Sriharikota, Nov 20: The Indian Space Research Organisation (ISRO) on Wednesday announced a major breakthrough in cryogenic propulsion, confirming the successful boot-strap mode start of its CE20 cryogenic engine — a key step toward enhancing restart capability and increasing mission flexibility in future LVM3 flights.Boot-strap mode refers to starting a gas-generator cycle cryogenic engine without any auxiliary start-up system. Currently, the CE20 engine, which powers the upper stage of the LVM3 rocket, is qualified for thrust levels between 19 and 22 tonnes with a single start, and is also cleared for the upcoming Gaganyaan missions.
During normal operations, the engine is ignited under tank-head conditions, and its turbopumps are started using a stored-gas start-up system. However, future multi-orbit missions will require multiple in-flight restarts. Under the existing configuration, every restart needs an additional gas bottle and related systems, reducing payload capacity. Hence, a boot-strap mode start — where the engine reaches steady operation without external assistance — is crucial.
To achieve this, ISRO conducted a boot-strap mode start test on November 7, 2025, at the High-Altitude Test (HAT) facility of the ISRO Propulsion Complex in Mahendragiri, Tamil Nadu. The test was held under vacuum conditions for 10 seconds.
A multi-element igniter was used in both the thrust chamber and gas generator. After the thrust chamber was ignited under tank-head conditions, the gas generator was lit and the turbopumps were successfully spun up without the start-up system, leading to a stable boot-strap mode operation.
ISRO confirmed that the test successfully demonstrated the engine’s build-up and steady-state running in boot-strap mode — a significant advancement for India’s heavy-lift rocket missions.