ISRO Successfully Test-Fires A 30 kN Hybrid Motor

On Tuesday, September 20, 2022, the Vikram Sarabhai Space Centre, a key space research center of the Indian Space Research Organisation, successfully tested a hybrid motor at the ISRO Propulsion Complex (IPRC), Mahendragiri, Tamil Nadu. The test-fire was supported by ISRO's Liquid Propulsion Systems Centre (LPSC), a research and development facility. In contrast to solid-solid or liquid-liquid combinations, hybrid motors use solid fuel and liquid oxidizer. ISRO tested a 30 kilonewton hybrid motor using Hydroxyl-terminated polybutadiene (HTPB) as the solid fuel and liquid oxygen as the oxidizer, both of which are chemicals that rapidly react with most organic materials without requiring any energy input.

ISRO said in a mission update that its test of the 30 kilonewton hybrid motor confirmed ignition and sustained combustion for the intended period of 15 seconds. The hybrid motor's performance was satisfactory.

Significance of the Hybrid Motor

The use of liquids in the hybrid motor simplifies throttling, which is the adjustment of propellant flow rates using control valves. Throttling in a liquid-propellant rocket engine thus refers to thrust modulation.

The ability to restart the motor is enabled via control over the flow rate of liquid oxygen. HTPB and liquid oxygen are both green. Liquid oxygen, on the other hand, is easier to handle.

The hybrid motor has the advantages of being a safe propulsion technology, ensuring green propulsion, and being throttable and restartable.

The hybrid motor is "scalable and stackable," according to ISRO, and might open the way for a new propulsion technology for future launch vehicles.