The GSLV Saga

Geosynchronous Satellite Launch Vehicle (GSLV) is designed to launch 2.0 ton class of satellites into Geosynchronous Transfer Orbit (GTO).  The three stage GSLV adopts the flight-proven solid and liquid stages of ISRO’s Polar Satellite Launch Vehicle (PSLV) and a cryogenic upper stage. The first stage comprises a solid propellant core motor and four liquid propellant strap-ons.  The second stage is powered by a single liquid propellant engine.  The third stage is a Cryogenic Stage with 12 tons of propellant loading. The launch vehicle stands 49 meters tall and weighs 416 tons at lift-off with a core diameter of 2.8 meters.
The GSLV has basically evolved from the rugged flight-proven PSLV.  The solid propellant core motor of GSLV, called S139, is derived from the PS1 core stage of PSLV.  Four liquid-fueled strap-ons, called L40, are clustered around the core stage.  The second stage of the GSLV, designated as GS2, and the four L40 stages, use earth-storable liquid propellants and are derivatives of the PSLV’s second stage.  The third stage of GSLV is the cryogenic stage, which uses liquid Hydrogen as fuel and liquid Oxygen as oxidiser. Liquid Oxygen is stored at -183 °C while liquid Hydrogen is stored at -253 °C in two separate tanks.
The major subsystems of cryogenic engine are the combustion chamber, gas generator, turbo pump, start up system, etc.  In spite of the complexity and challenges, these fluids are preferred due to their ability to produce maximum thrust for every kilogram of propellant and the cryogenic engines are the most efficient engines in use for launch vehicles. Since ISRO did not have the Cryogenic technology, the initial launches of GSLV were flown with procured Russian Cryo Stage. At the same time, efforts were on to develop our own Cryo engine and Stage.
The current version of GSLV has a payload Fairing of 3.4 metre diameter made of Aluminium Alloy. This Fairing houses the satellite during the launch phase through the atmospheric regime.
The vehicle is equipped with an Inertial Navigation and Guidance System for computing the inertial position and guiding the vehicle from lift-off to satellite injection. The Digital Auto Pilot and the Closed Loop Guidance scheme ensure the required attitude (orientation) manoeuvres and guided injection of the satellite.
GSLV had its maiden launch on April 18, 2001. Subsequently, there were three more successful launches with GSLV-D2, GSLV-F01 and GSLV-F04. EDUSAT, India's first satellite dedicated for education was launched in GSLV-F01 mission. All these missions were conducted with Russian Cryo Stage.
The first indigenously developed Cryo Stage launched in GSLV-D3 could not accomplish the mission due to its turbo pump failure. After a thorough understanding of the problem and implementing the required changes, exhaustive tests including High Altitude Test of the engine were conducted. Following this, GSLV-D5 was successfully launched on January 5, 2014, with the indigenously developed cryogenic stage which placed the 1982 kg GSAT-14 satellite in to a precise Geosynchronous Transfer Orbit. The consistency in the performance of the vehicle, especially the Cryo Stage, was established with the recent spectacular success of GSLV-D6 carrying GSAT-6 satellite on August 27, 2015. All the future launches of GSLV will be with the indigenous cryogenic stage.
With two back-to-back successful missions carrying indigenous cryogenic stage, GSLV has matured into a reliable launch vehicle and has paved the way for its future operational missions, providing India self-sufficiency in launching higher capacity satellites into GTO.  The next mission, designated as GSLV-F05, is targeted for launch in July 2016 and will carry the 2200 kg INSAT-3DR meteorological satellite.  GSLV-F09 is planned in May 2017 to launch the GSAT-9 satellite.  The prestigious Chandrayaan-2 Mission is designated to be launched by GSLV in 2017-18 time frame.
GSLV is well on its way towards international and commercial operations.  Work is already in progress on the joint effort with NASA for the launch of NISAR satellite into a Polar orbit by 2020-21.  This mission will demonstrate the versatility of the GSLV for launch into various orbits.  Enquiries are also coming in for commercial launches from various countries.
While technical criticalities of the complex GSLV system have been overcome, challenges are being taken up for improving the payload capability from the present 2117 kg to the design target of 2500 kg.  Detailed studies are in progress, addressing the various ways of achieving this target.
GSLV-D1 (launched on April 18, 2001) and GSLV-D6 (launched on August 27, 2015) - being moved to Launch Pad
GSLV-D1 (launched on April 18, 2001)
GSLV-D6 (launched on August 27, 2015)