Polar Satellite Launch Vehicle

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 PSLV was first launched on 20 September 1993. After this initial setback, the PSLV successfully completed its second mission in 1994. The fourth launch of PSLV suffered a partial failure in 1997, leaving its payload in a lower than planned orbit. In November 2014, the PSLV had launched 34 times with no further failures. (Although launch 41: August 2017 PSLV-C39 was unsuccessful. In June 2018, the Union Cabinet approved for 30 operational flights of the PSLV scheduled to take place between 2019 and 2024. ISRO is working towards handing over the production and operation of PSLV to private industry through a joint venture. On 16 August 2019, NewSpace India Limited issued an invitation to tender for manufacturing PSLV entirely by private industries. On 5 September 2022, NewSpace India Limited signed a contract with Hindustan Aeronautics Limited and Larsen & Toubro led conglomerate for the production of five PSLV-XL launch vehicles after they won competitive bidding. Under this contract, they have to deliver their first PSLV-XL within 24 months and the remaining four vehicles every six months. == Vehicle description ==

The PSLV has four stages, using solid and liquid propulsion systems alternately. First stage (PS1) The first stage, one of the largest solid rocket boosters in the world, carries of hydroxyl-terminated polybutadiene-bound (HTPB) propellant and develops a maximum thrust of about . The diameter motor case is made of maraging steel and has an empty mass of . Pitch and yaw control during first stage flight is provided by the Secondary Injection Thrust Vector Control (SITVC) System, which injects an aqueous solution of strontium perchlorate into the S139 exhaust divergent from a ring of 24 injection ports to produce asymmetric thrust. The solution is stored in two cylindrical aluminium tanks strapped to the core solid rocket motor and pressurised with nitrogen. Underneath these two SITVC tanks, Roll Control Thruster (RCT) modules with small bi-propellant (MMH/MON) liquid engine are also attached. On the PSLV-G and PSLV-XL, first stage thrust is augmented by six strap-on solid boosters. Four boosters are ground-lit and the remaining two ignite 25 seconds after launch. The solid boosters carry or (for PSLV-XL configuration) propellant and produce and thrust respectively. Two strap-on boosters are equipped with SITVC for additional attitude control. Second stage (PS2) The second stage is powered by a single Vikas engine and carries of Earth store-able liquid propellantunsymmetrical dimethylhydrazine (UDMH) as fuel and nitrogen tetroxide (N2O4) as oxidiser in two tanks separated by a common bulkhead. On inter-stage (1/2U) of PS2, there are two pairs of ullage rockets to maintain positive acceleration during PS1/PS2 staging and also two pairs of retro-rockets to help push away spent stage during PS2/PS3 staging. Water spray is used to cool hot gases from Vikas' gas generator to about 600 °C before entering turbopump. Propellant and water tanks of second stage are pressurized by Helium. Third stage (PS3) The third stage uses of HTPB solid propellant and produces a maximum thrust of . Its burn duration is 126.7 seconds. It has a Kevlar-polyamide fibre case and a submerged nozzle equipped with a flex-bearing-seal gimbaled nozzle with ±2° thrust vector for pitch and yaw control. Roll control is provided by the fourth stage reaction control system (RCS) during thrust phase as well as during combined-coasting phase under which burnt-out PS3 remains attached to PS4. Fourth stage (PS4) The fourth stage is powered by regeneratively cooled twin engines, burning monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON). Each pressure fed engine generates thrust and is gimbaled (±3°) to provide pitch, yaw and roll control during powered flight. Coast phase attitude control is provided by six 50N RCS thrusters. The stage is pressurized by helium and carries to of propellant depending on the mission requirements. PS4 has three variants L1.6, L2.0 and L2.5 based on propellant tank capacity. On PSLV-C29/TeLEOS-1 mission, the fourth stage demonstrated re-ignition capability for the first time which was used in many subsequent flights to deploy payloads in multiple orbits on a single campaign. As a space debris mitigation measure, PSLV fourth stage gets passivated by venting pressurant and propellant vapour after achieving main mission objectives. Such passivation prevents any unintentional fragmentation or explosion due to stored internal energy. The niobium alloy nozzle used on twin engines of fourth stage is expected to be replaced by lighter, silicon carbide coated carbon–carbon nozzle divergent. The new nozzle was hot tested at facilities of IPRC, Mahendragiri in March and April 2024. This substitution should increase payload capacity of PSLV by . ISRO also replaced imported Columbium materials in the engine nozzle divergent with Stellite, which resulted in cost savings of 90%. The newly modified engines were tested at IPRC in April 2025. ISRO successfully completed 665-second hot test of 3D printed PS4 engine, produced by Wipro 3D through selective laser melting. A total of 19 weld joints were eliminated through this process while engine's 14 components were reduced to one piece. It saved 60% of the production time and drastically decreased the amount of raw materials used per engine, from 565 kg to 13.7 kg of metal powder. PS4 stage as orbital platform PS4 has carried hosted payloads like AAM on PSLV-C8, and mRESINS on PSLV-C21. But now, PS4 is being augmented to serve as a long duration orbital platform after completion of primary mission. PS4 Orbital Platform (PS4-OP) will have its own power supply, telemetry package, data storage and attitude control for hosted payloads. On PSLV-C37 and PSLV-C38 campaigns, as a demonstration PS4 was kept operational and monitored for over ten orbits after delivering spacecraft. PSLV-C44 was the first campaign where PS4 functioned as independent orbital platform for short duration as there was no on-board power generation capacity. It carried KalamSAT-V2 as a fixed payload, a 1U CubeSat by Space Kidz India based on Interorbital Systems kit. On PSLV-C45 campaign, the fourth stage had its own power generation capability as it was augmented with an array of fixed solar cells around PS4 propellant tank. The three payloads hosted on PS4-OP were the Advanced Retarding Potential Analyzer for Ionospheric Studies (ARIS 101F) by IIST, an experimental AIS payload by ISRO, and AISAT by Satellize. To function as orbital platform, fourth stage was put in spin-stabilized mode using its RCS thrusters. On the PSLV-C53 campaign, the PS4-OP is referred to as the PSLV Orbital Experimental Module (POEM), and it hosted six payloads. POEM was the first PSLV fourth stage based orbital platform to be actively stabilised using Helium based cold gas thrusters after the primary mission and stage passivization. PS4 on RLV-OREX The Reusable Launch Vehicle Technology Demonstration program is an prototype spaceplane project currently being processed by ISRO. It is planned to use a GSLV, modified by replacing its Cryogenic Upper Stage(CUS) with the PS-4 as the RLV would not required the excess thrust created by the CUS. Payload fairing Payload fairing of PSLV, also referred as its "Heatshield" consists of a conical upper section with spherical nose-cap, a cylindrical middle section and a lower boat-tail section. Weighing , it has 3.2 meter diameter and 8.3 meter height. It has Isogrid construction and is made out of 7075 aluminum alloy with a 3 mm thick steel nose-cap. The two halves of fairing are separated using a pyrotechnic device based jettisoning system consisting of horizontal and lateral separation mechanisms. To protect the spacecraft from damage due to excessive acoustic loads during launch, the heatshield interior is lined with acoustic blankets. Integration gallery File:PSLV-C11 Strapon01.jpg|PSLV-C11 strap-on File:PSLV-C44 Integrated upto First Stage inside Mobile Service Tower.jpg|PSLV-C44 first stage inside Mobile Service Tower File:PSLV-C55, TeLEOS-2 - Igniter of first stage being integrated with head end segment.webp|First stage Igniter being integrated onto the rocket File:PSLVC62 ullage motor.jpg|PSLV Ullage motors File:PSLVC62 interstage.webp|PSLV First-Second interstage File:PSLV C50 second stage with Vikas engine.jpg|Vikas engine and second stage File:PSLV C45 EMISAT campaign 09.jpg|Third and fourth stages of PSLV-C45 File:Payload Encapsulation of PSLV - C62.webp|Payload fairing integration File:PSLVC62 PSLV rollout.webp|Rollout prior to launch == Variants ==

ISRO has envisaged a number of variants of PSLV to cater to different mission requirements. There are currently two operational versions of the PSLV — the core-alone (PSLV-CA) without strap-on motors, and the (PSLV-XL) version, with six extended length (XL) strap-on motors carrying 12 tonnes of HTPB based propellant each. These configurations provide wide variations in payload capabilities up to in LEO and in sun-synchronous orbit. PSLV-G The standard or "Generic" version of the PSLV, PSLV-G had four stages using solid and liquid propulsion systems alternately and six strap-on motors (PSOM or S9) with 9 tonne propellant loading. It had the capability to launch to into sun-synchronous orbit. PSLV-C35 was the last operational launch of PSLV-G before its discontinuation. PSLV-CA The PSLV-CA, CA meaning "Core Alone", model premiered on 23 April 2007. The CA model does not include the six strap-on boosters used by the PSLV standard variant but two SITVC tanks with Roll Control Thruster modules are still attached to the side of the first stage with addition of two cylindrical aerodynamic stabilizers. PSLV-XL PSLV-XL is the upgraded version of Polar Satellite Launch Vehicle in its standard configuration boosted by more powerful, stretched six strap-on boosters with 12 tonne propellant load. On 29 December 2005, ISRO successfully tested an improved version of the strap-on booster for the PSLV. The first use of PSLV-XL was the launch of Chandrayaan-1 by PSLV-C11. The payload capability for this variant is to Sun-synchronous orbit. It is capable of launching to Sun-synchronous orbit. It has the capacity to launch to Sun-synchronous orbit. PSLV-3S (concept) PSLV-3S was conceived as a three-staged version of PSLV with its six strap-on boosters and second liquid stage removed. The total lift-off mass of PSLV-3S was expected to be 175 tonnes with capacity to place 500 kg in 550 km low Earth orbit. == Launch profile ==

PSLV - XL: • The PS1 ignites at T+0 providing 4846kN of thrust. • Within T+1, 4 out of the 6 boosters ignite on ground, each producing 703 kN of thrust. 7658kN of total thrust is produced by the combined propulsion of the PSOMs and the PS1. • At around T+23/26, the remaining 2 unlit boosters are air-lit bringing the rocket at its maximum thrust capacity. • At T+1:10, the first 4 ground-lit PSOMs have depleted its propellant and now separates and falls down to the ocean. The remaining 2 PSOMs and the PS1 continue to burn. • At T+1:35, the remaining 2 PSOMs complete its 70 seconds burn and separate, leaving the rocket in a Core Alone configuration. • At T+1:50, the PS1 has completed its 110-second burn and it separates and the Vikas Engine inside the PS2 ignites. • The second stage burns for around 130 seconds and around T+4 minutes, the second stages shuts off and separates. • The third stage, which is a solid rocket booster, and burns 80 seconds and then coasts for the remainder of time and around T+8/10 minutes, it separates and the 4th stage ignites to give the rocket a final push into the orbit. • This 4th stage burn is highly variable and depends on the mass and number of payloads and is usually around 500 seconds long. The 4th stage may shut off around T+16/18 minutes followed by the Payload Deployment. == Launch statistics ==

Launch system status Decade-wise summary of PSLV launches == Gallery ==

File:PSLV - C54 Launch By SDSC , SHAR.webp|PSLV - C54 Liffed off from Satish Dhawan Space Center's, First Launch Pad. File:C533.webp|PSLV C53 Clears Second Launch Pad of Satish Dhawan Space Centre, Shriharikota File:PSLV-C52, EOS-04 (aka RISAT-1A) - Liftoff from First Launch Pad of Satish Dhawan Space Centre, Sriharikota 008.jpg|PSLV C52 lifting off from First Launch Pad File:PSLV-C49, EOS-01(aka RISAT-2BR2) launch from First Launch Pad 001.jpg|PSLV-C49 lift off File:PSLV C45 EMISAT campaign 23.jpg|PSLV C45 ignition File:PSLV C45 EMISAT campaign 12.jpg|Top view of PSLV C45 File:PSLV C48 RISAT-2BR1 lift-off from First Launch Pad 007.jpg|PSLV C48 RISAT-2BR1 lift-off from First Launch Pad File:PSLV-C11 launch2.jpg|PSLV C11 lift off File:PSLV-C44 Microsat-R launch from First Launch Pad SDSC SHAR Sriharikota 06.jpg|PSLV C44 lift off File:PSLV-C55, TeLEOS-2 - Launch vehicle on First Launch Pad (FLP) with Mobile Servicing Tower (MST) retracted at SDSC-SHAR, Sriharikota 01.webp|Integrated PSLV rocket File:PSLV-C50, CMS-01- Midflight vapor cone 005.jpg|PSLV in flight File:PSLV-C53, DS-EO - Mid-flight with a visible vapor cone or shock collar formed around payload fairing.jpg|PSLV Mid-flight with a visible vapor cone or shock collar formed around payload fairing == See also ==