The Indian Space Research Organisation’s (ISRO) Polar Satellite Launch Vehicle (PSLV), which costs nearly ₹200 crore, is a third-generation rocket. It is the first Indian launch vehicle to be equipped with liquid stages. PSLV has three variants: PSLV-Core alone (PSLV-CA) without the solid strap-on motors; a PSLV with six solid strap-on boosters; and PSLV-XL, the top model, with six extended solid strap-on boosters.

The launch capability of the PSLV with these configurations varies from 1,000-1,750 kg.

The biggest advantage of PSLV is that it is capable of placing multiple payloads into orbit with multi-payload adaptors used in the payload fairing. Multiple engine restarts to achieve multiple orbits in the same mission depending on the mission requirements, have also been demonstrated successfully for the PSLV.

Read: ISRO workhorse PSLV set to make history with 50th launch on December 11

PSLV has also been used to launch various satellites into geosynchronous and geostationary orbits, such as satellites from the IRNSS constellation.

A satellite in a geosynchronous orbit has an orbital period matching that of the earth. It synchronises with the movement of the earth, which takes 23 hours, 56 minutes and 4.09 seconds to rotate on its axis. As such, to a ground observer, these satellites appear to be at a fixed point above the earth. They are used to monitor the weather and for communications, as well as for surveillance.

Geostationary orbits are also geosynchronous orbits. The key difference is that these satellites are on the same plane as the equator, 35,785 km above the Earth, unlike geosynchronous satellites, which can have any inclination.

Technical Specifications

Payload to Sun-Synchronous Polar Orbits (SSPO): 1,750 kg

Payload to Sub geosynchronous transfer orbit (GTO): 1,425 kg

Stages of journey

There are four stages in PSLV’s journey from lift-off to placing satellites into orbit. In the first stage (PS1), the PSLV uses the S139 solid rocket motor, which is augmented by six solid strap-on boosters. It provides the launcher the high thrust that is required for lift-off. It uses the S139 solid rocket booster, which contains nearly 138 tonnes of Hydroxyl Terminated Polybutadiene (HTPB) based propellant.

In the second stage (PS2), the launch vehicle uses an Earth storable liquid rocket engine known as Vikas, which was developed by a Liquid Propulsion Systems Centre in the early 90s.

The third Stage (PS3) involves a solid rocket motor that provides the upper stages high thrust after the atmospheric phase of the launch. This is the penultimate stage of the PSLV, using a solid rocket for propulsion.

The final stage (PS4) is the uppermost stage of the PSLV, and comprises of two Earth storable liquid engines. This stage is responsible for the correct injection of PSLV's payloads into their respective desired orbits.

Strap-on booster

While the PSLV-G uses six HTPB based solid strap-on motors of 9 tonnes each and PSLV-XL uses 6 extended strap-ons of 12 tonnes each, the PSLV-CA (core alone version) does not use any strap-on motors.

Strap-on motors

PSLV uses six solid rocket strap-on motors to augment the thrust provided by the first stage in its PSLV-G and PSLV-XL variants. However, strap-ons are not used in the core alone version (PSLV-CA).

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