Why ISRO Needs to Develop a Full-Flow Staged Combustion Cycle Engine

Suvankar Majumder

India's space agency, ISRO - Indian Space Research Organization , has achieved remarkable milestones in space exploration. However, as the demands for more efficient and cost-effective space missions grow, it is imperative for ISRO to advance its propulsion technology. One critical area where ISRO can make significant improvements is by developing a Full-Flow Staged Combustion (FFSC) cycle engine. Here's why this technology is essential and why the current gas generator cycle engines are becoming outdated.

Gas generator cycle engines, while reliable and relatively simple to design and operate, have several limitations that hinder their efficiency and effectiveness in modern space missions. Firstly, gas generator engines typically have a lower specific impulse compared to more advanced engine cycles like FFSC. Specific impulse (Isp) is a measure of how efficiently a rocket engine uses its propellant, typically measured in seconds, indicating the thrust produced per unit of propellant consumed per second. A lower Isp means more propellant is needed to achieve the same thrust, leading to higher launch costs and reduced payload capacity. Additionally, gas generator cycle engines are known for their inefficient fuel use. In these engines, a portion of the propellant is burned in a separate gas generator to drive the engine's turbopumps, which supply fuel and oxidizer to the main combustion chamber. The exhaust from the gas generator is often vented overboard and does not contribute to the main thrust, resulting in a loss of potential energy and fuel inefficiency. Furthermore, the gas generator cycle can subject engine components to high thermal and mechanical stress due to the extreme temperatures and pressures involved, reducing the engine's lifespan, increasing maintenance requirements, and raising the risk of component failure during critical missions.

The Full-Flow Staged Combustion (FFSC) cycle is a more advanced and efficient rocket engine technology that addresses many of the limitations of gas generator cycle engines. FFSC engines achieve a higher specific impulse by fully burning all the propellant in the combustion chamber, utilizing all available energy for thrust. This means that less fuel is needed for the same amount of thrust, reducing launch costs and increasing the payload capacity. In an FFSC engine, both the fuel and oxidizer are fully burned in separate preburners before entering the main combustion chamber, ensuring that all available energy is utilized for thrust and significantly improving fuel efficiency compared to gas generator cycle engines. Moreover, FFSC engines distribute thermal and mechanical loads more evenly across engine components, reducing stress on individual parts, enhancing the engine's reliability and lifespan, and lowering maintenance costs.

For ISRO to remain competitive and advance its capabilities in space exploration, developing a cost-effective rocket is crucial. The FFSC engine is a key technology to achieve this goal. With higher specific impulse and improved fuel efficiency, FFSC engines can significantly reduce the cost per launch, making space access more affordable for various stakeholders. Human space missions, which are inherently expensive due to the need for significant resources for safety and life support systems, can become more feasible and sustainable with the adoption of FFSC technology. Lower costs can lead to increased frequency of missions and broader participation in space exploration. Establishing an Indian space station will require numerous launches and significant resources, and cost-effective launch vehicles powered by FFSC engines will make this ambitious project more financially viable, ensuring that the overall expenditure remains within manageable limits. Future missions to the Moon and other celestial bodies will demand the capability to carry heavy payloads and return safely to Earth. The high specific impulse of FFSC engines means less initial mass is needed, as less fuel is required, allowing for more scientific instruments and supplies to be carried.