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Methane as Rocket Fuel The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical, which is called a monopropellant, or a mix of two chemicals, which is called bipropellants. Bipropellants can be further divided into two sub-categories: hypergolic propellant, which ignites when the fuel and oxidizer make contact, and non-hypergolic propellant which requires a source of ignition. For a chemical rocket, the highest specific impulse means the most propellant-efficient engine, producing either the most thrust for a given amount of propellant, or providing the desired thrust with less propellant. A higher specific impulse equals to a higher effective exhaust velocity, allowing the rocket to achieve a greater change in momentum from the same propellant mass. This efficiency is primarily determined by the propellant chemistry. For the best result, the usual combination is liquid hydrogen and liquid oxygen. Until now....

  Aeolipile, Hero's engine As it can sound interesting, the Chinese Han Dynasty that prevailed around 200 BC is well known for developing rockets which were used for fireworks at that time. However, very early invention of the basic principle for a jet engine goes already back to the Hero of Alexandria (around AD 67). Hero of Alexandria was an Egyptian mathematician and inventor who had invented several machines utilizing water, air, and steam. An illustration of Hero's aeolipile, source: Wiki In Figure, you can see schematic illustration of Hero's aeolipile. The Aeolipile, also known as Hero's engine, is a simple, bladeless reaction steam turbine invented by Hero of Alexandria in the 1st century AD. This is considered as first device, based on reactive thrust principle way before Newton's laws, especially the third law of motion.  The name aeolipile is derived from the Greek name Aeolus, the Greek god of the wind, and word pila, meaning ball. The name basically mea...

Raptor is a family of rocket engines which are developed and manufactured by SpaceX for use in Starship. This rocket engine marks significant step in rocket engineering. It is designed with full-flow staged combustion fuel cycle and use of methane as a fuel, known as Methalox. SpaceX announced the development of the Raptor engine in 2012, with the first full-scale engine testing in September 2016. These advanced, reusable methane-oxygen engines are the primary power source for the SpaceX Starship system.  The engine is powered by cryogenic liquid methane and liquid oxygen, known as Methalox. Refined liquid methane as well as LNG are typically used as a fuel for rockets in combination with oxygen. For example it is used in the TQ-12, BE-4, Raptor, YF-215, and Aeon engines. A Raptor 1 rocket engine, SpaceX's factory in Hawthorne, California; source: Wiki The Raptor engine is a full-flow staged combustion cycle engine, which allows for higher efficiency and performance compared t...

Why are sizes of rocket nozzles in second or upper-stage engine bigger than those used by sea-level engines? A sea-level optimized Raptor nozzle (on the left) stands next to a vacuum-optimized Raptor nozzle (on the right) at the SpaceX development facility in McGregor, Texas. Credit: SpaceX  Well, the answer is quite simple. A vacuum- optimized  rocket engine nozzle is bigger then a sea-level engine nozzle since it needs to match the significantly lower air density in the upper atmosphere and in space. Let's have a look in more detail. For a rocket engine is important to operate at its most efficient level, which means to produce the maximum amount of thrust. It is a key for the hot gases exiting the engine nozzle to match the external air ambient pressure. The importance of this is clear when you realize that the air pressure at sea level is about 1000 millibars, or 100 kPa, and it decreases with increasing altitude. The value quickly decreases with altitude to 100 millibars,...

Specific impulse  I was many times using the term specific impulse. So, let's speak about it in more detail.    Specific impulse (usually abbreviated I sp ) is a measure of how efficiently a reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust. A propulsion system which has a higher specific impulse uses the mass of the propellant more efficiently than a propulsion system with lower specific impulse. Now, in the case of a rocket, this means less propellant is needed for a given delta-v, so that the vehicle attached to the engine can more efficiently gain altitude and velocity. For all vehicles specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation: Thrust is force, the thrust obtained from the engine (newtons or pounds force), g 0 is the standard gravity, which is nominally the gravity at Earth's surface (m/s2), I sp is the specific impulse measured (secon...

Exercise: 1. Single stage rocket:  Before a rocket begins to burn fuel, the rocket has a mass of  m r,i =2.81×10 7 kg, of which the mass of the fuel is  m f,i =2.46×10 7 kg. The fuel is burned at a constant rate with total burn time is 510 s and ejected at a speed v e = 3000 m/s relative to the rocket. If the rocket starts from rest in empty space, what is the final speed of the rocket after all the fuel has been burned? What we know: initial rocket mass m r,i =2.81×10 7 kg initial mass of the fuel m f,i =2.46×10 7 kg t = 510 s v e  = 3000 m/s So, we can calculate the dry mass of the rocket m r,d =m r,i -m f,i =0.35×10 7 kg. The mass ratio is then R = m r,i  /m r,d =8.03. So, the final speed of the rocket is then: V r,f =Δv r =v e lnR=6250m/s. 2. Two-stage rocket:  Now, we have similar example, the same rocket as in the previous example, but the fuel will be burnt in two stages ejecting the fuel in each of the stages at the same relative speed (v e  =...