GSLV

The Geosynchronous Satellite Launch Vehicle (GSLV) is an advanced launch vehicle developed by the Indian Space Research Organisation (ISRO) to place satellites into geosynchronous and geostationary orbits. It represents a major milestone in India’s space technology, enabling the country to achieve self-reliance in launching heavier communication and weather satellites. Since its inception, the GSLV programme has played a vital role in enhancing India’s satellite launch capabilities and strengthening its presence in global space exploration.

Background and Development

India’s space launch programme began with the development of the Satellite Launch Vehicle (SLV) in the 1980s and the Polar Satellite Launch Vehicle (PSLV) in the 1990s. While the PSLV proved reliable for placing satellites into polar orbits and sun-synchronous orbits, India lacked the capability to launch heavier payloads into geostationary transfer orbits (GTO) — the orbit required for communication and weather satellites.
To overcome this limitation, ISRO initiated the GSLV programme in 1990. Its objective was to develop a three-stage launch vehicle equipped with a powerful cryogenic upper stage, enabling India to place satellites weighing up to 2,500 kilograms into GTO. The GSLV project also aimed to reduce dependence on foreign launch services, particularly for INSAT and GSAT series communication satellites.
The first developmental flight of the GSLV took place on 18 April 2001, marking India’s entry into the class of nations capable of launching satellites into geosynchronous orbit.

Design and Technical Features

The GSLV is a three-stage launch vehicle, each stage designed to perform specific functions during ascent:

1. First Stage (Solid Booster Stage)
   • Powered by a large solid rocket motor (S-139) using hydroxyl-terminated polybutadiene (HTPB) as propellant.
   • Augmented by four liquid strap-on boosters using unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N₂O₄) as fuel and oxidiser.
2. Second Stage (Liquid Stage)
   • Employs the Vikas engine, a reliable liquid-fuelled engine derived from French Viking technology.
   • Provides thrust for mid-flight propulsion and trajectory control.
3. Third Stage (Cryogenic Upper Stage)
   • Uses liquid hydrogen (LH₂) as fuel and liquid oxygen (LOX) as oxidiser.
   • The cryogenic engine operates at extremely low temperatures (below −250°C) and provides high efficiency, enabling the rocket to achieve the velocity needed for GTO insertion.

The total height of the GSLV is approximately 49 metres, and its lift-off mass is around 415 tonnes. The vehicle is launched from the Satish Dhawan Space Centre (SDSC), Sriharikota, on India’s eastern coast.

Variants of GSLV

Over the years, ISRO has developed several variants of the GSLV, each improving upon the previous design:

• GSLV Mk I and Mk II: Early versions that used a mix of Indian and Russian technologies. The Mk I initially employed a Russian cryogenic stage (KVD-1), while the Mk II used the indigenously developed cryogenic upper stage (CUS).
• GSLV Mk III (also known as LVM3): A significantly upgraded and more powerful version capable of launching 4-tonne-class satellites into GTO and up to 10 tonnes into low Earth orbit (LEO). The Mk III is a three-stage vehicle featuring twin S-200 solid strap-on boosters, an L110 liquid core stage, and a C25 cryogenic upper stage.

The GSLV Mk III is considered India’s heavy-lift launch vehicle and has been used for critical missions such as Chandrayaan-2 (2019) and Chandrayaan-3 (2023).

Notable Launches

Some significant milestones in the GSLV programme include:

• GSLV-D1 (2001): First developmental flight; partial success due to orbit deviation.
• GSLV-D2 (2003): Successful launch of GSAT-2 satellite.
• GSLV-F04 (2007): Successful placement of INSAT-4CR in orbit.
• GSLV-D5 (2014): First successful flight with India’s indigenous cryogenic engine (CE-7.5), launching GSAT-14 — a landmark in India’s space technology.
• GSLV-F09 (2017): Launched the South Asia Satellite (GSAT-9), promoting regional cooperation.
• GSLV Mk III-M1 (2017): Launched GSAT-19, demonstrating India’s heavy-lift capability.
• GSLV Mk III-M1 (2019): Carried Chandrayaan-2, India’s second lunar mission.

Indigenous Cryogenic Technology

One of the greatest achievements of the GSLV programme was the development of indigenous cryogenic engine technology. Initially, India procured cryogenic engines from Russia in the 1990s, but restrictions under the Missile Technology Control Regime (MTCR) curtailed further transfers. As a result, ISRO undertook independent development of a cryogenic engine — a complex process involving the management of supercooled propellants and precision engineering.
After two unsuccessful attempts, ISRO achieved success with the GSLV-D5 mission in 2014, which marked the operational validation of the Indian cryogenic engine. This breakthrough established India as one of the few nations with mastery of cryogenic propulsion technology.

Applications and Importance

The GSLV is used primarily for launching:

• Communication satellites (GSAT series).
• Meteorological and remote sensing satellites.
• Interplanetary missions, such as lunar and Mars probes.

Its capability to launch heavier payloads has strategic and economic importance:

• It reduces dependence on foreign launch services such as ArianeSpace.
• It strengthens India’s position in the global commercial satellite launch market.
• It supports India’s space diplomacy by enabling the launch of satellites for friendly nations.

Challenges and Setbacks

The GSLV programme faced numerous technical challenges and initial failures. Early missions were plagued by cryogenic stage malfunctions, guidance issues, and structural instabilities. Each setback, however, led to systematic improvements in design, quality control, and reliability.
By the mid-2010s, the vehicle achieved a high success rate, with reliability exceeding 80%. Continuous testing and refinement have made the GSLV one of the most dependable components of India’s space arsenal.

Future Prospects

ISRO continues to upgrade the GSLV family for greater payload capacity and mission flexibility.

• The GSLV Mk III (LVM3) has been chosen as the launch vehicle for Gaganyaan, India’s first crewed space mission.
• Future enhancements include the development of semi-cryogenic engines (SC120) to improve efficiency and thrust.
• The GSLV series will continue to play a central role in India’s plans for deep-space exploration, satellite navigation, and global communication services.