Vikas Engine: Viking Roots, Hypergolic Fuel and Its Gaganyaan Role
Vikas engine explained: ISRO's storable liquid engine from the 1974 SEP deal, which powers PSLV's second stage, GSLV and the L110 core stage of LVM3.
The Vikas engine is the liquid-fueled rocket engine that has flown on every PSLV, every GSLV and every LVM3, built by ISRO’s Liquid Propulsion Systems Centre (LPSC). It burns a storable, self-igniting pair of propellants, it carries India’s rockets through the middle of their climb, and two of them will lift the first Gaganyaan crew. Its technology came from France under a 1974 agreement, and its name honors Vikram Sarabhai.
Most readers carry one of two wrong ideas about it. The first is that Vikas is a copy of a French engine that India bought. It isn’t; no money changed hands, and India paid in engineering work and hardware. The second is that Vikas is the engine that took India to the Moon on its own. It shares that work with solid boosters and a cryogenic upper stage. This note sorts out who contributed what, where each Vikas flies and what replaces it next.
What is the Vikas engine?
The Vikas engine is an earth-storable liquid engine: its fuel and oxidizer stay liquid at room temperature, so they can sit in a rocket’s tanks for days without the chilling a cryogenic engine needs. ISRO calls it the workhorse of its launchers, and the table below gathers the facts ISRO and LPSC publish.
| Fact | Detail |
|---|---|
| Developer | Liquid Propulsion Systems Centre (LPSC), ISRO |
| Origin | Know-how for France’s Viking engine under a 1974 ISRO-SEP agreement |
| Name | Vikas, Sanskrit for development; also read as VIKram A. Sarabhai |
| Propellants | Nitrogen tetroxide (N2O4) with UDMH or UH25 (UDMH plus 25% hydrazine hydrate), hypergolic |
| Feed system | Turbopump fed, gas generator cycle |
| Thrust | About 800 kN (80 tonnes) nominal; 799 kN on PSLV, 846 kN in the high thrust version on GSLV |
| First flight | PSLV-D1, 20 September 1993, as the second stage (PS2) |
| Flies on | PSLV (PS2), GSLV (GS2 and four L40 strap-ons), LVM3 (twin-engine L110 core stage) |
| Human rating | L110-G Vikas qualified for Gaganyaan with a final 240-second test on 6 April 2023 |
How the Vikas engine works
Vikas is a pump-fed, gas generator cycle engine. Pumps push the propellants into the combustion chamber, and a small side flame, the gas generator, spins the turbine that drives those pumps. Think of it as a car engine that uses a little of its own fuel to run the fuel pump. The cycle is simpler than the staged combustion used in ISRO’s newest engines, and that simplicity is part of why it has lasted.
The more interesting word is hypergolic. Hypergolic propellants ignite the instant they touch each other, with no spark plug or igniter. Nitrogen tetroxide is the oxidizer, the chemical that supplies oxygen. The fuel is unsymmetrical dimethylhydrazine, UDMH. LPSC’s stage data lists the fuel as UH25, a blend of UDMH with 25% hydrazine hydrate. Both names appear in ISRO material, so an aspirant should recognize both.
Why does self-ignition matter? An engine that lights by contact lights reliably, including high in the sky after a lower stage falls away. LPSC’s PSLV data shows exactly that use: the PS2 stage ignites at about 50 km altitude and burns for about 150 seconds, pushing the rest of the rocket and the satellite onward.
The price is toxicity. UDMH and nitrogen tetroxide are hazardous to handle, which is why ISRO describes its future LOX-kerosene engine as non-toxic and non-hazardous. Vikas is reliable and storable. Clean, it is not.
One engine, several ratings
The thrust figure changes with the vehicle, and that trips up almost everyone who memorizes a single number. LPSC and ISRO give these values:
- 720 kN for the GS2 engine on GSLV-D1 in 2001, and 680 kN for each strap-on on that flight;
- 762 kN for each L40 strap-on of today’s GSLV;
- 799 kN for PSLV’s PS2 stage;
- 846 kN for GSLV’s GS2, which uses the higher chamber pressure version;
- 1,692 kN for the two engines of LVM3’s L110 stage together.
The engine family is one design uprated over three decades. The safe answer in any exam is “about 800 kN, or 80 tonnes of thrust,” which is how LPSC itself describes the nominal engine.
Where the Viking deal came from
The Vikas engine began as a trade. In 1974, ISRO signed an agreement with the Société Européenne de Propulsion (SEP), the French firm then developing the Viking engine for the Ariane launcher. A. E. Muthunayagam, LPSC’s founder director, records the terms in his memoir, collected by the Space Museum at the BM Birla Science Centre, Hyderabad:
- no money changed hands;
- SEP transferred technology for pressure transducers and the Viking liquid engine;
- ISRO produced and supplied 7,000 pressure transducers to SEP;
- ISRO spared 100 man-years of its engineers and scientists for Ariane’s development.
About 40 Indian engineers worked inside the Ariane programme, in design reviews, testing and quality checks, and came back with the full drawings. Muthunayagam names S. Nambinarayanan as the leader of that effort. He also records that T. N. Seshan, then Additional Secretary in the Department of Space and later Chief Election Commissioner, signed for ISRO and coined the name Vikas.
The sources don’t agree on every detail, and it helps to know that. A second memoir in the same collection, by N. Narayanamoorthy, describes the deal as one with CNES, France’s space agency, and puts the transducer count at 10,000. The majority account, and the one from the man who founded LPSC, is SEP and 7,000. Treat the transducer number as contested and the 1974 date and the no-cash principle as settled.
From drawings to a flying engine
Having the drawings was the easy half. Narayanamoorthy’s memoir describes the hard half: turning design into fabrication drawings and finding Indian materials and processes for the gas generator, turbopumps and valves. By his account the first engine was ready towards the end of 1989. Mahendragiri’s test stand wasn’t finished, so that engine was fired at SEP’s facilities in France and worked at the first attempt.
The institution grew alongside it. LPSC’s own timeline says the liquid propulsion units merged into the Liquid Propulsion Systems Unit on 30 November 1985, which became the Liquid Propulsion Systems Centre on 1 June 1987. The name Vikas honors the founder of the programme; the site’s note on Vikram Sarabhai covers why his initials sit on so much of ISRO’s hardware.
Where the Vikas engine flies
Vikas flies on all three of ISRO’s large rockets, but in different jobs. ISRO names each stage with a code, and the codes are what the questions use.
- PSLV, PS2 (second stage). One Vikas engine, 42 tonnes of propellant. It first flew on PSLV-D1 on 20 September 1993, a flight that didn’t place its satellite, IRS-1E, in orbit. The site’s note on the Polar Satellite Launch Vehicle covers the full stack.
- GSLV, GS2 and L40. GSLV borrows PSLV’s second stage as its own second stage, GS2, and adds four L40 strap-ons, each with one Vikas. So a GSLV lifts off with four Vikas engines already burning around its solid core and lights a fifth as its second stage. GSLV-D1 flew this layout first, on 18 April 2001.
- LVM3, L110 core stage. The L110 is the largest liquid stage ISRO has built, with about 115 tonnes of propellant and two Vikas engines. It is air-lit: it ignites about 113 seconds into flight, while the two S200 solid boosters are still firing. It first flew on the experimental GSLV Mk III-X/CARE mission of 18 December 2014, which used a live L110 and a dummy cryogenic stage.
The L110 carried Chandrayaan-3 off the pad in 2023, together with the S200 boosters and the CE-20 upper stage. Credit for any LVM3 mission is shared across all three stages, which is the honest answer to “which engine took India to the Moon.”
Upgrades: high thrust, human rating, throttling and restart
The Vikas of 2026 is not the Vikas of 1993. ISRO has changed it in four dated steps, and each step answers a different need.
High thrust Vikas, 2018. On 15 July 2018, ISRO qualified a high thrust version in a 195-second ground test at the ISRO Propulsion Complex (IPRC), Mahendragiri. ISRO said it would raise the payload capability of PSLV, GSLV and GSLV Mk III, and that the test cleared it for the second developmental GSLV Mk III flight. ISRO’s GSLV page describes the change plainly: a higher chamber pressure, which is why GS2 is rated at 846 kN.
Human rating for Gaganyaan, 2022 to 2023. A rocket that carries people needs larger safety margins than one that carries a satellite. On 20 January 2022, a Gaganyaan Vikas ran for 25 seconds beyond its normal fuel-oxidizer ratio and chamber pressure, deliberately pushed off its design point. PIB reported on 23 March 2022 that the first phase of human-rated Vikas testing was complete. The campaign closed on 6 April 2023 with a 240-second test of the L110-G engine. ISRO’s totals are nine engines, 14 hot tests and 1,215 seconds of firing. The human-rated engine has higher structural margins, an improved assembly process and extra sensors for health monitoring.
Throttling, 2023. On 30 January 2023, ISRO throttled a Vikas down to 67% of its thrust for 43 seconds, stepping the chamber pressure from 58.5 bar through 50, 45 and 40 bar. Throttling is what lets a booster slow itself for a landing.
Restart, 2024 to 2025. In December 2024 and again on 17 January 2025, ISRO shut a Vikas down and lit it again. The January test fired for 60 seconds, paused for 120 and restarted for 7. ISRO links both tests to recovering and reusing stages.
Put the last two together and the direction is clear. An engine that can throttle and restart can, in principle, bring a booster back. ISRO has demonstrated the engine capability; it hasn’t flown a recovered stage.
How Vikas compares with ISRO’s cryogenic and semi-cryogenic engines
Vikas trades efficiency for convenience. The measure of efficiency is specific impulse, the push a rocket gets from each kilogram of propellant, like mileage for a car. ISRO’s GSLV-D1 table gives about 2,890 Ns/kg for the Vikas second stage against 4,510 Ns/kg for the cryogenic stage. Liquid hydrogen and liquid oxygen give far more push per kilogram, but they must be stored at very low temperatures and handled with care.
| Engine | Propellants | Cycle | Thrust (ISRO figure) | Where it flies |
|---|---|---|---|---|
| Vikas | N2O4 and UDMH/UH25, storable | Gas generator | About 800 kN | PSLV PS2, GSLV GS2 and L40, LVM3 L110 |
| CE-7.5 | Liquid oxygen and liquid hydrogen | Staged combustion | 75 kN | GSLV cryogenic upper stage |
| CE-20 | Liquid oxygen and liquid hydrogen | Gas generator | 200 kN nominal | LVM3 C25 upper stage |
| SE2000 (in development) | Liquid oxygen and kerosene | Oxidizer-rich staged combustion | 2,000 kN | Planned SC120 stage of LVM3 |
The pattern that settles most questions is simple: Vikas works low and in the middle, cryogenic engines work at the top. A dense, storable propellant suits the heavy lifting of a lower stage. A light, efficient one suits the final push into orbit. The site’s explainer on rocket propulsion, cryogenic and green propellants walks through the chemistry, and the CE-20 flight acceptance test shows how an individual cryogenic engine is cleared for a mission.
The semi-cryogenic engine is where the Vikas story turns. ISRO states that the SC120 stage, powered by the SE2000, will replace the L110 core stage of LVM3. With an uprated cryogenic stage, that lifts LVM3’s payload to geosynchronous transfer orbit from 4 tonnes to 5 tonnes. The SE2000 runs at 180 bar with a specific impulse of 335 seconds. In LVM3, the successor to Vikas is being built now.
The Vikas engine today
Vikas is in active service and in active development at once. It powers the second stage of every PSLV and the liquid stages of every GSLV and LVM3, and its human-rated version sits inside the Gaganyaan rocket.
The dated record from 2024 to 2026 runs as follows:
- December 2024 and 17 January 2025. Restart tests at Mahendragiri, aimed at stage recovery.
- 28 March 2025. First hot test of the SE2000 power head, the first step towards the stage that will replace L110.
- 29 July 2026. PIB reported that all stages of the human-rated LVM3 (HLVM3), including the L110, were ready for the first uncrewed Gaganyaan mission, G1.
- 5 August 2026. In a Parliament answer released by PIB, the government said ground testing of all HLVM3 propulsion stages was complete and the first crewed mission was targeted for 2027.
- 5 September 2026. ISRO fired the semi-cryogenic power head at 100% thrust for the first time, as the site’s note on the full-thrust test explains. That is not yet a complete engine.
So for the next few years the two engines overlap. Vikas carries Gaganyaan while SE2000 finishes testing. The site’s Gaganyaan mission note tracks the crewed programme, and the comparison of GSLV, NGLV and Falcon Heavy shows where India’s next rockets are headed.
How to study the Vikas engine for exams
The Vikas engine sits in General Studies Paper III under science and technology, in the space and indigenization topics, and in Prelims as a fact-matching item. Prelims tests it through engine-to-vehicle and propellant-to-engine pairings. Science and Technology accounts for 192 of the 1,403 questions in the site’s Prelims question bank.
Mains tests the story around it. Mains 2016 GS Paper III asked “Discuss India’s achievements in the field of Space Science and Technology. How the application of this technology has helped India in its socio-economic development?” Mains 2017 GS Paper III asked “India has achieved remarkable successes in unmanned space missions including the Chandrayaan and Mars Orbitter Mission, but has not ventured into manned space missions. What are the main obstacles to launching a manned space mission, both in terms of technology and logistics? Examine critically.” A human-rated Vikas is a concrete answer to the technology half of that question.
Revise these facts until they come without effort:
- Developer: LPSC, from Viking know-how acquired under the 1974 ISRO-SEP agreement.
- Terms: no cash; ISRO paid in 100 man-years of engineering and pressure transducers.
- Propellants: N2O4 with UDMH or UH25, hypergolic and storable.
- Thrust: about 800 kN, or 80 tonnes.
- Stages: PSLV PS2; GSLV GS2 and four L40 strap-ons; LVM3 L110 with two engines.
- First flight: PSLV-D1, 20 September 1993.
- Human rating: final L110-G test of 240 seconds on 6 April 2023.
Three confusions cost marks. The first is Vikas and Viking: Viking is the French engine, Vikas the Indian one built from its know-how. The second is Vikas and the CE-7.5 or CE-20: Vikas burns storable propellants, the CE engines burn liquid hydrogen and liquid oxygen, and only the CE engines are cryogenic. The third is Vikas and Vikram, which is the Chandrayaan lander and also the name of a private rocket. Vikas is the only one of the three that is an ISRO engine.
| Item | What it is | Propellant | Where it flies |
|---|---|---|---|
| Vikas | ISRO liquid engine | N2O4 and UDMH/UH25 | PSLV, GSLV, LVM3 |
| Viking | French engine for Ariane | Storable hypergolic | Ariane |
| CE-20 | ISRO cryogenic engine | LOX and LH2 | LVM3 upper stage |
| SE2000 | ISRO semi-cryogenic engine, in development | LOX and kerosene | Planned for LVM3 |
The Vikas engine is small as a topic and large as an example. It explains how India turned a barter agreement into self-reliance, and it shows up in a Gaganyaan answer, an indigenization answer and a technology-transfer answer. Learn the seven facts above and the three confusions, and you can use Vikas in a GS Paper III answer without further reading.
Frequently Asked Questions
What is the full form of Vikas engine?
Vikas is read as an acronym of VIKram A. Sarabhai, the founder of India’s space programme, and the word itself means development in Sanskrit. Memoirs of LPSC’s founder director record that T. N. Seshan, then in the Department of Space, coined the name to replace Viking. Both readings are correct and both appear in ISRO histories.
Which fuel does the Vikas engine use?
The Vikas engine burns nitrogen tetroxide as the oxidizer with unsymmetrical dimethylhydrazine (UDMH) as the fuel. LPSC lists the fuel as UH25, which is UDMH mixed with 25% hydrazine hydrate. The pair is hypergolic, meaning the two ignite on contact, and both stay liquid at room temperature.
Is the Vikas engine cryogenic?
No, the Vikas engine is not cryogenic. It uses earth-storable propellants that stay liquid at ordinary temperatures. ISRO’s cryogenic engines, the CE-7.5 and CE-20, burn liquid hydrogen and liquid oxygen, which must be kept extremely cold.
Which rockets use the Vikas engine?
All three of ISRO’s large rockets use it. PSLV uses one Vikas in its second stage (PS2), GSLV uses one in its second stage (GS2) and one in each of its four L40 strap-ons, and LVM3 uses two in its L110 core stage.
What is the thrust of the Vikas engine?
LPSC describes the nominal engine as producing about 800 kN, or 80 tonnes of thrust. ISRO gives 799 kN for PSLV’s PS2 and 846 kN for the high thrust version on GSLV’s GS2. The two engines of LVM3’s L110 stage produce 1,692 kN together.
Where did the Vikas engine technology come from?
It came from France. Under a 1974 agreement with the Société Européenne de Propulsion (SEP), ISRO received the know-how for the Viking engine of the Ariane rocket. India paid no money; it supplied pressure transducers and 100 man-years of engineering work instead.
What is the human rated Vikas engine?
It is the L110-G version of Vikas built for the Gaganyaan rocket, with higher structural margins and extra health monitoring sensors. ISRO completed its qualification with a 240-second test on 6 April 2023, after 14 hot tests on nine engines. Two of these engines power the core stage of the human-rated LVM3.
Will the Vikas engine be replaced?
In LVM3, yes. ISRO plans to replace the L110 core stage, and with it the twin Vikas engines, with the SC120 stage powered by the 2,000 kN semi-cryogenic SE2000 engine. PSLV and GSLV continue to use Vikas, and the semi-cryogenic engine is still in testing.
Practice Questions
Prelims
1. Consider the following statements about the Vikas engine: 1. It uses liquid hydrogen and liquid oxygen as propellants. 2. It powers the second stage of the Polar Satellite Launch Vehicle. Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (b) Vikas burns storable nitrogen tetroxide and UDMH, not cryogenic propellants, and it powers PSLV’s PS2 stage.
2. Consider the following statements: 1. The Vikas engine was developed from know-how for the Viking engine under an agreement with a French firm. 2. Under that agreement, ISRO paid for the technology in cash. 3. The L110 stage of LVM3 uses two Vikas engines. Which of the statements given above is/are correct?
- (a) 1 and 2 only
- (b) 1 and 3 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (b) The 1974 SEP agreement involved no transfer of funds; ISRO paid in pressure transducers and engineering man-years.
3. A pair of rocket propellants that ignite spontaneously on contact, with no igniter, is called:
- (a) Cryogenic
- (b) Monopropellant
- (c) Hypergolic
- (d) Solid composite
Answer: (c) Hypergolic propellants such as nitrogen tetroxide and UDMH ignite on contact, which is why Vikas lights reliably in flight.
4. Which of the following ISRO engines is designed to replace the twin-Vikas L110 core stage of LVM3?
- (a) CE-7.5
- (b) CE-20
- (c) SE2000
- (d) PS4 engine
Answer: (c) ISRO states that the SC120 stage powered by the SE2000 semi-cryogenic engine will replace the L110 stage.
5. Consider the following pairs of launch vehicle stage and engine: 1. GSLV L40 strap-on: Vikas engine. 2. LVM3 C25 stage: CE-20 engine. 3. PSLV PS2 stage: CE-7.5 engine. How many of the pairs given above are correctly matched?
- (a) Only one
- (b) Only two
- (c) All three
- (d) None
Answer: (b) Pairs 1 and 2 are correct; PS2 uses the Vikas engine, while the CE-7.5 powers GSLV’s cryogenic upper stage.
Mains
- The Vikas engine came to India through a barter agreement rather than a purchase. Examine how this model of technology acquisition shaped India’s liquid propulsion capability, and what it teaches about technology transfer today. (15 marks, 250 words)
- Distinguish between earth-storable, cryogenic and semi-cryogenic propulsion, with reference to ISRO’s Vikas, CE-20 and SE2000 engines. Why do launch vehicles use different propellants in different stages? (15 marks, 250 words)
- What does human rating of a launch vehicle involve? Discuss with reference to the qualification of the Vikas engine for the Gaganyaan programme. (10 marks, 150 words)
- Throttling and restart capabilities are being added to ISRO’s older liquid engines. Explain their relevance to reusable launch vehicles and to the cost of access to space. (10 marks, 150 words)
- Critically examine the continued use of toxic hypergolic propellants in India’s launch vehicles in the light of the shift towards cleaner propellants such as liquid oxygen and kerosene. (10 marks, 150 words)