Ahead of Gaganyaan, ISRO’s CE-20 engine already has a notable legacy

Ahead of Gaganyaan, ISRO’s CE-20 engine already has a notable legacy

Subject: Science and tech

Section: Space Sector

What is Gaganyaan:  The Gaganyaan Mission is India’s ongoing project to send a 3-day manned mission to the Low Earth Orbit (LEO) of 400 km with a crew of 3 members and bring them safely back to Earth.

Preferred fuels for rocket motors:

• Engineers prefer to use liquid fuels because they are less bulky and flow better than solid fuels.
• Hydrogen as fuel is also desirable because on combustion it generates the highest exhaust velocity.

Comparison:

• For example, combusting hydrogen with oxygen results in an exhaust velocity of 4.5 km/s.
• With unsymmetrical di methyl hydrazine and nitrogen tetroxide — the combination used by the second stage of the PSLV rocket, e.g. — is around 3.4 km/s.
• Thus, hydrogen is a desirable fuel for rocket motors.

Cryogenic engine:

• It uses propellants at extremely low temperatures.
• It uses liquid fuels (Oxygen liquifies at -183 deg C and Hydrogen at -253 deg C) that are cooled to very low temperatures.
• A Cryogenic rocket stage is more efficient and provides more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellant rocket stages.
• It requires special equipment to store and transport liquid hydrogen and special engines to power a rocket.

Three Cryogenic Engines of ISRO: 

• KVD-1, CE-7.5, and CE-20.
• CE-7.5 and CE-20 are India-made. Although the design of the CE-7.5 is based on the KVD-1 supplied by Russia (as the Soviet Union) in the early 1980s.
• The GSLV Mk lII launch vehicle uses CE-7.5 engines to power the third stage of its ascent.

A cryogenic engine operation requires a cryopump, special storage tanks and turbopumps.

Cryopump is a device to trap and cool the hydrogen and oxygen to liquid form.

Turbopump is required to move the cooled fuel and oxidiser to the engine.

The CE-7.5 engine: 

• It uses the staged-combustion cycle.
• In a pre-burner, a small amount of the fuel is combusted.
• The resulting heat drive the turbine to power the turbopump.
• Once the turbopump brings the rest of the fuel and oxidiser to combustion chamber
• Then hydrogen is combusted to power main engine plus two vernier thrusters.
• The exhaust from the pre-burner is also routed to the combustion chamber.

CE-20 Engine:

• It uses the gas-generator cycle
• It discards the exhaust from the pre-burner instead of sending it to the combustion chamber.
• This reduces fuel efficiency
• The CE-20 engine is easier to build and test.
• ISRO has dropped vernier allowing the engine’s nozzle to make small rotations or gimbal to adjust the rocket’s flight path.
• Thus, CE-7.5 engine is lighter and have higher fuel-use efficiency.
• The CE-20 engine achieves a higher maximum thrust (~200 kilonewton v. 73.5 kilonewton) with a shorter burn duration.

Mission using CE-20 Engine:

• LVM-3 rockets using the CE-20 in the third stage (the first stage: two solid-fuel boosters and the second stage: two liquid-fuelled Vikas 2 engines ) have already launched
• Chandrayaan-2 mission
• Chandrayaan-3 missions
• The 5.8-tonne payload of the commercial One Web mission in 2022.
• Upcoming: The first uncrewed Gaganyaan test flight (G1) which is tentatively scheduled for mid-2024.

LVM-3: Launch Vehicle Mark-3

• The LVM-3 has 3 stages:
• The first stage is in the form of 2 S200 boosters straps to the sides of the rocket body; combust a solid fuel called hydroxyl-terminated polybutadiene.
• The second stage is powered by Vikas Engines (combust a liquid fuel) either nitrogen tetroxide or unsymmetrical dimethylhydrazine.
• The final stage is Powered by a cryogenic engine. It combusts liquified hydrogen with liquified oxygen.

LVM-3 capabilities: 

• It can lift up to eight tonnes.
• It is launched in low-earth orbit
• It is the vehicle of choice for the first Gaganyaan mission,
• It improves India’s self-sufficiency vis-à-vis launch capabilities
• Its launch costs are low.

What is human-rating:

Human-rating entails processes to verify particular errors like the failure of a particular component, happen at less than a particular rate.

ISRO’s human-rating tests: 

• to ISRO -The four CE-20 engines had been hot-fire tested for a cumulative 8,810 seconds against the minimum human rating qualification standard requirement of 6,350 seconds.
• In a cold-flow test, fluids flow through the engine but have no combustion or exhaust, whereas combustion or exhaust is present in hot-fire test.