First Developmental Test Flight of Geosynchronous Satellite Launch Vehicle (GSLV)

Mission Objective

The Geosynchronous Satellite Launch Vehicle (GSLV) project was initiated in 1990 with the objective of acquiring launch capability for Geo-synchronous satellites. The first flight test, GSLV-D1, is intended to validate the various systems of the vehicle in an actual flight. Though each of the subsystems has been tested on ground, it is only through a few developmental flight tests that the launch vehicle, as a whole, and all the associated ground systems can be validated. Several performance parameters of propulsion stages, avionics, control and guidance system, the stage and spacecraft separation system, will be monitored in flight. The design margins will be more realistically estimated from the in-flight test of the vehicle.

In the first developmental test flight, GSLV, will place a 1,540 kg experimental satellite, GSAT-1, in a Geo-synchronous Transfer Orbit (GTO).

GSLV Configuration

In its present configuration, GSLV, is a three-stage vehicle. It is 49 m tall and weighs about 401 tonne at lift-off. The vehicle configuration makes use of several systems that have been flight proven through India's Polar Satellite Launch Vehicle, PSLV. The first stage solid propellant motor and the liquid propellant second stage of PSLV have been employed as the core first stage motor and the second stage of GSLV. The first stage liquid strap-on stages are also derived from the second stage of PSLV.

GSLV Stages

The first stage of GSLV comprises a solid propellant motor (S125) and four liquid propellant strap-on motors (L40). S125 stage is 20.3 m long and 2.8 m in diameter. Its motor case is made of high strength steel. It carries 129 tonne of Hydroxyl Terminated Poly Butadiene (HTPB) based solid propellant. The stage develops about 4700 kilo Newton thrust and burns for 100 seconds. The four strap-on (L40) stages are 19.70 m long and 2.1 m in diameter and they are fabricated using aluminum alloy. Each of them is loaded with 40 tonne of hypergolic propellants, namely, Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen Tetroxide (N2O4) as oxidizer, stored in two tanks mounted in tandem.

The second stage of GSLV is 11.6 m long and 2.8 m diameter. It is loaded with 37.5 tonne of UDMH and N2O4 in two compartments of an aluminum alloy tank separated by a thin metal sheet known as common bulkhead. The engines used for the strap-on motors and the second stage are similar and employ a turbo-pump fed engine producing a thrust of about 700 kilo Newton in vacuum. Due to the larger propellant loading, the strap-on stages burn for about 160 seconds while the second stage burns for 150 seconds.

The third stage of GSLV uses a Cryogenic Stage (CS) procured from Glavkosmos, Russia. The stage, that employs liquid hydrogen and liquid oxygen as fuel and oxidizer respectively, is 8.7 m long and 2.9 m in diameter. Liquid hydrogen (LH) and liquid oxygen (LOX) are stored in two separate aluminum alloy tanks connected by an inter-stage structure. With a propellant loading of 12.5 tonne, the stage can burn for a duration of about 750 second producing a nominal thrust of 75 kilo Newton.

Auxiliary Systems

The different stages of GSLV are connected by inter-stage structures, which also house the necessary avionics and control systems for controlling the lower stage till it is separated. The vented inter-stage between the first and second stage, enables the firing of the second stage even while the first stage has just completed its thrusting action. This design avoids use of additional systems needed to provide sufficient acceleration between the time before the ignition of second stage takes place and sufficient reduction in velocity of the first stage. The first stage, including the core and four strap on motors after its function, is separated from the rest of the vehicle using a flexible linear shaped charge (FLSC) that is severs the connection between first and second stages.

The vehicle equipment bay housing the vehicle electronic systems like processors, navigation system, control system, guidance system, telemetry system, telecommand system, etc, is housed in a truss structure above the cryogenic stage. The spacecraft is mounted above the equipment bay through a payload adapter and separation system

A heatshield, which is 7.8 m long and 3.4 m in diameter, protects the vehicle electronics and the spacecraft from the hostile environment during the ascent flight through the atmosphere. The heatshield is discarded at about 110 km during the second stage propulsion.

The spacecraft is separated by opening the band-clamp joint and the springs attached within the separation system that provides the required separation velocity to the satellite. The system is designed to ensure that no collision occurs between the spent third stage and the spacecraft.

Mission Sequence

The launch of GSLV is conducted from Satish Dhawan Space Centre, SHAR, Sriharikota, about 100 km north of Chennai. The vehicle is launched at an azimuth of 104O. It takes about 1040 second for the flight from lift-off to the injection of spacecraft into Geosynchronous Transfer Orbit. About 150 critical events have to be gone through during the flight, before the satellite is placed in orbit. The nominal mission sequence is as follows:

On the launch pad, the four liquid propellant (L-40) strap-on stages are ignited first. The solid propellant core stage, S125, is ignited 4.6 seconds later, after confirming the normal operation of each of the L-40 stages. The core solid propellant stage burns for 100 seconds and the four L-40 propulsion stages continue to burn upto 160 seconds by which time the vehicle would have reached an altitude of about 73 km.

The liquid propulsion second stage (GS-2) ignites 1.6 seconds before the separation of first stage. The second stage carries 37.5 tones of propellant which it burns in about 150 second. About 100 seconds into the second stage propulsion, the Heat shield, which protects the spacecraft and equipment is separated. By this time, the vehicle would have reached an altitude of about 115 km. The separation of the second stage takes place at about 314 seconds from lift-off at an altitude of about 127 km.

After the separation of GS2 stage, cryogenic stage ignites and this stage burns for about 710 second. The spacecraft and the equipment bay are separated at an altitude of 195 km. Before separation, it gives the spacecraft the required injection velocity of 10.2 km per second to place it in the Geo-synchronous Tranfer Orbit (GTO), which is a highly elliptical orbit with a perigee (closest to the earth) of 180 km and an apogee (farthest to the earth) of 35,975 km. After injection of the spacecraft, the Cryogenic Stage is passivated by venting all onboard tanks and gas bottles and the stage is re-oriented so as to avoid any possible collision with the spacecraft.

Avionics

The inertial navigation and guidance system Redundant Strap Down Inertial Navigation System/Inertial Guidance System (RESINS/(IGS) which is housed in the equipment bay computes the inertial position and velocity and guides the vehicle from lift-off to spacecraft injection. The digital auto-pilot and closed-loop guidance scheme resident in the on-board computer ensure the required attitude maneuver and guided injection of the spacecraft to the specified orbit.

The vehicle performance is monitored with extensive instrumentation. The performance data is transmitted via telemetry systems to the ground station. In addition to the performance parameters, the inertial position of the vehicle and its orientation are computed by the vehicle inertial system and computers which are also transmitted via the telemetry to the ground stations. A telecommand system is used to terminate the flight, in case the vehicle deviates from its flight path beyond the specified limits.

A C-band transponder on the vehicle helps in tracking it from ground based radars. The complete telemetry and tracking coverage of the vehicle from lift-off to satellite injection will be provided by four ground stations located at Satish Dhawan Space Centre, SHAR, Sriharikota, the down range stations at Port Blair, Brunei and Biak in Indonesia. All these stations are networked with the Satish Dhawan Space Centre, SHAR during launch to provide data in real time. The vehicle undergoes checks at every stage of integration, followed by checks on the integrated vehicle along with the satellite and a launch rehearsal is also gone through.

New Elements in GSLV compared to PSLV

In addition to the cryogenic stage, the other major new elements in GSLV, are the liquid strap-on stages, a heat shield with larger diameter than PSLV (3.4 m compared to 3.2 m in PSLV) and the vented inter-stage between first and second stage. Mission design and simulations, realization of test and launch complex facilities including servicing of cryogenic stages, launch hold and release mechanism, etc, were also involved in GSLV.

General

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

Launch Complex

The launch complex at Satish Dhawan Space Centre, SHAR has facilities for storage, testing and integration of the various stage elements. The launch complex houses a 75 m tall 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.

The launch facilities at Satish Dhawan Space Centre, SHAR have been suitably modified to launch both PSLV and GSLV. A Second launch Pad is also now under construction to enable more frequent launches.

Operationalisation of GSLV

GSLV will be declared operational after two successful developmental flights. Efforts are already on to improve the payload in GTO up to 2000 kg and beyond in about 2 or 3 years. Other than GTO missions, GSLV can also perform mission to LEO and polar missions.

Conclusion

GSLV is the most technologically challenging mission undertaken so far under the Indian space programme. It is the culmination of efforts of a large number of scientists, engineers and technicians, over the last ten years. The mission will herald a significant milestone towards the establishment of indigenous capability for launching communication satellites like INSAT. Having already established indigenous capability for launching IRS class of remote sensing satellites through PSLV, the launch of GSLV will fulfill the vision of Dr Vikram Sarabhai to make the Indian space programme a self-reliant one, while tuning it towards national development.

GSAT-1

While the first developmental test flight is primarily intended for validating the vehicle design and its performance parameters as well as the associated ground infrastructure, the flight opportunity is also made use of to place an experimental satellite GSAT-1 weighing about 1540 kg.. GSAT-1 will be used to prove new spacecraft elements like ten Newton Reaction Control Thrusters, Fast Recovery Star Sensors and Heat Pipe Radiator Panels to validate them before using them in the ISRO operational ISRO satellites like IRS and INSATs. GSAT-1 will also carry two C-band transponders employing 10W Solid State Power Amplifiers (SSPAs), one C-band transponder using 50 W Travelling Wave Tube Amplifier (TWTA) and two S-band transponders using 70W TWTA.

GSAT-1 will be used for demonstrating digital audio broadcast, internet services, compressed digital TV experiments and developmental communication.

Cryogenic Stage

GSLV employs a cryogenic stage. It is for the first time that a cryogenic stage is being employed in an ISRO vehicle. 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 achievable with cryo fluids (liquid hydrogen and liquid oxygen) is of the order of 450 sec compared to 300 sec of earth storable and solid fuels, giving a substantial payload advantage; for every one second increase in the specific impulse, the payload gain is of the order of 10 kg.

However, cryogenic stage is technically very complex system compared to solid or earth-storable liquid propellant systems due to the use of propellants at extremely low temperatures and the associated thermal and material problems. The temperature of Liquid Hydrogen is -253 deg C and that of liquid oxygen is -195 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 fill systems, cryo engine and stage test facilities, transportation and handling of the cryo fluids and related safety aspects.

While the initial flights of GSLV will use Russian supplied cryogenic stage, a project CUSP has already been initiated to develop the stage indigenously. The first in a series of tests of an indigenous engine developed under this project was conducted in February 2000 for 15 seconds. Further tests are planned in the coming months.

Launch Vehicle Development in India

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

SLV-3: SLV-3, India's first experimental satellite launch vehicle. It was first successfully launched on July 18,1980 from Satish Dhawan Space Centre, SHAR, Sriharikota when a Rohini satellite, RS-1, was placed 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 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 sensors 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 pre-determined trajectory. SLV-3 gave 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.

Sriharikota island, located at 13 degree N latitude, was selected as the launch site for SLV-3 and for all subsequent launch vehicles, to take advantage of the earth's rotation and other advantages.

ASLV: Keeping in view the long term goal for realising polar and geosynchronous launch capability for operational class of satellites, development of Augmented Satellite Launch Vehicle (ASLV), was undertaken to act as a low cost intermediate vehicle for demonstrating critical technologies. ASLV was configured as a five stage solid propellant vehicle, eighing 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 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, ASLV-D2, was launched on 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. They also included better characterization of vehicle, improved stability, introduction of on-board detection of flight events and extensive simulations.

With the incorporation of all the above 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 the intended orbit. Another launch 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 (PSLV-C1), the 44.4 metre tall, 294 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 orbits. During the third developmental test flight, 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 an operational vehicle.

Several improvements were incorporated in the first operational flight of PSLV (PSLV-C1) to increase its payload capability to 1,200 kg. The major improvements included: 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, in the PSLV-C1 mission, four of the six strap-on motors were ignited on the ground along with the core first stage; in the earlier flights only two were ignited on the ground and the remaining a few seconds after lift-off. This revised sequence gave a substantial payload advantage.

In its first operational flight, PSLV successfully placed the Indian Remote Sensing satellite, IRS-1D, into polar orbit. In its second operational flight on May 26, 1999, PSLV, placed the Indian remote sensing satellite, IRS-P4, along with two satellites -- the KITSAT of Korea and DLR-TUBSAT of Germany -- into the precise sun synchronous polar orbit.

PSLV has thus become a workhorse launch vehicle for polar satellites and it is now offered for carrying satellites of other space agencies also. A satellite, BIRD, from German space agency, DLR and another PROBA of a Belgian company are scheduled for launch along with India's TES satellite on board PSLV in 2001-02. PSLV is also planned to be used for geo-synchronous satellite mission and the first such mission will be when it launches India's meteorological satellite, METSAT, in 2002.

PSLV has proved several systems that are now employed in GSLV. Several facilities, established for PSLV, are also used by GSLV, with modifications where required.

Indian Launch Vehicles