Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle is an expendable medium-lift launch vehicle designed and operated by the Indian Space Research Organisation. 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, commercially available only 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 and India's first space observatory, Astrosat.
PSLV has gained credence as a leading provider of rideshare services for small satellites, due its numerous multi-satellite deployment campaigns with auxiliary payloads usually ride sharing along an Indian primary payload. As of December 2019, PSLV has launched 319 foreign satellites from 33 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.
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 to develop a vehicle capable of delivering 600 kg payload to 550 km Sun-synchronous orbit from SHAR began in 1978. Among 35 proposed configurations, four were picked and 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 Perigee-Apogee System was being considered.By 1981, confidence grew in remote sensing spacecraft development with launch of Bhaskara-1 and the PSLV project objectives were upgraded to have vehicle deliver 1000 kg payload in 900 km SSO. As technology transfer of Viking rocket engine firmed up, a new lighter configuration shifting away from relying on three large solid boosters was proposed by team led by APJ Abdul Kalam and eventually selected. Funding was approved in July 1982 for finalized design employing a single large S125 solid core as first stage with six 9 tonne strap-ons derived from SLV-3 first stage, liquid fueled second stage 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 solid terminal stage was replaced with a pressure fed liquid fueled stage powered by twin engines derived from roll control engines of first stage. Apart from increasing precision, liquid upper stage also absorbed any deviation in performance of solid third stage. 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 stages for the second and fourth stages of PSLV as well as the Reaction control systems are developed by the Liquid Propulsion Systems Centre at Mahendragiri near Tirunelveli, Tamil Nadu. The solid propellant motors are processed at Satish Dhawan Space Centre at Sriharikota, Andhra Pradesh which also carries out launch operations.
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. By Nov 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.
ISRO is planning to privatise the operations of PSLV and will work through a joint venture with private industries. The integration and launch will be managed an industrial consortium through Antrix Corporation.
In June 2018, the Union Cabinet approved for 30 operational flights of the PSLV scheduled to take place between 2019 and 2024.
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 tonnes 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 some quantity of water in a toroidal tank at its bottom. Water spray is used to cool hot gases from Vikas' gas generator before entering turbopump.
Third stage (PS3)
The third stage uses of hydroxyl-terminated polybutadiene-based solid propellant and produces a maximum thrust of. It has a Kevlar-polyamide fibre case and a submerged nozzle equipped with a flex-bearing-seal gimbaled nozzle thrust vector engine for pitch & yaw control. Roll control is provided by the fourth stage reaction control system during thrust phase as well as during combined-coasting phase.Fourth stage (PS4)
The fourth stage is powered by regeneratively cooled twin engines, burning monomethylhydrazine and mixed oxides of nitrogen. Each engine generates thrust and is gimbaled to provide pitch, yaw & roll control during powered flight. Coast phase attitude control is provided by RCS. The stage carries up to of propellant in the PSLV and PSLV-XL and in the PSLV-CA.PS4 stage as orbital platform
PS4 has carried hosted payloads like AAM on PSLV-C8, Rubin 9.1/ Rubin 9.2 on PSLV-C14 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 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 spacecrafts.
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. Three payloads hosted on PS4-OP were, Advanced Retarding Potential Analyzer for Ionospheric Studies by IIST, experimental AIS payload by ISRO and AISAT by Satellize.
Payload fairing
Payload fairing of PSLV, also referred as its 'Heatshield' weighs 1,182 kg and has 3.2 meter diameter. 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 horizontal and vertical separation mechanisms.| Stage 1 | Stage 2 | Stage 3 | Stage 4 | |
| Pitch | SITVC | Engine Gimbal | Nozzle Flex | Engine Gimbal |
| Yaw | SITVC | Engine Gimbal | Nozzle Flex | Engine Gimbal |
| Roll | RCT and SITVC in 2 PSOMs | HRCM Hot Gas Reaction Control Motor | PS4 RCS | PS4 RCS |
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 without strap-on motors, and the version, with six extended length 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 (retired)
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 with 9 tonne propellant loading. It had 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. The fourth stage of the CA variant has less propellant when compared to its standard version. It currently has capability to launch to Sun synchronous orbit.PSLV-XL
PSLV-XL is the upgraded version of Polar Satellite Launch Vehicle in its standard configuration boosted by more powerful, stretched strap-on boosters with 12 tonne propellant load. Weighing at lift-off, the vehicle uses larger strap-on motors to achieve higher payload capability. On 29 December 2005, ISRO successfully tested the improved version of 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 SSO.PSLV-DL
PSLV-DL variant has only two strap-on boosters with 12 tonne propellant load on them. PSLV-C44 on 24 January 2019 was the first flight to use PSLV-DL variant of Polar Satellite Launch Vehicle.PSLV-QL
PSLV-QL variant has four ground-lit strap-on boosters, each with 12 tonnes of propellant. PSLV-C45 on 1 April 2019 was the first flight of PSLV-QL.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 history
| Variant | Launches | Successes | Failures | Partial failures |
| PSLV-G | 12 | 10 | 1 | 1 |
| PSLV-CA | 14 | 14 | 0 | 0 |
| PSLV-XL | 22 | 21 | 1 | 0 |
| PSLV-DL | 1 | 1 | 0 | 0 |
| PSLV-QL | 2 | 2 | 0 | 0 |
| Total as of 2019 | 50 | 47 | 2 | 1 |