flights of GSLV Mk II. These flights would most probably include the launch of the rest of the four peer satellites of NVS-01.

With the space segment of NavIC gaining strength, the Indian government should encourage the development of user modules and allied applications for fast adoption of this system in the country and in the neighbourhood.

Vidya Sagar Reddy is a research analyst on outer space affairs. He tracks Indian, Chinese and American space activities. Vidya has published book chapters, and research articles in the Astropolitics and NewSpace journals. He also provided analyses for The Space Review, SpaceNews, East Asia Forum and DNA India. Views are personal, and do not represent the stand of this publication.