Explained | India: ISRO tests cryogenic engine for Chandrayaan-3. Significance and tech

The Indian space agency has successfully conducted a hot test of its CE-20 Cryogenic Engine for the soon-to-be third mission to Moon, Chandrayaan-3. The Indian Space Research Organisation (ISRO) is in the midst of carrying out some of the most crucial tests for the upcoming lunar mission.

What happened during the recent test?

The hot test for the CE-20 Cryogenic Engine which will power the Cryogenic Upper Stage (CUS) of the LVM3 launch vehicle during the Chandrayaan-3 mission was successfully conducted at the space agency’s Propulsion Complex, Mahendragiri in the Indian state of Tamil Nadu, said ISRO.

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The “hot test” on February 24 was done for a planned duration of 25 seconds at the High Altitude Test Facility. A hot test is an assessment of an engine’s performance under conditions which are similar to when it is running in a real vehicle and checks all the parameters to ensure that the engine is working properly.

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“All the propulsion parameters during the test were found satisfactory and closely matched with predictions,” said ISRO. The cryogenic engine will be further integrated with the propellant tanks, stage structures and associated fluid lines to realise the fully integrated flight cryogenic stage.

What is a cryogenic engine/cryogenic stage?

Cryogenics refers to the study of the change in chemical properties and behaviour of materials at very low temperatures of at least -150 degree Celsius. The engines created using this technology are among some of the most powerful ones. The cryogenic stage is a very complex system, but is more efficient and provides more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellant rocket stages.

Cryogenic engines carry liquid propellants at extremely low temperatures and typically make use of liquid oxygen (LOX) and liquid hydrogen (LH2). While the former liquefies at -183 degrees Celsius, the latter liquifies at -253 degree Celsius. ISRO’s cryogenic stage is powered by a CE-20 engine which works with the LOX-LH2 propellants combination.

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It is designed by the Liquid Propulsion Systems Center, in collaboration with Vikram Sarabhai Space Centre, ISRO Propulsion Complex and Satish Dhawan Space Centre. The tanks can carry over 27,000 kg of fuel and fire for at least 720 seconds.

Cryogenic engines are highly efficient rocket propulsion systems and suitable for the upper stages of a rocket since they have a higher specific impulse (a measure of the efficiency or thrust) which enhances its payload capacity.

Major components of a cryogenic rocket engine include an igniter, combustion chamber (thrust chamber), fuel cryo pumps, fuel injector, oxidiser cryo pumps, gas turbine, cryo valves, regulators, fuel tanks and a rocket engine nozzle.

How does it work?

The cryogenic stage is the last stage of the launch of a space vehicle where the fuel LOX and LH2 stored using cryogenics is released from their respective tanks and are fed by individual booster pumps to the main turbopump to ensure a high flow rate of propellants into the combustion chamber.

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While the LH2 acts as the fuel, the LOX acts as the oxidiser which explosively reacts with the hydrogen.

In simple terms, since there is no air in space, it is impossible to burn anything. Therefore, rockets carry their own oxidiser, which when mixed with fuel, burns and produces thrust (the force which moves a rocket through the air).

Cryogenic engines: India’s ordeal and success story

Today, India is one of the only six countries including the US, France (European Space Agency), Russia, China, and Japan which have developed their own cryogenic engines.

However, the Indian journey to become a part of this exclusive group was marked by global politics and decades of hard work spearheaded by ISRO.

In the early 1990s, the erstwhile Soviet Union Space Agency had agreed to transfer the cryogenic technology held by the five aforementioned countries except for India.

But the US, Japan, Europe and China were against it. It was seen as an aspect of Cold War politics prevalent at the time.

Eventually, the move was blocked by the US by invoking the Missile Technology Control Regime (MTCR) (an association to stop the proliferation of missiles that could be used for mass destruction) and imposed sanctions on both India and the Soviet Union space agencies.

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This came after the Soviet Union had reportedly said that it considered India an exception and both countries assured that the technology would not be used for the military but only for communication and weather satellites.

Years later, the then US President Bill Clinton and his Russian (since the Soviet Union had disintegrated) counterpart Boris Yeltsin came to a decision about Moscow selling seven cryogenic engines to India but not transferring the technology.

When ISRO was founded in 1969, it undertook the task of developing cryogenic engines.

Decades later, the Indian space agency successfully conducted its first cryogenic engine test in 2003.

However, the first successful flight was not until 2014 when the Indian space agency launched the GSLV-DF rocket powered by its indigenous-produced cryogenic engine from Sriharikota, an island off the Bay of Bengal coast and dubbed as the spaceport of the country.

About Chandrayaan-3

The Chandrayaan-3 mission will follow Chandrayaan-2 and demonstrate end-to-end capability in safe landing and roving on the lunar surface, the Indian space agency had said previously. It will comprise a lander and rover configuration and will be launched by GSLV MkIII from the Satish Dhawan Space Centre in Sriharikota.

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The propulsion module will carry the lander and rover configuration to 100 km of the Moon’s orbit and will also study the spectral and polarimetric measurements of Earth from there with the help of Spectro-polarimetry of Habitable Planet Earth (SHAPE) payload. However, the final launch date of the mission is yet to be announced but is said to be towards the second or third quarter of this year.

(With inputs from agencies)

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