Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle (PSLV) is an expendable medium-lift launch vehicle designed and operated by the Indian Space Research Organisation (ISRO). It was developed to allow India to launch its Indian Remote Sensing (IRS) satellites into Sun-synchronous orbits, a service that was, until the advent of the PSLV in 1993, only commercially available from Russia. PSLV can also launch small size satellites into Geostationary Transfer Orbit (GTO). Some notable payloads launched by PSLV include India's first lunar probe Chandrayaan-1, India's first interplanetary mission, Mars Orbiter Mission (Mangalyaan), India's first space observatory, Astrosat and India's first Solar mission, Aditya-L1. PSLV has gained credibility as a leading provider of rideshare services for small satellites, owing to its numerous multi-satellite deployment campaigns with auxiliary payloads, usually ride-sharing along with an Indian primary payload. As of June 2022, PSLV has launched 345 foreign satellites from 36 countries. Most notable among these was the launch of PSLV-C37 on 15 February 2017, successfully deploying 104 satellites in Sun-synchronous orbit, tripling the previous record held by Russia for the highest number of satellites sent to space on a single launch, until 24 January 2021, when SpaceX launched the Transporter-1 mission on a Falcon 9 rocket carrying 143 satellites into orbit. Payloads can be integrated in tandem configuration employing a Dual Launch Adapter. Smaller payloads are also placed on equipment deck and customized payload adapters. Development Studies by the PSLV Planning group under S Srinivasan to develop a vehicle capable of delivering a 600 kg payload to a 550 km sun-synchronous orbit from SHAR began in 1978. Among 35 proposed configurations, four were picked; by November 1980, a vehicle configuration with two strap-ons on a core booster (S80) with 80 tonne solid propellant loading each, a liquid stage with 30 tonne propellant load (L30), and an upper stage called the Perigee-Apogee System (PAS) was being considered. By 1981, confidence grew in remote sensing spacecraft development with the launch of Bhaskara-1, and the PSLV project objectives were upgraded to have the vehicle deliver a 1000 kg payload into a 900 km SSO. As technology transfer of Viking rocket engine firmed up, a new lighter configuration with the inclusion of a liquid powered stage was selected. Funding was approved in July 1982 for the finalized design, employing a single large S125 solid core as first stage with six 9 tonne strap-ons (S9) derived from the SLV-3 first stage, liquid fueled second stage (L33), and two solid upper stages (S7 and S2.) This configuration needed further improvement to meet the orbital injection accuracy requirements of IRS satellites, and hence, the solid terminal stage (S2) was replaced with a pressure fed liquid fueled stage (L1.8 or LUS) powered by twin engines derived from roll control engines of the first stage. Apart from increasing precision, liquid upper stage also absorbed any deviation in performance of solid third stage. The final configuration of PSLV-D1 to fly in 1993 was (6 × S9 + S125) + L37.5 + S7 + L2. The inertial navigation