Vehicle Description
The PSLV has four stages using solid and liquid propulsion systems alternately. The first stage is one of the largest solid-fuel rocket boosters in the world and carries 138 tonnes of Hydroxyl-terminated polybutadiene (HTPB) bound propellant with a diameter of 2.8 m. The motor case is made of maraging steel. The booster develops a maximum thrust of about 4,430 kN. 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 tonnes of HTPB propellant and produces 677 kN thrust. Pitch and yaw control of the PSLV during the thrust phase of the solid motor is achieved by injection of an aqueous solution of strontium perchlorate in the nozzle to constitute Secondary Injection Thrust Vector Control System (SITVC). The injection is stored in two cylindrical aluminum tanks strapped to the solid rocket motor and pressurized with nitrogen. There are two additional small liquid engine control power plants in the first stage, the Roll Control Thrusters (RCT), fixed radially opposite one on each side, between the triplet set of strap-on boosters. RCT is used for roll control during the first stage and the SITVC in two strap-on motors is for roll control augmentation.
The second stage employs the Vikas engine and carries 41.5 tonnes (40 tonnes till C-5 mission) of liquid propellant – Unsymmetrical Di-Methyl Hydrazine (UDMH) as fuel and Nitrogen tetroxide (N2O4) as oxidizer. It generates a maximum thrust of 800 kN (724 till C-5 mission). Pitch & yaw control is obtained by hydraulically gimbaled engine (±4°) and two hot gas reaction control for roll.
The third stage uses 7 tonnes of HTPB-based solid propellant and produces a maximum thrust of 324 kN. It has a Kevlar-polyamide fiber case and a submerged nozzle equipped with a flex-bearing-seal gimbaled nozzle (±2°) thrust-vector engine for pitch & yaw control. For roll control it uses the RCS (Reaction Control System) of fourth stage.
The fourth and the terminal stage of PSLV has a twin engine configuration using liquid propellant. With a propellant loading of 2 tonnes (Mono-Methyl Hydrazine as fuel + Mixed Oxides of Nitrogen as oxidiser), each of these engines generates a maximum thrust of 7.4 kN. Engine is gimbaled (±3°) for pitch, yaw & roll control and for control during the coast phase uses on-off RCS. PSLV-C4 used a new lightweight carbon composite payload adapter to enable a greater GTO payload capability.
PSLV is developed with a group of wide-range control units.
| Stage 1 | Stage 2 | Stage 3 | Stage 4 | |
|---|---|---|---|---|
| Pitch | SITVC | Engine Gimbal | Flex Nozzle | Engine Gimbal |
| Yaw | SITVC | Engine Gimbal | Flex Nozzle | Engine Gimbal |
| Roll | RCT and SITVC in 2 PSOMs | HRCM Hot Gas Reaction Control Motor | PS4 RCS | PS4 RCS |
Read more about this topic: Polar Satellite Launch Vehicle
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