Successful cryogenic engine start enables enhanced mission flexibility for ISRO

by Simon Mansfield
Sydney, Australia (SPX) Nov 21, 2025
ISRO has qualified the CE20 cryogenic engine for thrust levels between 19 and 22 tonnes for single-start flight operations, supporting demanding launch requirements for the LVM3 upper stage. The engine is certified for human-rated flights, such as the Gaganyaan missions, ensuring operational reliability under rigorous conditions. Traditionally, engine ignition is performed using propellant tank head pressure, followed by stored gas initiation of the turbopumps.

Upcoming missions will introduce a need for multiple in-flight restarts of the CE20 engine, supporting complex, multi-orbit satellite deployments. With the present restart system, each additional ignition relies on separate start-up gas bottles and hardware, imposing mass penalties that reduce available payload space. Developing boot-strap mode startup-allowing the engine to initiate on its own, without external gas bottles or auxiliary systems-is critical for enhancing future mission flexibility.

ISRO successfully performed a key test of the CE20 engine in boot-strap mode on November 7, 2025, at the High-Altitude Test facility at Mahendragiri. The experiment simulated space-like vacuum conditions and operated for 10 seconds. Engineers utilized multi-element igniters in both the thrust chamber and the gas generator to initiate the sequence. After ignition of the thrust chamber, the gas generator followed under tank head conditions, and both turbopumps started directly-eliminating the need for stored gas assist. The engine exhibited stable boot-strap mode build-up and steady-state functioning.

This marks the first verified boot-strap mode start for a gas-generator cycle cryogenic engine without external assistance, making a major advance in propulsion for launch vehicle upper stages. The new capability is expected to improve LVM3 restart reliability and expand ISRO's mission design options for future launches.

Related Links
Indian Space Research Organisation (ISRO)
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