ISRO VSSC Director explains significance of latest hybrid rocket motor test

The IndianSpace Research Organisation (ISRO) recently completed a successful test of what it called a hybrid motor. Conventional motors that are developed by ISRO burn a chemical combination that is in similar states (either solid or liquid), i.e., they arepowered by solid fuel and solid oxidizers or liquid fuel and liquid oxidisers. However, the latest Hybrid motor uses a Solid fuel Hydroxyl-terminated polybutadiene (HTPB) as fuel and liquid oxygen (LOX) as an oxidizer.

According to ISRO, the test of flight equivalent 30 kN hybrid motor demonstrated ignition and sustained combustion for the intended duration of 15 seconds. The motor performance was satisfactory, the Indian space agency added.

Speaking to WION, Dr S. Unnikrishnan Nair, Director, Vikram Sarabhai Space Centre highlighted the advantages of the hybrid motor and its future applications. Vikram Sarabhai Space Centre (VSSC) is the lead Centre of the Indian Space Research Organisation (ISRO) under the Department of Space (DOS), Government of India. The Centre is named in fond memory of Dr Vikram A Sarabhai, the great visionary and the father of the Indian Space Programme. VSSC pioneers in rocket research and launch vehicle projects of ISRO.

He said that rocket motors powered by solid fuels and solid oxidizers are a single-use category. This essentially means that they are discarded (fall back into the ocean) after they burn out the fuel contained within. These motors also cannot be re-started and fired again. However, in the case of motors that use liquid fuel and a liquid oxidizer, the motors can be restarted and the amount of thrust can be throttled (controlled).

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In the hybrid motor, the use of Liquid oxygen as oxidizer enables throttling of the motor and the control over the flow rate of the Liquid oxygen enables the re-start capability.

Simply put, the hybrid motor tested by ISRO combines the high-thrust capability of solid-fuelled motors and the re-start and throttle capability of liquid-fuelled motors. "Hybrid motors can be used for applications such as spent stage recovery (partially-reusable rockets). This technology is scalable and can be used for future rockets where there is a need for restart, throttle ability, more safety and greener fuel" Dr Nair elaborated.

He also added that the 30kN hybrid motor was designed using the Rohini Sounding Rocket (RSR300) motor case and hence the new hybrid motor could be flight tested in the sounding rocket. Sounding rockets are smaller rockets that are meant to conduct upper atmospheric and space research. They are smaller and simpler in terms of technology and carry very less (up to 100kg payload) to altitudes between 80 km and 475 km when compared to orbital rockets that carry tons of payload to various orbits.

Queried about the specific purpose of firing the new hybrid motor for a short duration of 15 seconds, Dr Nair replied thatduration was chosen because the most important part is the starting transient and how quickly the thrust gets stabilised from the ignition. He added that the duration of motor firing could be easily stretched for longer periods.

(With inputs from agencies)

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