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Principle of Rocket Propulsion with Low Pressure
Rocket propulsion theory is the foundation of aerospace theory. A rocket engine is a propulsion device that provides strong thrust to enable spacecraft to reach the required orbital velocity. Its operation is based on the principle of direct reaction motion, which is particularly beneficial for high-speed flight.
So, what is direct reaction motion?
According to the basic laws of Newtonian mechanics, for two objects interacting with each other, the action and reaction forces always exist simultaneously, with equal magnitudes and opposite directions. Therefore, any movement, in a general sense, is a reaction motion. Here are two examples: first, a ship; due to the rotation of the propeller on the water, the reaction force from the water propels the ship forward; second, a jet engine; as the fuel within the engine burns and expands, the expanding gas is ejected backward at high speed, and the engine receives a thrust in the opposite direction of the gas ejection, causing it to move forward.
When studying the phenomenon of thrust from a general perspective, there is no difference between the two types of motion described above; both move under the influence of reaction forces. However, based on the characteristics of the reaction forces, there are differences: in one case, the engine itself cannot cause motion; it is merely an energy source. If there is an engine on a ship but no impeller, then no matter how powerful the engine is, the ship will not move. Therefore, in addition to the engine (energy source), there is an intermediate mechanism between the engine and an external object (such as water in this example), which interacts with the external object and bears the resulting reaction force. This intermediate mechanism is commonly referred to as a propeller (such as the impeller in this example); in the second case, there is no intermediate mechanism, and thrust is generated by the reaction of gas against the engine itself. We call the first type of motion indirect reaction motion, and the second type direct reaction motion. Of course, there are also mixed types where direct and indirect reaction motions coexist, such as turbine Kaplan engines, where part of the engine’s energy is transferred to the propeller, while another part generates direct reaction motion through gas flow.
Jet propulsion is a type of direct reaction motion. So what is jet propulsion? It is a propulsion method in which matter is ejected from the object being propelled in the form of gas.
The substance ejected by the jet propulsion laboratory is called propellant; the engine that generates thrust using jet propulsion is called a jet engine. During operation, the interacting objects are the engine itself and the high-speed airflow ejected from its interior. The reaction force generated by the high-speed airflow acts on the engine itself, in the opposite direction of the airflow—this is known as thrust.
Jet engines are divided into two main categories:
First is the air jet engine, which uses the atmosphere to generate a jet stream. For example: using oxygen in the atmosphere as an oxidizer to burn fuel and produce a gas jet; or heating air in a nuclear heat exchanger, and then discharging it through a nozzle.
Second is the rocket engine, which is a jet engine that carries all the propellant materials itself. For example: it contains oxidizers and combustion agents to generate a gas jet.
The thrust and velocity achieved by the rocket engine far exceed those of conventional propulsion methods. This type of engine does not rely on surrounding medium conditions and can operate in space environments. This characteristic ensures that the thrust generated by the engine remains constant regardless of air acceptance capabilities at various flight speeds. This also enables the rocket (engine) to achieve much higher flight velocities than any other type of engine. Secondly, due to direct reaction motion with no intermediate mechanisms, and the absence of motion mechanisms that limit operating temperature in the main ejection channel, the structure of the rocket engine is simple, yet the thrust produced is very large..

Product Name: Little Rocket

Model Number: FJ901 Little Rocket

Size: 19*5.5*11 CM