Hello readers!! Welcome to another article on rocket technology. In the last article, I discussed the Liquid Propulsion System. In this article, I will focus on a special type of liquid propulsion engine, Cryogenic Engine.

You may have heard of this term before. If not, don’t worry, we will keep our discussion very simple and knowledgeable as well. But, if you are new to this topic, please go through the previous article for a better understanding.

What does the term Cryogenic mean?

The term “Cryogenics” is associated with the branch of physics that deals with the effects and behavior of materials in very low temperatures.

Here a question may be raised, is there any bordering temperature for Cryogenics??..... No, there is no specific bordering temperature for cryogenics.

Scientists assume a gas to be cryogenic if it can be liquified at or below -150°C.I

As an example, Hydrogen is a cryogenic fluid and it can be liquified at -253°C.

What is a cryogenic rocket engine?

A Cryogenic Rocket Engine is an engine that uses cryogenic fluid as fuel and oxidizer. Both the fuel and oxidizer are liquified gases and they are stored and handled at very low temperatures in the cryogenic rocket engine.

So, maintaining the temperature that is far less than 0°C and execute the operations at that temperature is a challenge for rocket engineering. This challenge leads to a much-complicated structure of a cryogenic rocket engine than the structure of a usual liquid propulsion engine or a solid propulsion motor.

Importance of Cryogenic Rocket Engine:

In the choice of fuel and oxidizer, Oxygen is the simplest oxidizer and Hydrogen is the simplest fuel. So, we can consider hydrogen-oxygen combination is one of the most preferable propellants for rocket engines as they release a high amount of energy when combusted and generate high thrust to propel a rocket.

But the problem with the hydrogen-oxygen combination is both of them are gas at normal temperature. It is possible to store them as pressurized gas, but this would require large and heavy storage tanks, which would make spaceflight almost impossible.

So, these gasses are cooled to sufficiently low temperature and liquified and then stored in tanks. They are handled at that temperature and used as the propellant in the Cryogenic engine.

Various fuel-oxidizer combination has been used as propellent of the cryogenic engine. But generally, the hydrogen-oxygen combination is used as they are easily and cheaply available.

History of Cryogenic Engine:

he world's first cryogenic engine, RL10, was developed in 1962 in the United States of America by Marshall Space Flight Centre (NASA) and its first successful flight took place on 27th November 1963. It was mainly developed for Lunex Lunar Lander. On the first flight, it was used in the upper stage of Atlas Launch Vehicle.

This RL-10 engine was one of the most important weapons of NASA’s space exploration.

On 26th February 1966, another cryogenic engine, J-2, developed by NASA, completed its first flight successfully. This engine is considered as one of the main factors of the success of SATURN-V Launch Vehicle in many different missions including the Appolo-11 mission ...

IMPORTANT NOTE:-

(A) In GSLV Mk-I, Russian cryogenic engine, KVD-1 was used in the third stage of the launch vehicle. In GSLV Mk-II, KVD-1 was replaced by India’s CE-7.5 engine. In GSLV MK-III, it is further replaced by India’s CE-20 engine.

(B) In India, Liquid Propulsion Systems Centre (ISRO) developed the first Indian Cryogenic Engine, CE-7.5 under Cryogenic Upper Stage Project (CUSP).

(C) Unfortunately, the first flight of the CE-7.5 engine ended with a failure in 2010. Later in 2014, this engine completed its first flight successfully.

(D) In 2017, Liquid Propulsion Systems Centre (ISRO) developed another cryogenic engine, CE-20. It completed the first successful flight on 5th June 2017.

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