The Geosynchronous Satellite Launch Vehicle (GSLV) project has the objective of acquiring launch capability for Geo-synchronous satellites. The first flight test of the vehicle, GSLV-D1, was conducted successfully on April 18, 2001 when the 1,540 kg experimental satellite, GSAT-1, was placed in a Geo-synchronous Transfer Orbit (GTO).

GSLV-D2 is the second developmental test flight of the vehicle. In this flight GSLV will place a heavier satellite - the 1,800 kg GSAT-2 -- into Geo- synchronous Transfer Orbit of 180 km perigee (nearest point to earth) and 36,000 km apogee (farthest point to earth). The higher payload capability has been achieved by incorporating:

• enhanced propellant loading in core solid motor
• high pressure engine in liquid propellant strap-ons and second stage and
• optimisation of structural elements

The four strap-on (L40H) stages are 19.70 m long and 2.1 m in diameter. Each of them is filled with 42 tonne of hypergolic propellants (UH25) and Nitrogen Tetroxide (N₂O⁴). Each produces 765 kilo Newton thrust and burns for 149 sec.

The second stage of GSLV is 11.6 m long and 2.8 m diameter. It is filled with 39.3 tonne hypergolic propellants (UH25) and Nitrogen Tetroxide (N2O4). It produces a thrust of 804 kilo Newton. The stage burns for about 136 seconds.

The third stage of GSLV uses a Cryogenic Stage (CS) procured from Russia. The stage is 8.7 m long and 2.9 m in diameter and carries 12.6 tonne of liquid hydrogen and liquid oxygen and burns for a duration of about 705 second producing a nominal thrust of 73.5 kilo Newton.

The Payload Fairing, which is 7.8 m long and 3.4 m in diameter, protects the vehicle electronics and the spacecraft during its ascent through the atmosphere. It is discarded once the vehicle has reached an altitude of about 115 km.

Inter-stage structures, which connect different stages of GSLV, house the avionics and control systems. The vehicle equipment bay housing electronic systems like processors, navigation system, control system, guidance system, telemetry system, telecommand system, etc, is mounted above the cryogenic stage.

The spacecraft, which is mounted above the equipment bay through a payload adapter, is separated by a Merman clamp-band joint and spring mechanism that provides the required separation velocity.

The launch of GSLV is conducted from Satish Dhawan Space Centre - SHAR (SDSC- SHAR), Sriharikota, about 100 km north of Chennai. The vehicle is launched with an azimuth of 104 deg. It takes about 997 second of flight from lift-off to the injection of spacecraft into Geosynchronous Transfer Orbit. The four liquid propellant (L-40H) strap-on stages are ignited first on the launch pad. 4.8 seconds later and only after confirmation that all the four strap-on motors are developing the specified thrust, the solid propellant core stage, S139 is ignited. The core solid propellant stage burns for 107 seconds and the four L-40H propulsion stages burn up to 149 seconds by which time the vehicle would have reached an altitude of about 69 km.

The liquid propulsion second stage (GS-2) ignites 1.6 seconds before the separation of first stage. The second stage burns for about 136 seconds. About 78 seconds into the second stage propulsion, the payload fairing is separated at an altitude of about 115 km. The second stage separates at about 290 seconds from lift-off at an altitude of about 131 km.

After the separation of GS-2 stage, cryogenic stage ignites and burns for about 705 seconds. The spacecraft and the equipment bay are separated at an altitude of 198 km when they acquire the required injection velocity and the spacecraft is placed in Geo-synchronous Tranfer Orbit (GTO), with a perigee (closest point to earth) of 180 km and an apogee (farthest point to earth) of 36,000 km.

The Redundant Strap Down Inertial Navigation System/Inertial Guidance System (RESINS/(IGS), housed in the equipment bay guides the vehicle from lift-off to spacecraft injection. The digital auto-pilot and closed-loop guidance scheme ensure the required attitude maneuver and guided injection of the spacecraft to the specified orbit. The vehicle performance is monitored via telemetry at the Mission Control Centre. A telecommand system is used to terminate the flight, in case the vehicle deviates from its path beyond specified limits.

A C-band transponder on the vehicle helps in tracking it from ground based Radars. The complete telemetry and tracking of GSLV from lift-off to satellite injection is supported by four ground stations located at SDSC-SHAR , Sriharikota and the down range stations at Port Blair, Brunei and Biak in Indonesia. All these stations are networked with the SHAR Centre during launch.

GSLV consists of hundreds of sub-systems, which are designed, built, tested and qualified before the integration for launch. Most of the vehicle hardware like motor cases, inter-stages, payload fairing, engine components and electronic modules are built by Indian industry. About 150 industries, both in public and private sector, are involved. The subsystems are integrated at the various facilities of ISRO and tested before transportation to SDSC-SHAR.

The launch complex at SDSC-SHAR Centre has facilities for storage, testing and integration of the various stage elements. The launch complex houses a 75 m tall air conditioned Mobile Service Tower inside which the vehicle is integrated. In addition, the launch complex has extensive network of tracking Radars, the launch and mission control center, the facilities for spacecraft checkout and integration.

A Second launch Pad is also now under construction at SDSC-SHAR.

GSLV is the most technologically challenging project undertaken so far under the Indian space programme. It is the culmination of efforts of a large number of scientists, engineers and technicians, for over a decade. The second test flight, which will revalidate the various systems of the vehicle and the improvements carried out since the successful first launch, will herald a significant step forward in operationalising the GSLV. Having already established indigenous capability through PSLV for launching IRS class of remote sensing satellites, the GSLV, when commissioned, will make the Indian space programme a self-reliant one, while tuning it towards national development.

GSAT-2

GSAT-2 is an experimental communication satellite. The satellite will be positioned at 48 deg east longitude in the geo-stationary orbit.

GSAT-2 carries four C-band transponders, two Ku-bands transponders and a Mobile Satellite Service (MSS) payload operating in S-band forward link and C-band return link. Besides the communication payloads, GSAT-2 carries the following four piggyback experimental payloads:

• Total Radiation Dose Monitor (TRDM) to compare the estimated radiation doses inside the satellite with the directly measured radiation doses using a Radiation Sensitive Field Effect Transistor (RADFET)

• Surface Charge Monitor (SCM) to indicate the state of the charging environment in the vicinity of the spacecraft

• Solar X-ray Spectrometer (SOXS) to study the solar flare emission in 4 KeV-10 MeV energy range using state of the art semiconductor devices and Phoswich Scintillation Detector

• Coherent Radio Beacon Experiment (CRABEX) to investigate the spatial structure, dynamic and temporal variations of Ionosphere and several aspects of equatorial electrodynamics

Weighing 1800 kg at launch, GSAT-2 incorporates a 440 Newton Liquid Apogee Motor (LAM) and sixteen 22 Newton Reaction Control Thrusters for raising the satellite¡¦s orbit from Geo-stationary Transfer orbit to its final geo- stationary orbit as well as for its attitude control. It carries 840 kg of propellant (Mono Methyl Hydrazine and MON-3).

GSAT-2 will measure 9.55 m in length in its final in-orbit configuration. It will be 3-axis body stabilised using Sun and Earth Sensors, Momentum and Reaction Wheels, Magnetic Torquers and bi-propellant thrusters. Its solar array generates 1380 W power, backed up by two 24 Ah Ni-Cd batteries.

After its launch into Geo-synchronous transfer orbit by GSLV-D2, GSAT-2 will be taken to its final geo-stationary orbit by firing the liquid apogee motor in phases. After it reaches the geo-stationary orbit, its antenna and solar Panels will be deployed and the satellite will be finally placed in its allocated slot of 48 deg east longitude.