Human rating of ISRO’s cryogenic engine

Context: In a major milestone for India’s space sector, Indian Space Research Organisation (ISRO) has accomplished the human rating of its cryogenic engine (CE-20), which powers the cryogenic stage of the human-rated LVM3 launcher for India’s first human space flight mission Gaganyaan.  

• Human-rating refers to rating a system that is capable of safely transporting humans.

Major Highlights: 

• The ground qualification tests for the human rating of the CE-20 engine involved life demonstration tests, endurance tests and performance assessment under nominal operating conditions as well as off-nominal conditions with respect to thrust, mixture ratio and propellant tank pressure. 
• ISRO has also successfully completed the acceptance tests of the flight engine identified for Gaganyaan mission, tentatively scheduled for the second quarter of 2024. The engine will power the upper stage of the human-rated LVM3 vehicle and has a thrust capability of 19 to 22 tonnes with a specific impulse of 442.5 seconds.

Gaganyaan Mission: 

• The Gaganyaan project envisages demonstration of human spaceflight capability by launching a crew of three members to an orbit of 400 km for a three-day mission, and bring them back safely to the Earth, by landing in the sea. 
• Launcher: Launch Vehicle Mark-3 (LVM3/ GSLV Mk III).

Launch Vehicle Mark-3:  

• Launch Vehicle Mark-3 or LVM3 (previously referred as the Geosynchronous Satellite Launch Vehicle Mark III or GSLV Mk III) is a three-stage medium-lift launch vehicle developed by the Indian Space Research Organisation (ISRO).
• Stages: GSLV Mk III is a three-staged launch vehicle.
  • First stage- Solid fuel S200 stage. Two rocket boosters use 200 tonnes of solid fuel to lift off the rocket.
  • Second stage- Liquid fuel L110 stage. 
  • Third stage- Cryogenic fuel C25 stage uses 25 tonnes of a mixture of liquid hydrogen and liquid oxygen.
    • This upper stage, developed entirely in India, uses the CE-20 cryogenic engine. 
    • This high-thrust engine burns liquid hydrogen and liquid oxygen at very low temperatures for exceptional efficiency and payload capacity.
• Primarily designed to launch communication satellites into geostationary orbit. It is also due to launch crewed missions under the Indian Human Spaceflight Programme (Gaganyaan Mision).
• The LVM3 is one of the most powerful rockets in ISRO's fleet, and it is capable of launching heavier payloads than its predecessors (GSLV-MKII).
  • Payload capacity:
    • 4,000 kilograms to geosynchronous transfer orbit (GTO).
    • 10,000 kilograms to low Earth orbit (LEO).

Indigenous cryogenic engine technology in India: 

• India has managed to develop its own cryogenic engine, a result of decades of research and development. This engine has an entirely Indian design, developed within ISRO, and uses a different process to burn the fuel. 
• This indigenously developed cryogenic engine is deployed in LVM3, ISRO’s most powerful rocket so far, which carried the Chandrayaan-2 and Chandrayaan-3 missions, among others. LVM3 has had seven flights till now, without any trouble. 

Some important reasons why cryogenic engines are used in rockets:

• High specific impulse: Cryogenic engines use liquid hydrogen and liquid oxygen as propellants. These propellants are stored at extremely low temperatures (around -253°C for hydrogen and -183°C for oxygen), which gives them a high energy density, i.e, they pack a lot of energy in a small amount of mass.
  • When these propellants burn, they release a lot of energy compared to their mass, or have high specific impulse. 
  • High specific impulse means more thrust per kilogram of propellant (High thrust to weight ratio). This allows rockets to carry less fuel, reducing their overall weight and allowing them to carry heavier payloads or travel further. Higher thrust is beneficial for:
    • Overcoming Earth's gravity: Launching a rocket out of Earth's gravity well requires immense thrust. Cryogenic engines provide the necessary power to achieve this initial escape velocity.
    • Manoeuvring in space: Once in space, cryogenic engines allow for precise manoeuvring and course corrections due to their high thrust and controllability. 
• Throttling Capability: Cryogenic engines are designed to be throttleable, i.e., they have the ability to vary or adjust their thrust levels during flight. This capability is essential for precise control during ascent, orbit insertion, manoeuvring, controlled reentry and other critical phases of a rocket’s journey.
• Greater fuel efficiency: The combustion process in cryogenic engines is cleaner and more complete, releasing more energy and generating more thrust. Rockets with cryogenic engines need less fuel to achieve the same results, making them more cost-effective.

Challenges: 

• Complexity: They require complex and expensive infrastructure to store and handle extremely cold propellants.
• Cost: The initial development process of cryogenic engines is generally more expensive than other types.