maraging steel. The booster develops a maximum thrust of about 4,628 kilo Newtons (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 tonne of HTPB based propellant and produces 662 kN thrust.

The second stage employs the Vikas engine which carries 40 tonne 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 composite. 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 and Mixed Oxides of Nitrogen), each of these engines generates a maximum thrust of 7.4 kN.

The 3.2 m diameter metallic bulbous payload fairing of PSLV protects the spacecraft during the atmospheric regime of the flight.

PSLV flight control system includes : a) First stage — Secondary Injection Thrust Vector Control (SITVC) for pitch and yaw, liquid propellant thrusters for roll with SITVC in two strap-on motors for roll control augmentation, b) Second stage — Engine gimbal for pitch and yaw and, hot gas reaction

PSLV-C4 Salient Features