PSLV-C4 is the seventh flight of Polar Satellite Launch Vehicle (PSLV) and its
first flight to place a satellite - the 1060 kg METSAT - into a Geosynchronous
Transfer Orbit (GTO). Initially, PSLV was designed for launching 900 kg Indian
Remote Sensing Satellites (IRS) into a 900 km polar Sun Synchronous Orbit.
Since its first launch in 1993 from Sriharikota, the four stage PSLV has been
successively improved to enhance its capability.
Compared to the earlier PSLV launches, The flight path of PSLV-C4 has been modified to inject the METSAT into a Geosynchronous Transfer Orbit of 250 km perigee (nearest point to Earth) and 36,000 km apogee (farthest point to Earth). This orbit will be elliptical in shape and will be inclined at angle of 18 degrees to the equator.
In its present configuration, the 44.4 metre
tall, 295 tonne PSLV has four stages using solid and liquid propulsion systems
alternately. The first stage is one of the largest solid propellant boosters in
the world and carries 138 tonnes of Hydroxyl Terminated Poly Butadiene (HTPB)
based propellant. It has a diameter of 2.8 m. Its motor case is made of
maraging steel. The booster develops a maximum thrust of about 4,628 kilo
Six strap-on motors, four of which are ignited on the ground, augment the first stage thrust. Each of these solid propellant strap-on motors carries nine tonne of HTPB based propellant and produces 662 kN thrust.
The second stage employs indigenously built Vikas engine and carries 40 tonne of liquid propellant -- Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen tetroxide (N2O4) as oxidiser. It generates a maximum thrust of about 725 kN.
The third stage uses 7.6 tonne of HTPB-based solid propellant and produces a maximum thrust of 260 kN. Its motor case is made of polyaramide fibre.
The fourth and the terminal stage of PSLV has a twin engine configuration using liquid propellant. With a propellant loading of 2.5 tonne (Mono-methyl hydrazine as fuel and Mixed Oxides of Nitrogen as oxidiser), each of these engines generates a maximum thrust of 7.4 kN.
The 3.2 m diameter metallic bulbous heat-shield of PSLV, which is made of isogrid construction, protects the spacecraft during the PSLV's passage through the dense atmosphere.
PSLV flight control system includes: a) First stage: Secondary Injection Thrust Vector Control (SITVC) for pitch and yaw, reaction control thrusters for roll and SITVC in two strap-on motors for roll control augmentation, b) Second stage: Engine gimbal for pitch and yaw and, hot gas reaction control for roll, c) Third stage: flex nozzle for pitch and yaw and PS-4 RCS for roll and d) Fourth stage: Engine gimbal for pitch, yaw & roll and on-off RCS for control during the coast phase.
PSLV's Inertial Navigation System (INS) is situated in its equipment bay, which is located on top of the vehicle's fourth stage. INS guides the vehicle from lift-off to spacecraft injection into orbit.
The PSLV is provided with instrumentation to monitor the vehicle performance during the flight. S-band PCM telemetry and C-band transponders cater to this requirement. The tracking system provides real-time information for flight safety and for preliminary orbit determination once the satellite is injected into orbit.
PSLV employs a large number of stage auxiliary systems for stage separation, heat shield separation and jettisoning, etc.