Rocket Science — Basics — Part 7 — Solid Propulsion Motors 🚀🧑🚀
While nuclear thermal engines or electric engines or big guns or laser powered engines work well and last long because of its fuel efficiency and best suited for long space travel, we still need chemical rockets (solid & liquid) to launch the rocket into space.
In this blog post, we will look deep into solid propulsion motors.
In solid propulsion motors, the fuel and the oxidizer are mixed together as inert solid and kept in a chamber. This mixture is called propellant. An example for solid propellant is firework rockets.
Once the propellant is ignited, it starts burning with an explosion. Once ignited, we will not be able to control the fire until propellant is exhausted.
This type of rocket motors will produce only lower thrust. As you can see from the above diagram, from the top view, the propellant is filled in a cylindrical chamber and there is hole which can be of any shape in order a have a little bit of control over how much the solid fuel is burnt. Solid propellant with a hole is called as grain.
In the cross-sectional view, we can see that the cylinder where the grain is present is kept inside a motor casing. The combustion occurs inside the hole i.e., only part of the grain (surface area) that is exposed will burn. That means when you start the ignition, then a very small portion of the grain starts to burn. Then, as the grain burns away, more surface area is exposed, so more grain can burn. Nozzle is where the thermal energy is converted into kinetic energy (Any object is in motion is because of kinetic energy). There are different kinds of burn.
The first one is called as progressive burn — In the progressive burn, the hole in the grain increases over time thereby increasing the thrust over time.
The second one is called as regressive burn — In regressive burn, the hole in the grain decreases over time thereby decreasing n thrust over time.
The third one is called as neutral burn — The thrust produced remains constant over the burn period. Neutral burning is particularly advantageous in applications where precise control over thrust is necessary, such as in certain military and aerospace systems. It can also be in star shaped design which also falls under neutral since for most part it is neutral. It is usually used in space shuttle boosters.
Solid rockets can be used as boosters to the original rocket engine, in order to provide an extra thrust. Solid rockets are very huge in size and it is difficult to manufacture it as a single one rather. Instead it is used as multiple smaller ones.
From the above figure, we can see that, there are two solid boosters attached the main engine along with the shuttle. The solid rockets are fired during the launch and it provides additional thrust for take off. Usually, the solid rockets tends to burn completely before it can stop generating exhaust. Usually, the solid boosters will burn out of propellants by two to three minutes after launch and they will be separated from the main engine. The separated engines will be recovered and re-used for further missions. So, boosters helps us to carry more payload into space.
Solid rockets are usually used in ballistic missiles also called as Inter Continental Ballistic Missile (ICBM) because, the propellant can be stored for a very long time and needs less maintenance. It is also used in model rockets and in fireworks.
In the next blog, we will discuss about Liquid Rocket Engines.
Thanks for reading!!!
