The Polar Satellite Launch Vehicle (PSLV) is a medium capacity expendable launch vehicle, first introduced in 1993. It derived much of it's design architecture from it's predecessor, the ASLV. The development of PSLV necessitated many firsts for the then nascent Indian Space Program like Liquid propulsion and large solid boosters.
PSLV performance was progressively improved during the 1990s. The operational "C" version, first flown in 1997, stands 44.4 meters tall and weighs 295 metric tons at liftoff. It consists of four stages that use solid and liquid propellants alternately.
PSLV's 12.5 x 2.8 m PS-2 (L40) second stage is powered by a 73.9 ton-thrust Viking 4 engine that burns unsymmetrical dimethyl hydrazine (UDMH) fuel and nitrogen tetroxide (N2O4) oxidizer for 162 seconds. Viking 4, called "Vikas" by ISRO, was originally built by Europe's SEP for the Ariane 1 launch vehicle.
The third stage is another 2.8 meter diameter solid motor. It burns 7.6 tons of propellant for 109 seconds, producing 33.5 tons of thrust.
The fourth and final stage is a twin-engine liquid propulsion system that is housed within the payload fairing below the satellite. It burns 2.5 tons of mono-methyl hydrazine (MMH) fuel and nitrogen tetroxide (N2O4) oxidizer. The 1.43 ton thrust stage can burn for up to 420 seconds.
The vehicle is controlled by a strap-down inertial navigation/guidance system housed in a vehicle equipment bay that is mounted on top of the fourth stage. An 8.3 meter tall, 3.2 meter diameter payload fairing protects the payload during ascent through the atmosphere.
The original PSLV/GSLV launch complex was replaced in 2005 with a new, mobile launch facility. PSLV-C6 was the first rocket to use the pad. Whereas the original pad featured a fixed launch stand and a 75 meter tall mobile service tower, the new "second launch pad" uses rail-mobile launch stands that allow vehicles to be stacked in a vertical integration building located some distance from the launch pad itself.
The January 10, 2007 PSLV-C7 mission included the first use of a PSLV dual launch adapter, which deployed both Cartosat 2 and the SRE 1 demonstration recovery capsule and carried a small microsatellite.
The PSLV-CA (Core Alone) model premiered on April 23, 2007. The CA model did not include the six strap-on boosters used by the PSLV-C variant. Two small roll control modules and two first stage motor control injection tanks were still attached to the side of the first stage. About 400 kg of propellant was offloaded from the fourth stage compared to PSLV-C.
