The Indian Space Research Organisation (ISRO) has marked a significant milestone in its propulsion technology by successfully conducting a sea-level hot test of the CE20 cryogenic engine at a thrust level of 22 tonnes.

This test, performed on 10 March 2026 at the ISRO Propulsion Complex in Mahendragiri, utilised a full-area nozzle along with a nozzle protection system and a multi-element igniter. It represents an upgrade from previous sea-level tests, which were limited to 19 tonnes of thrust.

The CE20 engine serves as the powerhouse for the upper cryogenic stage of the LVM-3 (Launch Vehicle Mark-3) launch vehicle, India's workhorse for heavy-lift missions. To boost the payload capacity of future LVM-3 flights, ISRO plans to introduce an uprated C32 stage.

This stage will incorporate the CE20 engine operating at 22 tonnes thrust, necessitating rigorous flight acceptance tests at this elevated level. The recent 165-second test fully qualified the engine for such operations under sea-level conditions.

Sea-level testing of cryogenic engines like the CE20 presents formidable challenges, chiefly due to the engine's high area ratio nozzle. At sea level, the nozzle experiences an exit pressure of approximately 50 millibars, far lower than the ambient atmospheric pressure. This mismatch induces flow separation within the nozzle, generating severe vibrations and intense thermal stresses at the separation plane, which could inflict mechanical damage.

ISRO mitigated these risks through its innovative Nozzle Protection System (NPS), which safeguards the nozzle during ground tests. The system's efficacy was amply demonstrated in this trial, with the engine and test facility performing flawlessly throughout the 165-second duration. All parameters remained within expected bounds, validating the design for operational reliability.

Remarkably, the CE20 engine subjected to this test had already endured a record-breaking 20 hot tests, the highest number for any such engine in ISRO's history. This extensive testing campaign with a single unit has enabled the validation of multiple critical technologies. Among them is ignition via a multi-element igniter, which ensures robust starts across varying propellant tank pressures.

The engine's trials have also confirmed ignition margins tailored for the Gaganyaan human spaceflight programme, spanning a broad spectrum of pre-ignition chamber pressures. Furthermore, it qualified the CE20 for Gaganyaan missions at the original 20-ton thrust level, paving the way for crewed orbital flights.

A standout achievement is the demonstration and qualification of 22-tonne thrust operations, directly supporting the LVM-3 upgradation. The tests showcased bootstrap mode starting of the CE20 without a dedicated start-up system, a vital feature for potential in-flight restarts that enhance mission flexibility.

Indigenous innovations shone through in the qualification of turbopump bearings and sensors, all developed domestically. These components reduce reliance on foreign suppliers and bolster India's self-reliance in cryogenic propulsion. The NPS itself, qualified for high area ratio nozzles during sea-level hot tests, addresses a longstanding hurdle in ground-testing advanced engines.

This success underscores ISRO's prowess in cryogenic technology, building on decades of iterative development since the CE20's inception. The engine, fuelled by liquid hydrogen and liquid oxygen, delivers high specific impulse essential for orbital insertion. With the LVM-3 already proving its mettle in missions like Chandrayaan-3 and Aditya-L1, the uprated C32 stage could lift payloads beyond 8 tonnes to geostationary transfer orbit.

Looking ahead, this test clears a key hurdle for upcoming LVM-3 missions, including commercial satellite launches and Gaganyaan. It aligns with India's broader ambitions in reusable launch vehicles and next-generation systems like the Next Generation Launch Vehicle (NGLV). By mastering sea-level testing of high-thrust cryogenics, ISRO edges closer to cost-effective, high-capacity access to space.

ISRO