The Polar Satellite Launch Vehicle (PSLV) is an expendable medium-lift launch vehicle, a type of concept and technology developed and operated by the Indian Space Research Organisation (ISRO). Its development began in the early 1990s with the objective of creating a reliable and cost-effective launch vehicle for India's growing space program. The PSLV was specifically designed to solve the problem of launching India's Indian Remote Sensing (IRS) satellites into Sun-synchronous orbits (SSO), a service that was previously only commercially available from Russia. The first flight, PSLV-D1, took place on September 20, 1993, and its first successful launch was in October 1994.
The PSLV is India's third-generation launch vehicle and the first to be equipped with liquid stages, earning it the title of the "workhorse of ISRO". It operates through a four-stage mechanism, alternating between solid and liquid propulsion systems. The First Stage (PS1) and Third Stage (PS3) are solid-fueled, using Hydroxyl-Terminated Polybutadiene (HTPB) propellant. The Second Stage (PS2) is liquid-fueled, powered by the Vikas engine which uses Unsymmetrical Dimethylhydrazine (UDMH) and Nitrogen Tetroxide (N₂O₄). The Fourth Stage (PS4) is also liquid-fueled, using two engines that burn Monomethylhydrazine (MMH) and Mixed Oxides of Nitrogen (MON) for precise orbital insertion.
The PSLV connects directly to ISRO's major missions, having launched India's first lunar probe, Chandrayaan-1 in 2008, the Mars Orbiter Mission (Mangalyaan) in 2013, and the solar mission Aditya-L1. It is also related to the Geosynchronous Satellite Launch Vehicle (GSLV), which is primarily used for heavier communication satellites into Geostationary Transfer Orbit (GTO). The PSLV has evolved into multiple variants to cater to different payload requirements, including the PSLV-CA (Core Alone) without strap-on motors, the PSLV-XL with six extended strap-on motors, and the more recent PSLV-DL (two strap-ons) and PSLV-QL (four strap-ons) variants, with the PSLV-DL variant first flying on January 24, 2019. The core four-stage design and the alternating solid-liquid propulsion have remained the same, but the addition of new variants like PSLV-QL and PSLV-DL has amended the vehicle's configuration options.