Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle is an expendable medium-lift launch vehicle designed and operated by ISRO. It was developed to allow India to launch its Indian Remote Sensing 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.
Some notable payloads launched by PSLV include India's first lunar probe Chandrayaan-1, India's first interplanetary mission, Mars Orbiter Mission, 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 with 80 tonne solid propellant loading each, a liquid stage with 30 tonne propellant load, and an upper stage called the Perigee-Apogee System 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 derived from the SLV-3 first stage, liquid fueled second stage, and two solid upper stages This configuration needed further improvement to meet the orbital injection accuracy requirements of IRS satellites, and hence, the solid terminal stage was replaced with a pressure fed liquid fueled stage 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 + L37.5 + S7 + L2.
The inertial navigation systems are developed by ISRO Inertial Systems Unit at Thiruvananthapuram. The liquid propulsion for the second and fourth stages of the PSLV as well as the Reaction control systems are developed by the Liquid Propulsion Systems Centre at Valiamala near Thiruvananthapuram, kerala. The solid propellant motors are processed at Satish Dhawan Space Centre at Sriharikota, Andhra Pradesh, which also carries out launch operations. The aerodynamic characterization research was conducted at the National Aerospace Laboratories' 1.2m Trisonic Wind Tunnel Facility.
The PSLV was first launched on 20 September 1993. The first and second stages performed as expected, but an attitude control problem led to the collision of the second and third stages at separation, and the payload failed to reach orbit. 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.
PSLV continues to support Indian and foreign satellite launches especially for low Earth orbit satellites. It has undergone several improvements with each subsequent version, especially those involving thrust, efficiency as well as weight. In November 2013, it was used to launch the Mars Orbiter Mission, India's first interplanetary probe.
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 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 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 modules with small bi-propellant 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 propellant and produce and thrust respectively. Two strap-on boosters are equipped with SITVC for additional attitude control. The PSLV-CA uses no strap-on boosters.First stage separation is aided by four pairs of retro-rockets installed on inter-stage. During staging, these eight rockets help push away the spent stage away from second stage.
Second stage (PS2)
The second stage is powered by a single Vikas engine and carries of Earth store-able liquid propellantunsymmetrical dimethylhydrazine as fuel and nitrogen tetroxide as oxidiser in two tanks separated by a common bulkhead. It generates a maximum thrust of. The engine is gimbaled in two planes to provide pitch and yaw control by two actuators, while roll control is provided by a Hot gas Reaction Control Motor that ejects hot gases diverted from gas generator of Vikas engine.On inter-stage 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.
Second stage also carries water in a toroidal tank at its bottom. 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 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 and mixed oxides of nitrogen. Each pressure fed engine generates thrust and is gimbaled 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.