ISRO successfully conducts crucial test for semi-cryogenic engines required for ‘heavy’ space launches in future

PHTA is a significant precursor test done to validate the integrated performance of some of the engine’s critical subsystems, such as the gas generator, turbo pumps, pre-burner and control components. The test involves performing a hot-firing for an extremely brief duration of not more than 4.5 seconds.

Earlier, in July 2023, a similar test attempt at the space agency’s facility at Mahendragiri had to be aborted following a technical glitch. And since then, the ISRO team has continued working on developing this semi-cryogenic engine that offers an enhanced thrust of 2,000 kiloNewton (kN).

A propulsion system, be it the earth-to-orbit or the in-space, is the one that gives a rocket muscle power to lift off from the Earth, across the dense atmosphere and later reach its destination. The selection of an appropriate propellant system is based on the thrust required, reusability, cost and core competency. ISRO has been using environment-friendly and green propellants like Liquid Oxygen (LOX), Liquid Hydrogen (LH2) and LOX-kerosene-based propulsion systems.

Sixteen hot tests were completed to characterise pre-burner ignition. (Source : ISRO)

The cryogenic engine uses liquid oxygen and liquid hydrogen. Handling liquid hydrogen is challenging, given that it needs to be stored at minus 253 degrees Celius and it is highly inflammable. Whereas a semi-cryogenic engine uses a liquid oxygen – kerosene combination, where kerosene is readily storable; this combination offers advantages like high-density impulse (with respect to cryogenic), less toxic (with respect to storage) and cost-effectiveness.

During his address, the ISRO chief elaborated on the overall ongoing research activities that were directed towards improving the performance of Launch Vehicle Mk III (LVM3). He said that the LVM3 will be equipped with the C32 cryogenic upper stage for many of its future space missions. The advantage of C32 over its predecessor, C25, is that the latter allows carrying additional quantities of propellant onboard, thereby adding more life to the space mission.

“With C32 in the upper stage, the payload (carriage) will increase by 25 per cent. We are working on two systems to increase the spacecraft’s launch capacity from 4 tonnes to 5.1 tonnes at Geosynchronous Transfer Orbit, that too, without increasing the cost. In addition, we are also developing a Liquid Oxygen (LOX) and kerosene-based propulsion system which will be powered by a 2,000-tonne thrust engine,” he said.

‘Development of NGLV on track’

With activities for the unmanned and manned Gaganyaan missions picking pace, Narayanan said that the development of the Next Generation Launch Vehicle (NGLV), which will be deployed for all the Gaganyaan missions, was on track. NGLV is a new generation, human-rated launch vehicle offering both high payload capability and reusability. With a reusable first stage, it offers a maximum payload capability of 30 tons to Low Earth Orbit.

“It is a new vehicle. The first and second stages will use LOX engines and the upper stage will be a cryogenic stage. The design is complete and we have moved on to the development,” said Narayanan, who is also the Secretary, Department of Space.

ISRO is developing technologies that will allow propulsion systems to recover and reuse the launch vehicles. Recently, the space agency tasted success in the experiments performed towards recovering the first stage NGLV, Narayanan said.

The ISRO chairman further shared that a team has been identified to study the feasibility of developing future advanced propulsion systems. These systems are expected to work as follows: after a normal take off, just like in an aircraft, it would switch to a cryogenic engine when required, travel and cover long geographical distances, typically of the order of thousands of kilometres across continents, in just a few hours.