GSLV was declared operational in its present configuration (GSLV-MK I) after two successful developmental test flights conducted in April 2001 and May 2003 when it launched the 1,530 kg GSAT-1 and 1,825 kg GSAT-2 satellites into Geosynchronous Transfer Orbits (GTO). In its first operational flight, GSLV successfully launched the 1,950 kg EDUSAT into the predetermined GTO. INSAT-4C weighing 2168 kg is the heaviest satellite launched by GSLV so far.

The 49 metre tall, 414 tonne, GSLV is a three stage vehicle. The first stage, GS1, comprises a core motor with 138 tonne of solid propellant and four strap-on motors each with 42 tonne of hypergolic liquid propellants (UH25 and N204). The second stage has 39 tonne of the same hypergolic liquid propellants. The third stage (GS3) is a cryogenic stage with 12.6 tonne of Liquid Oxygen (LOX) and Liquid Hydrogen (LH2). The Aluminum alloy GSLV payload fairing is 3.4 m in diameter and is 7.8 m long.

The three-axis attitude (orientation) stabilisation of GSLV is achieved by autonomous control systems provided in each stage. Single plane Engine Gimbal Control (EGC) of the four strap-ons of the first stage are used for pitch, yaw and roll control. The second stage has Engine Gimbal Control (EGC) for pitch and yaw and hot gas Reaction Control System (RCS) for roll control. Two swivellable vernier engines using LH2 and LOX provide pitch, yaw and roll control for the third stage during thrust phase and cold gas system during coast phase. The Inertial Guidance System (IGS) in the Equipment Bay (EB) housed above the third stage guides the vehicle till spacecraft injection. The closed loop guidance scheme resident in the on-board computer ensures the required accuracy in the injection conditions. GSLV employs S-band telemetry and C-band transponders for the vehicle performance monitoring, tracking, range safety/flight safety and Preliminary Orbit Determination (POD).

GSLV employs various separation systems such as Flexible Linear Shaped Charge (FLSC) for the first stage, pyro-actuated collet release mechanism for second stage and Merman band bolt cutter separation mechanism for the third stage. Spacecraft separation is by spring thrusters mounted at the separation interface.

Satish Dhawan Space Centre (SDSC) SHAR, located on the east coast of India is the launch station for all satellite launch vehicles of India. Sriharikota was selected as the launch site to take advantage of the earth's rotation and other factors affecting the flight of a launch vehicle.

Cryogenic Stage: The third stage of GSLV is cryogenic. The cryogenic stage is much more efficient and provides more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellants. Specific impulse (a measure of the efficiency) achievable with cryo fluids (liquid Hydrogen and liquid Oxygen) is of the order of 450 sec compared to 300 sec for earth storable and solid fuels, giving a substantial payload advantage; for an upper stage, with every one second increase in the specific impulse, the payload gain is of the order of 10 kg.

However, cryogenic stage is technically a very complex system compared to solid or earth-storable liquid propellant stages due to the use of propellants at extremely low temperatures and the associated thermal and structural problems. Oxygen becomes a liquid at -183 deg C and Hydrogen liquefies at -253 deg C. The propellants, at these low temperatures, are to be pumped using turbo pumps running at 42,000 rpm. It also entails complex ground support systems like propellant storage and filling systems, cryo engine and stage test facilities, transportation and handling of the cryo fluids and related safety aspects. While the initial flights of GSLV are using the Russian supplied cryogenic stage, the indigenous development of the cryo stage has reached an advanced stage with the engine having already been qualified and the stage systems tests planned in the coming months.

Satellite Launch Vehicle Development in India

The realisation of a satellite launch vehicle involves many branches of science and engineering, sophisticated infrastructure and innovative management techniques. Even today, only a few countries possess the technology of to successfully build satellite launch vehicles. The subsystems in a launch vehicle should withstand hostile flight environment, should be of light weight, cost effective and should be realisable within a reasonable time. Years of developmental efforts are put to test in a few minutes of flight requiring performances with practically no margin for error.

In India, rocket development began in 1963 with the establishment of Thumba Equatorial Rocket Launching Station near Thiruvananthapuram for carrying out scientific experiments in aeronomy and astronomy using rockets built abroad. India's first indigenous sounding rocket was a small 75 mm diameter Rohini, RH-75. Today, India operates a family of sounding rockets of diameters ranging from 200 to 560 mm and capable of carrying upto 200 kg payload to an altitude of 300-400 km to conduct scientific experiments. 45 sounding rockets were flown on consecutive days during February-March 2000 for a major scientific campaign, Equatorial Wave Campaign.

SLV-3: SLV-3, India's first experimental satellite launch vehicle, was successfully launched for the first time on July 18, 1980 from SHAR Centre (which was renamed as Satish Dhavan Space Centre SHAR in 2002), Sriharikota and it placed a Rohini Satellite, RS-1 in orbit. The first experimental flight of SLV-3 had taken place in July 1979 but the mission was only partially successful due to a jammed valve in the second stage control system resulting in the leak of the oxidiser. After the successful second flight, two more flights of SLV-3 were conducted in May 1981 and April 1983 to place Rohini satellites carrying remote sensing cameras on board. Conceived in 1969, SLV-3 was a 22 metre long, four-stage vehicle weighing 17 tonne. All its stages used solid propellant and it employed open loop guidance with stored pitch programme to steer the vehicle in flight along the pre-determined trajectory. SLV-3 provided valuable inputs for the vehicle and mission design, materials, hardware fabrication, realisation of solid propellant technology, control power plants, staging systems, inertial sensors, electronics, testing, integration and checkout and launch complex establishment at Sriharikota with associated ground instrumentation.

ASLV: Keeping in view the long term goal for realising polar and geosynchronous launch capability for operational class of satellites, the development of Augmented Satellite Launch Vehicle (ASLV) was undertaken for demonstrating critical technologies. ASLV was configured as a five stage solid propellant vehicle, weighing about 40 tonne and having a length of about 23.8 m. The strap-on stage consisted of two identical 1 m diameter solid propellant motors similar to SLV-3 first stage, other stages being the same as in SLV-3. Closed loop guidance, active from the ignition of the second stage motor to the separation of the third stage, was employed in ASLV while SLV-3 had used an open loop guidance system.

The first developmental flight test of ASLV took place in March 1987 but the mission did not succeed due to non-ignition of the first stage motor after the strap-on stage burn out. The second flight, ASLV-D2, took place in July, 1988. This mission also did not succeed. After a detailed failure analysis, a number of corrective actions were taken, many of them relating to the transition between the strap-on stage and the first stage. With the incorporation of all the modifications, the third developmental flight, ASLV-D3, was successfully conducted on May 20, 1992 when SROSS-C satellite, carrying a Gamma- ray burst detector and an aeronomy payload was placed in orbit. Another flight of ASLV (ASLV-D4) was conducted on May 4, 1994 when a 113 kg SROSS-C2 satellite was put into a low earth orbit. ASLV provided valuable inputs to the development of PSLV.

PSLV: The Polar Satellite Launch Vehicle (PSLV) project was initiated in 1982. In the present configuration (employed in PSLV-C5), the 44.4 metre tall, 295 tonne PSLV, has four stages using solid and liquid propulsion systems alternately. While the first developmental launch of PSLV (PSLV-D1), on September 20, 1993 did not fulfill the mission of injecting the IRS-1E satellite into orbit, most of the PSLV systems performed normally. The failure of this flight was primarily due to a software error in the pitch control loop of the on-board guidance and control processor, and the failure of two small retro rockets leading to a contact between second and third stages during the separation of the second stage. The second developmental flight, PSLV-D2, on October 15, 1994, was successful when the vehicle injected the 804 kg remote sensing satellite, IRS-P2, into the desired orbit. During the third developmental test flight conducted on March 21, 1996, PSLV could place a 922 kg IRS-P3 satellite in the intended 817 km polar orbit. With these two consecutive successes, PSLV became operational.

Several more improvements have been incorporated in the vehicle since then. The major improvements include: increasing the solid propellant in the first core stage from 128 tonne to 138 tonne; increasing the liquid propellant loading in the second stage from 37.5 tonne to 40.6 tonne by stretching the stage tankages; replacing the metallic payload adopter by a CFRP adopter and; effecting weight reduction in the vehicle equipment bay. Besides, four of the six strap-on motors are ignited on the ground along with the core first stage; in the earlier flights only two were ignited on the ground and the remaining four a few seconds after lift-off.

In its first operational flight, PSLV successfully placed the 1200 kg Indian Remote Sensing satellite, IRS-1D, into a polar orbit. Later it launched OCEANSAT-1 (IRS-P4), TES, RESOURCESAT-1, CARTOSAT-1 and HAMSAT into the predetermined polar orbits in 1999, 2001, 2003 and 2005 respectively. PSLV has now become a workhorse launch vehicle for polar satellites and it is now offered for carrying satellites of other space agencies also. So far it had seven successful flights. PSLV has also been used for launching a geo-synchronous satellite - India's first exclusive meteorological satellite, KALPANA-1, in September 2002. It has also launched four satellites of other space agencies - KITSAT-3 of Korea, DLR-TUBSAT and BIRD of Germany and PROBA of Belgium. Three more satellites LAPAN TUBSAT of Indonesia, X-Sat of Nanyang Technological University, Singapore and Agile of Italy are already in the pipeline. Of these, LAPAN TUBSAT will be flown along with India's CARTOSAT-2 and Space Capsule Recovery Experiment (SRE-1) on board PSLV-C7 this year.

GSLV: GSLV, in its very first developmental test flight on April 18, 2001, succeeded in placing an experimental communication satellite, GSAT-1, into a Geosynchronous Transfer Orbit(GTO). It was declared operational after its second successful developmental test flight on May 8, 2003, when it placed GSAT-2 into its intended GTO. During its first operational flight (GSLV-F01) on September 20, 2004, GSLV launched the 1950 kg EDUSAT, India's first exclusive satellite for the educational sector.

While in the present configuration (GSLV Mk I), GSLV is capable of placing 2,000 kg class satellites into GTO, once its Russian supplied upper stage is replaced by the ISRO developed Cryogenic stage (GSLV-Mk II), it will be able to place 2,500 kg class satellites into GTO. GSLV Mk III will be capable of placing a 4 tonne satellite into GTO. It will have a 110 tonne core liquid propellant stage, two 200 tonne solid propellant strap-on motors and a 25 tonne cryogenic stage.

INSAT-4C

INSAT-4C is the second satellite in the INSAT-4 series. The first, INSAT-4A, was launched in December 2005. INSAT-4C carries 12 high-power Ku-band transponders designed to provide Direct-To-Home (DTH) television services, facilitate Video Picture Transmission (VPT) and Digital Satellite News Gathering (DSNG) as well as to serve National Informatics Centre (NIC) for its VSAT connectivity. The 2,168 kg INSAT-4C is launched in the second operational flight of India's Geosynchronous Satellite Launch Vehicle, GSLV-F02. The satellite is designed for a mission life of ten years.

INSAT system was established in 1983. With nine satellites - INSAT-2E, INSAT-3A, INSAT-3B, INSAT-3C, INSAT-3E, INSAT-4A, GSAT-2, EDUSAT and KALPANA-1 in service with a total of 175 transponders in Ku-band, C-band and Extended C-band besides instruments for meteorological imaging and data relay functions, INSAT is the largest domestic communication satellite system in the Asia-Pacific region. INSAT-4C, once commissioned, will further augment the INSAT system capacity.

Soon after its injection into Geosynchronous Transfer Orbit (GTO) orbit by GSLV-F02, the solar panels of INSAT-4C will be deployed. In the following days, the satellite is manoeuvred to its 36,000 km high Geo-Synchronous orbit (GSO) by firing Liquid Apogee Motor (LAM) on board the satellite. In GSO, INSAT-4C will be co-located with INSAT-3C, KALPANA-1 and EDUSAT at 74 degree East Longitude.

Salient features:

Orbit : Geostationary (74 degree East Longitude)

Co-located with INSAT-3C, KALPANA-1 and EDUSAT

Lift-off Mass : 2,168 kg

Dry Mass : 950 kg

Physical : 1.650 x 1.535 x 2.406 m cuboid 9.45 m long with solar panels deployed

Propulsion and : 440 Newton Liquid Apogee Motor (LAM) with Control

Mono Methyl Hydrazine (MMH) as fuel and Mixed Oxides

of Nitrogen (MON-3) as oxidizer for orbit raising

3-axis body stabilized in orbit using earth sensors,

momentum and reaction wheels, magnetic torquers and

eight 10 Newton and eight 22 Newton bi-propellant thrusters

Power : Solar array providing 2870 W ;Two 70 Ampere-hour

Nickel-Hydrogen Batteries

Antennas : 2.2 m X 2.2 m diameter deployable reflector for

transmit functions 1.4 m diameter deployable reflector for

receive functions

Mission : 10 years

Communication Payloads:

- 12 Ku-band 36 MHz bandwidth Transponders employing 140 W Travelling Wave Tube Amplifiers (TWTAs) to provide an Effective Isotropic Radiated Power (EIRP) of 51.5 dBW at Edge of Coverage (EOC) with footprint covering Indian mainland

- Ku-band Beacon as an aid to users to lock on to the satellite signal