ISRO's Leap Towards Self-Reliance in Rocket Propulsion Systems

ISRO's Breakthrough in LOX-Methane Engine Technology

ISRO has made significant strides in developing LOX-Methane engine technology for its future rockets. The Indian space agency has initiated the development of LOX-Methane engines for its Next Generation Launch Vehicle and future heavy lift launch vehicle, leveraging clean combustion and low maintenance benefits.

Liquid propulsion activities in ISRO began with the development and delivery of small thrusters for SLV-3 and Secondary Injection Thrust Vector Control (SITVC) systems. The agency later delivered similar control systems for ASLV. A quantum jump in liquid propulsion came through the collaborative development of the 800kN Vikas engine for PSLV, which is today the workhorse liquid engine of ISRO used in PSLV, GSLV & LVM3.

ISRO has also mastered the much-coveted Cryogenic propulsion by developing indigenous cryogenic engines & stages for the GSLV and LVM3 launch vehicles, thereby making the nation self-reliant in launching communication satellites. Similarly, on the satellite front, ISRO started with the development & delivery of monopropellant thrusters, moved on to bi-propellant Liquid Apogee Motors (LAM) needed for the INSAT communication satellites.

ISRO has also developed throttle-able propulsion systems for Chandrayaan-3 lander mission that enabled the nation to be the first to land a spacecraft near the south pole of the Moon. Globally, liquid propulsion systems have witnessed a shift towards LOX-Methane engines, considering the clean combustion, low maintenance (useful for reusability) and the ability to be synthesized on Mars from CO2 and water ice (useful for future Mars missions and human colonization).

In this context, ISRO has identified LOX-Methane engines as the primary propulsion systems for its Next Generation Launch Vehicle (NGLV) and also the future heavy lift launch vehicle required for the Indian crewed lunar landing mission targeted for 2040. Considering the potential of LOX-Methane propulsion systems in future launch vehicles, ISRO initiated development activities in this area in 2019, to understand critical aspects of liquid oxygen–liquid methane (LOX-methane) propellants combination on engine operation.

A 20-ton thrust technology demonstrator engine, the LM20-TD, has been developed and tested, marking a significant step towards self-reliance in rocket propulsion systems for ISRO. The demonstrator engine operated on the gas generator cycle with major subsystems including Thrust Chamber, fuel rich gas generator, Fuel Turbopump, LOX Turbopump, Igniter, Start-up system, Control components, Flow control elements, mixture ratio control valve with electric drive.

The design adequacy of all subsystems was assessed through theoretical analysis prior to the development tests. Test sequence was derived using an in-house developed mathematical model. The existing cryogenic engine test facility at IPRC was augmented for the purpose of testing the LM20 demonstrator engine and one cold flow test and five hot tests were carried out successfully.

With the data obtained from these tests, vital inputs were derived on chill down characteristics, thrust chamber and gas generator ignition, engine starting, combustion and rotor-dynamic systems performance for a LOX- Methane engine. The inputs derived from the Technology Demonstrator engine have been gainfully utilized in the design of LOX-Methane engine that is under development in ISRO.

In 2023, ISRO formally initiated the development of key technologies for a 1100kN LOX-Methane engine (LME1100), that focused on the development & validation of key technologies leading to the different subsystems of the engine viz. turbopumps, igniter, gas generator and thrust chamber. LME1100 engine is designed as a Gas Generator Cycle (GGC) based engine where the design is optimized for industry friendliness and cost effectiveness.

With the active involvement of industrial partners across the nation, more than 70% of the LME1100 engine components have been realized through Additive Manufacturing. The Gas Generator (GG) is realized through additive manufacturing and is under qualification tests at IPRC. The sub-scale version was subjected to extensive testing at lab level to derive the ignition sequence using the spark torch igniter and to characterize the additively manufactured injector elements during ignition.

The first ignition test of the full-scale Gas Generator was successfully carried out on October 9, 2026 and a series of similar tests are planned to evaluate the performance under different conditions. Sub-scale thrust chamber hot test campaign was also carried out. The test series was used to demonstrate the novel realization techniques planned to be eventually adopted in the full scale thrust chamber.

The hot test campaign was also used to characterize the injector elements designed for LME1100 thrust chamber in actual operating conditions for varying design and operating parameters. The hot test campaign carried out at IPRC not only helped in finalizing the optimal injector configuration, but also helped in demonstrating the working of oxidizer rich and fuel rich spark torch igniters.

The LOX and Methane turbo-pump systems are also realized through various industries across the nation and the hardware are under different levels of sub-system testing at LPSC and IPRC. The 3D printed LOX pump impeller was subjected to spin test up to the rated operating speed at LPSC. Dynamic sealing systems and turbo-pump bearings have also been realized through Indian industries and are under qualification tests at IPRC.

ISRO's development of LOX-Methane engine technology is a significant step towards self-reliance in rocket propulsion systems. The agency's efforts in developing LOX-Methane engines for its Next Generation Launch Vehicle and future heavy lift launch vehicle will enable the nation to launch communication satellites and crewed lunar missions with greater efficiency and reliability.