What’s in News:

• Skyroot Aerospace successfully tested Dhawan-1 and  became the country’s first privately developed fully cryogenic rocket engine running on two high-performance rocket propellants — liquid natural gas (LNG) and liquid oxygen (LoX). 
• The indigenous engine was developed using 3D printing with a superalloy.
  • Superalloys, or high performance alloys, are alloys that exhibit excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. The development of superalloys has primarily been driven by the aerospace and power industries.

What the company plans to do

• The company plans to put its first launch vehicle, Vikram-1 based on a solid propulsion engine, in space. This was after successfully designing and developing the solid propulsion rocket engine, the first private firm in the country to do so.
• They also plan to launch the first private space launch vehicle using cryogenic engine Vikram-2 into orbit in two years.

Related information

Cryogenics

• A cryogenic rocket engine is one that employs cryogenic fuel or oxidizer, which means that its fuel or oxidizer (or both) are gases that have been liquefied and kept at extremely 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. Specific impulse (a measure of the efficiency) achievable with cryogenic propellants (liquid Hydrogen and liquid Oxygen) is much higher compared to earth storable liquid and solid propellants, giving it a substantial payload advantage. 

Rocket Propellants

• The propellant is a chemical mixture composed of a fuel and an oxidizer that is burned to produce thrust in rockets.
  • Fuel is a substance that burns when combined with an oxidizer to power a vehicle.
  • The oxidizer is a substance that releases oxygen for use in combination with a fuel. The mixture ratio refers to the oxidizer-to-fuel ratio.
• Propellants are classed based on their state, which might be liquid, solid, or hybrid.

1. Propellants in liquid form: The fuel and oxidizer are stored in separate tanks in a liquid propellant rocket and are fed to a combustion chamber where they are combined and burned to produce thrust.

• Advantages: Although liquid propellant engines are more sophisticated than solid propellant engines, they have some advantages. The engine can be throttled, halted, or restarted by managing the flow of propellant to the combustion chamber.
• Disadvantages: The primary issues with liquid propellants are oxidizers. Storable oxidizers, like nitric acid and nitrogen tetroxide, are exceedingly poisonous and highly reactive, although cryogenic propellants can also have reactivity/toxicity difficulties when stored at low temperatures. 

• There are three types of liquid propellants utilised in rocketry: petroleum, cryogens, and hypergolic.
• Petroleum fuels are processed from crude oil and are a complex mixture of hydrocarbons
• Cryogenic propellants are liquefied gases held at extremely low temperatures, with liquid hydrogen (LH2) serving as the fuel and liquid oxygen (LO2 or LOX) serving as the oxidizer.
• Hypergolic propellants and oxidizers that spontaneously ignite when they come into touch with each other and do not require an ignition source. Hypergolics are useful for spacecraft manoeuvring systems due to their ease of start and restart. 
• 2. Solid propellant rockets are the most basic of all rocket designs. They are made of a casing, usually made of steel, that is filled with a mixture of solid compounds (fuel and oxidizer) that burn quickly, ejecting hot gases through a nozzle to produce thrust. 

• Advantages: Unlike liquid propellant rockets, solid propellant rockets are much easier to store and handle. The high propellant density also results in a small size.
• Disadvantages: Unlike liquid-propellant engines, solid propellant engines cannot be turned off. When ignited, they will burn until the propellant is depleted. 

3. Hybrid propellant engines: These engines are a cross between solid and liquid propellant engines. One of the components is solid, usually the fuel, while the other is liquid, usually the oxidizer. The liquid is injected into the solid, which also functions as a fuel reservoir and a combustion chamber.

• The fundamental benefit of such engines is that they have great performance, comparable to solid propellant engines, but the combustion may be slowed, stopped, or even restarted. Because it is difficult to apply this concept to very big thrusts, hybrid propellant engines are rarely produced.

 References:

1. https://www.thehindu.com/news/cities/Hyderabad/citys-rocketmen-duo-aim-for-the-skies/article37859035.ece
2. https://www.isro.gov.in/gslv-d5-gsat-14/indigenous-cryogenic-engine-and-stage
3. https://history.nasa.gov/conghand/propelnt.htm
4. http://www.braeunig.us/space/propel.htm