ISRO Fires Its Semi-Cryogenic Engine to 175 Tonnes, Within Reach of a Full 200-Tonne Powerplant
ISRO fired the power head of its semi-cryogenic engine at 175 tonnes of thrust on 24 June 2026 — 88 percent of full rating — clearing the way for a full 200-tonne test of a cleaner, LOX-kerosene engine meant to boost the LVM3 and the Next Generation Launch Vehicle.
Manik Gupta
Founder and editor of DeepTech India. Manik writes about India's frontier technology ecosystem — AI, semiconductors, space, quantum, robotics and biotech — translating research and policy into clear, reliable reporting.
On 24 June 2026, the Indian Space Research Organisation pushed its long-running semi-cryogenic engine programme to a new high, firing the engine's Power Head Test Article (PHTA) at a thrust level of 175 tonnes — roughly 88 percent of the engine's full rated capacity. The hot test, conducted at the ISRO Propulsion Complex (IPRC) in Mahendragiri, Tamil Nadu, was the first time the power head had run at this thrust, and the eighth in a continuing series of qualification firings.
A staircase to full thrust
The PHTA is the beating heart of the engine minus its thrust chamber: it bundles together the gas generator, the high-pressure turbopumps and the associated feed systems that drive propellant into the combustion chamber. Getting that assembly to run stably at high power is the hardest part of building a large liquid-fuelled engine, which is why ISRO has been climbing toward full thrust in deliberate steps. Earlier tests in the campaign cleared 94 tonnes (about 47 percent of rated thrust) and 120 tonnes (about 60 percent) before the latest 175-tonne run.
During the June test, ISRO reported that the main turbopumps delivered outlet pressures of 400 and 500 bar — the kind of pressures needed to force propellant into the chamber against the back-pressure of combustion. Demonstrating steady-state operation at these conditions is the key milestone the agency has been working toward before committing to a test of the complete engine.
Cleaner propellants, heavier payloads
The engine — a roughly 200-tonne (2,000 kN) class powerplant in ISRO's semi-cryogenic line — burns liquid oxygen together with a refined, purified kerosene that the agency calls Isrosene. That LOX-kerosene combination is non-toxic and more environmentally benign than the hypergolic propellants used in some of India's existing rocket stages, and it offers more thrust per unit of stage mass than the current liquid core.
That matters because the semi-cryogenic engine is being developed to power a new high-thrust stage intended to lift the payload capacity of India's LVM3 heavy-lift rocket and to serve as a building block for the planned Next Generation Launch Vehicle. A more powerful, cleaner-burning core stage is one of the levers ISRO is pulling as it tries to bring down the cost of putting heavy satellites — and, eventually, crew — into orbit.
Why this test counts
India already flies cryogenic upper-stage engines, but a large semi-cryogenic booster engine has been a long-standing gap in its propulsion portfolio. Engines in this class are technically demanding precisely because of the turbopump pressures and thermal loads the power head must survive. Walking the PHTA up to 88 percent of rated thrust without failure is strong evidence that the design margins hold, and it de-risks the far more expensive integrated engine tests still to come.
What comes next
ISRO has said the successful 175-tonne run paves the way for the next phase, in which the engine will be evaluated at its full rated thrust of 200 tonnes, and ultimately as a complete engine including the thrust chamber. ISRO Chairman V. Narayanan described the recent propulsion testing as a "major achievement and milestone," while cautioning that the broader human-spaceflight roadmap remains technology-intensive and will involve multiple uncrewed missions before any crewed flight.
For a programme that has spent years inching up the thrust curve, the June test is a meaningful step: the hardest subsystem has now run at close to full power, and the path to a flight-ready Indian semi-cryogenic engine is shorter than it was a week ago.
Sources
- ISRO successfully tests next-gen semi-cryogenic rocket engine — Organiser
- From 175 tonne thrust to future Moon missions — Business Today
- ISRO Achieves 175-Tonne Semi-Cryogenic Engine Hot Test — IndianWeb2
- India's ISRO Achieves Milestone With Semi-Cryogenic Rocket Engine Hot Test — Bloomberg
- ISRO successfully tests semi-cryogenic engine at 175-tonne thrust milestone — Telangana Today
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