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SLV

The successful launch of India’s first Satellite Launch Vehicle (SLV-3) on July 18, 1980, was a historic landmark for the Indian space programme. The maiden national launch vehicle effort, SLV-3, gave ISRO a remarkable insight into the conceptualisation, design, development and management of a technically complex multi-disciplinary project as the young team was experimenting with and learning the nuances of launch vehicle technology.

The next logical corollary to Sounding rockets, was the development of a satellite launch vehicle. Realisation of the launch vehicle is a sophisticated technology by itself and the related infrastructure was required to be built in the areas of propellant, propulsion, avionics, materials, motor testing, vehicle assembly, vehicle checkout and ground telemetry/tracking. ISRO establishments in the country were geared to these mammoth efforts through time bound projects. Vikram Sarabhai Space Centre (VSSC) is responsible for launch vehicle design, development and management. Sriharikota is a launch base. It also houses propellant production and rocket motor test facilities, ISRO Satellite Centre (ISAC) specialises in building spacecrafts. Space Application Centre (SAC), Ahmedabad, has the primary task of applying the space technology for the socio-economic benefit of the nation.

The SLV-3 was to have four stages, all powered by solid propellants. Vikram A. Sarabhai handpicked four young scientists working with him to entrust the task of designing each of these stages. In addition to Gowariker and Muthunayagam, M R Kurup and A P J Abdul Kalam, who later became the chief architect of Indian guided missile programme and later the Scientific Adviser to the Defence Minister and head of the Defence Research Development Organisation (DRDO), were drafted in.

Untimely death of Vikram A. Sarabhai on December 30, 1971, at the age of 52, was a major blow to the Indian space program. A visionary par excellence, Sarabhai’s contribution to diverse fields such as science, business and administration was unparallel in the Indian history.

After Sarabhai, Prof. Satish Dhawan, then the director of Indian Institute of Science (IISc), Bangalore, took over the charge of the Indian space programme, even though Prof. M G K Menon was at the helm of affairs for a brief period of six months. In June 1972, the Department of Space and the Space Commission were set up. And ISRO was brought under the Department of Space. If the Indian space program owed its birth to the vision of Sarabhai, it was Prof. Dhawan who gave muscles and sinews to the programme. Under Prof. Dhawan, Sarabhai’s vision crystallised into a series of successful missions. The first one to be so was the SLV-3 project.

By late 1973, designs of several subsystems that were to go into SLV-3 were finalised and the project was conceived as a major national venture involving some 46 organisations in both public and private sectors. Abdul Kalam, whose team successfully designed the composite fourth stage for SLV-3, was appointed as the project director of the programme. Though originally a four- year schedule had drawn up for the first experimental flight, it took good six years to complete. It had taken approximately seven years to realise the vehicle from start.

SLV-3 is a four stage solid propulsive vehicle designed and developed by VSSC.This vehicle with a lift off weight of 17 tonnes and total length of 22 meters can impart the required velocity of 28000 km/hr to 35 kg satellite to inject the same into a low earth elliptical orbit. SLV-3 consists of forty four major functional subsystems.

The Vehicle Propulsive System forms the main ‘muscle’ for achieving the required altitude and velocity for orbital injection. The four stages are solid propellant type. The first stage is of 1000 mm diameter and carries 8.6 tonnes of PBAN (Polybutadine Acrylo Nitrate) propellant developed indigenously. The motor case fabricated from 15 CDV6 steel sheets and forgings is in three longitudinal segments. Propellant is cast separately in each segment and then joined together. The segmented motor technology has been specifically developed for the first stage motor. This motor develops an average thrust of 46 tonnes and burns for 50 seconds. with a specific impulse value of 254 seconds (vacuum).

The second stage motor is of 800 mm diameter and carries 3 tonnes of PBAN propellant in a single monolithic grain. This motor is also made of 15 CDV6 steel sheets and forgings. The motor has an average thrust of 20 tonnes and burns for 44 seconds and gives a specific impulse of 268 seconds (vacuum). The third and fourth stage motors use fibre reinforced plastic motor cases and high energy propellant (HEF 20) developed inhouse. Third stage with a diameter of 800 mm houses one tonne of propellant and gives an average thrust of 6.3 tonnes. Fourth stage has a diameter of 650 mm, carries 262 kg propellant and provides a thrust of 2.4 tonnes. The specific impulse of fourth stage is 284 seconds (vacuum). Numbers of tests have been carried out both in scaled down size and in full scale to confirm the reliability of performance of individual stage motors.

Rocket systems comprise stage separation systems, destruct system and heat-shield. The separation between the stages is carried out by initiating “Flexible Linear Shaped Charge” (FLSC) system located between the stages for the first two stages. Ball type separation system is employed for third and fourth stages. Fibreglass honeycomb heatshield is provided around satellite and fourth stage to protect them from aerodynamic heating during atmospheric flight region. After the vehicle crosses the dense atmosphere, the heat-shield is separated from the vehicle at an altitude of about 85 km. Also FLSC type destruct systems are housed in first three stages to destruct the vehicle based on ground command in the event of vehicle deviating from specified flight path.

Guidance and Control System Guidance and control system of the vehicle is responsible for three axis stabilisation and for steering the vehicle along the preset trajectory profile. The system mainly does three functions: Sense the inertial attitude of the vehicle; Generate suitable control function to actuate the control power plants; and Generate appropriate control forces to stabilise and steer the vehicle.

Four gimbal stabilised inertial platform is used to sense the vehicle attitude. Autopilot compares attitudes with command angles as given by pitch programme stored in vehicle attitude programmer and with launch references for yaw and roll axes. The error signals thus generated are mixed with vehicle body rates measured by rate gyro package to generate command signals for control systems.

For the first stage, Secondary Injectant Thrust Vector Control system (SITVC) in proportional mode has been employed (using strontium perchlorate as injectant) for the first 17 seconds of flight, for pitch and yaw control. For roll control throughout and pitch and yaw control beyond 17 seconds electrohydraulically operated aerodynamic control surfaces (fin tip control) are used. For the second stage, bipropellant on-off reaction control power plant (using RFNA and hydrazine) is used for pitch, yaw and roll control, both in power and coast phase.

The third stage has monopropellant on-off reaction control system (using hydrazine and indigenously developed catalyst), to generate control forces required during third stage flight regime. The fourth stage is spin stabilised. SITVC control system has been evaluated in the static test of first stage motor. Second and third stage control systems have undergone a number of system level ground tests. In addition to computer simulation, the total guidance and control chain has also been tested in the hardware in the loop simulation checks.

The telemetry, telecommand, tracking and sequencing system constitute the vehicle electronics systems.During flight the health and performance of vehicle systems are monitored by telemetry system. This employs two schemes – one FM/FM and the other PCM/FM – accommodating about 400 vehicle parameters like motor pressures, temperature, guidance commands, attitude errors. Onboard tracking subsystem includes C-band transponder and tone range receiver. Vehicle sequencer generates actuation commands for stage ignition, separation and control system gain change. Redundant telecommand receivers are provided onboard to execute ground commands for destruction, if required.The equipment bay – the brain of the vehicle housing most of the guidance and electronic subsystems is located just above third stage.

The integration of nearly one lakh individual parts of the vehicle into components, subsystems, subassemblies, stages and vehicle is an arduous task, spanning over more than a year. The four rocket motors are processed at VSSC/SHAR. The other eight interstage subassemblies housing control systems, equipment bay, separation system, electronic monitoring/interface circuits are integrated and checked out at Vehicle Integration Laboratory/Electronic Checkout Laboratory, VSSC, before being transported to SHAR. The checkout process, conceived in four phases, is carried out for components, individual subassemblies, electrically interfaced stages and fully integrated vehicle.

The various subassemblies and rocket motors are brought to SLV-3 Complex which consists of a Vehicle Integration Building, Block House, Launcher and other facilities such as pneumatic sources. During this period, commonly known as launch campaign, the vehicle is built up in stages, with a concurrently running checkout from Block House. Block House is nearly midway between vehicle integration building and launcher and connected with them through 1000 lines of checkout cable.

After integration and checkout of the vehicle at integration building, it moves to launch pad. The final count down of the vehicle, in conjunction with ground stations spans over more than 23 hrs, preceded by a rehearsal. The last 11 minutes of operations are entirely taken over by checkout computer at Block House. Nearly 600 parameters are checked during this phase and the computer clamps down a hold if the monitored parameters do not fall within set limits.

The first flight of SLV-3 on August 10, 1979, however, was only partially successful. India's capability in the launch vehicle technology was first demonstrated through the successful launch of SLV-3 in July 1980, which placed a 40 kg Rohini satellite into a near-earth orbit. Two more launches of SLV-3 were conducted in May 1981 and April 1983 with the Rohini satellites.

The Satellite Launch Vehicle (SLV) Programme was born out of the need for developing indigenous satellite launch capability for communications, remote sensing and meteorology. Satellite Launch Vehicle-3 (SLV-3) was India's first experimental satellite launch vehicle, which was an all solid, four stage vehicle weighing 17 tonnes with a height of 22m and capable of placing 40 kg class payloads in Low Earth Orbit (LEO).

SLV-3 was successfully launched on July 18, 1980 from Sriharikota Range (SHAR), when Rohini satellite, RS-1, was placed in orbit, thereby making India the sixth member of an exclusive club of space-faring nations. SLV-3 employed an open loop guidance (with stored pitch programme) to steer the vehicle in flight along a pre-determined trajectory. The first experimental flight of SLV-3, in August 1979, was only partially successful. Apart from the July 1980 launch, there were two more launches held in May 1981 and April 1983, orbiting Rohini satellites carrying remote sensing sensors. The successful culmination of the SLV-3 project showed the way to advanced launch vehicle projects such as the Augmented Satellite Launch Vehicle (ASLV), Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous satellite Launch Vehicle (GSLV).