Polar Satellite Launch Vehicle (PSLV)

The Polar Satellite Launch Vehicle (PSLV) is a rocket made by the Indian Space Research Organisation (ISRO). Its main job is to carry satellites weighing up to about one and a half tonnes into orbits a few hundred kilometres above the Earth, especially orbits that pass over the North and South Poles. Because it has flown so many missions so reliably, it is often called ISRO's "workhorse". TRISHNA, Chandrayaan-1, the Mars Orbiter Mission and Aditya-L1 all went to space on a PSLV.

Why was the PSLV needed?

In the 1980s, India wanted its own remote sensing satellites: satellites that take pictures of the Earth to study crops, forests, water and cities. These satellites work best in a polar, sun-synchronous orbit. India's earlier small rockets, the SLV and ASLV, could only carry about 40 to 150 kg to low orbits. So India had to pay foreign agencies to launch its satellites.

For example, the first Indian Remote Sensing satellite, IRS-1A (1988), went up on a Soviet rocket. A bigger Indian rocket was needed to make India self-reliant.

Where did it come from?

• ISRO started developing the PSLV in the 1980s.
• The first flight, PSLV-D1 on 20 September 1993, failed because of a software error in the guidance system, and its satellite (IRS-1E) was lost.
• The first successful flight, PSLV-D2, came on 15 October 1994. It placed the IRS-P2 satellite in a polar sun-synchronous orbit.
• Since then it has flown more than 60 times from the Satish Dhawan Space Centre, Sriharikota (Andhra Pradesh), with only a handful of failures.

How does a four-stage rocket work?

A rocket is like a relay race team. Each runner (stage) runs as hard as it can, then hands over and drops away. Throwing away empty fuel tanks makes the rest of the rocket lighter, so it can go faster. PSLV has four stages, and they alternate between solid and liquid fuel:

1. First stage (PS1): a big solid motor (the S139). Many versions also have extra solid boosters strapped to its sides, called strap-on motors.
2. Second stage (PS2): a liquid stage powered by the Vikas engine.
3. Third stage (PS3): a solid motor.
4. Fourth stage (PS4): a liquid stage with two engines that can be switched off and restarted. This lets PSLV drop different satellites into slightly different orbits on one flight.

Solid fuel is like a firecracker: once lit, it burns until it is finished. It gives huge push at lift-off. Liquid fuel is like a gas stove: it can be controlled, and sometimes switched off and on. Using both gives power and control.

The key facts and versions

PSLV stands about 44 metres tall. Its versions differ only in the number of strap-on boosters:

• PSLV-CA ("Core Alone"): no strap-ons. Lightest version.
• PSLV-DL: 2 strap-ons.
• PSLV-QL: 4 strap-ons.
• PSLV-XL: 6 larger strap-ons. The most powerful version, able to put about 1,750 kg into a sun-synchronous orbit of about 600 km. It was first used for Chandrayaan-1 in 2008.

Famous PSLV missions

• Chandrayaan-1 (October 2008): India's first mission to the Moon. It helped find evidence of water molecules on the Moon.
• Mars Orbiter Mission / Mangalyaan (5 November 2013): made India the first country to reach Mars orbit on its first attempt.
• PSLV-C37 (15 February 2017): launched 104 satellites in one flight, a world record at that time. Most of them were small foreign satellites.
• Aditya-L1 (2 September 2023, PSLV-C57): India's first mission to study the Sun from the Lagrange point L1.
• Megha-Tropiques (2011) and SARAL (2013): the two earlier Indo-French satellites.

PS4 as a space lab (POEM)

After the satellites are released, the empty fourth stage used to become space junk. ISRO now reuses it as a small floating platform, called POEM (PSLV Orbital Experimental Module), which can carry small experiments from start-ups and universities for some weeks.

Commercial launches and industry

PSLV has launched hundreds of foreign satellites for paying customers. This is handled by ISRO's commercial companies, such as NewSpace India Limited (NSIL). In 2022, NSIL gave a contract to a consortium of Hindustan Aeronautics Limited (HAL) and Larsen & Toubro (L&T) to build five PSLV-XL rockets. This is the first time an Indian company group will build a whole PSLV, so that ISRO can focus on research and new rockets.

Commonly confused concepts

• PSLV vs GSLV: PSLV mainly carries satellites to low, polar orbits (a few hundred km). The GSLV (Geosynchronous Satellite Launch Vehicle) uses a cryogenic upper stage (super-cold liquid hydrogen and oxygen) to send heavier communication satellites towards the geostationary orbit about 36,000 km high. LVM3 (formerly GSLV Mk III) is the heaviest Indian rocket.
• "Polar" does not mean polar only: PSLV can also put satellites in other orbits, and has even sent missions to the Moon, Mars and the Sun-Earth L1 point.
• SSLV: the Small Satellite Launch Vehicle is a separate, smaller three-stage rocket for satellites up to about 500 kg, designed to be cheap and quick to prepare.
• Polar orbit vs sun-synchronous orbit: a polar orbit passes over (or near) the poles. A sun-synchronous orbit is a special near-polar orbit in which the satellite crosses any place at the same local time every day, so pictures taken on different days have similar sunlight.

Issues, criticism and the way forward

• Recent failures: PSLV had a long run of successes, but two flights failed in a row: PSLV-C61 (May 2025), carrying the radar satellite EOS-09, and PSLV-C62 (January 2026), which lost 16 satellites. Both problems were traced to the third stage. ISRO set up failure analysis committees, but the full reports have not been made public. Experts say openness about failures builds trust with foreign customers.
• Competition: Cheap reusable rockets from private companies abroad have lowered launch prices. A rocket that is thrown away after each flight, like PSLV, must compete on reliability and price.
• Way forward: Handing PSLV production to industry (HAL-L&T), using SSLV for small satellites, and developing reusable rockets are the steps ISRO has chosen to stay competitive.

Concepts to Know

• Orbit: The curved path a satellite follows around the Earth, like a ball tied to a string being swung around.
• Payload: The useful cargo a rocket carries, usually satellites. The rocket itself is just the delivery truck.
• Remote sensing: Studying the Earth from far away, usually by taking pictures from satellites in different kinds of light.
• Sun-synchronous orbit (SSO): A near-polar orbit in which a satellite passes over any given place at the same local time every day. This keeps the lighting similar in all pictures.
• Strap-on motor: An extra rocket attached to the side of the main rocket to give more push at lift-off. It falls away after its fuel is used up.
• Cryogenic engine: An engine that uses fuels cooled to extremely low temperatures (liquid hydrogen at about minus 253°C). PSLV does not use one; GSLV and LVM3 do.