There are five main ways that rocket engines are powered. They can be powered physically, chemically, electrically or by using either thermal or nuclear energy. Among these, chemically powered rocket engine is one of the more popular types.
Chemical rocket engines require a propellant that will react in the combustion chamber. Then, the hot gases that the chemical reaction produces will move at a rapid rate, creating something that is called the thrust.
Propellants are comprised of two things – a fuel and an oxidizer. The oxidizer will react with the burning fuel to induce the chemical reaction.
Moving on, let’s check out the many types of chemically powered rocket engines.
In solid rockets, the propellant is a solid called the grain. It is ignitable and self-sustaining. Also, there’s a hollow section inside that increases grain exposure. Gunpowder propellants, zinc-sulfur propellants, composite propellants, and electric solid propellants are a few examples.
The main advantage to solid rockets is that there are no moving parts. It also has decent mass fraction and the grain can be designed to follow a specific thrust schedule.
- Sounding rockets like the VSB-30, Terrier Orion and Black Brant utilize solid rockets.
- Since solid rockets are easy to handle and store, they are often used for air-to-air missiles and ballistic missiles.
- Orbital rockets like the OmegA, Long March 11, and Pegasus use solid rockets.
Unlike solid rockets, hybrid rockets have a separate oxidizer and fuel. The oxidizer, which is kept in a tank, can either be liquid or gas while the fuel is solid.
Hybrid rockets are considered safer since the solid fuel will remain inert without the oxidizer. They are also easier to shut down and the thrust can be throttled.
- Some sounding rockets use hybrid propellants instead of solid rockets.
- A lot of the model rocketry that hobbyists use have hybrid rocket motor systems. This includes the well-known HyperTek systems and the U/C systems.
Just as its name implies, this type of chemically powered rocket engine only requires a single element for its propellant. It also needs a catalyst that will start the decomposition of the propellant.
Common monopropellants include hydrazine, nitrous oxide and hydrogen peroxide. As for the catalyst, you’ll often see granular alumina being used.
Monopropellant rockets aren’t as efficient as some of its counterparts, but this doesn’t stop engineers from using them. This is because they are simple in concept and throttleable.
- Currently, a small spacecraft utilizing a new monopropellant propulsion system is being developed by NASA.
- The EURENCO Bofors company developed the LMP-103S and was used on the Prisma satellite.
If there are single element propellants, there are also ones that use two liquids for its propellants. Once they are injected to the combustion chamber, they are burned to start the chemical reaction. Commonly used fluids include liquid hydrogen and liquid oxygen.
As for the benefits of using this type of propulsion, bipropellant rockets allow for very efficient combustion and lightweight tanks. They’re also throttleable and with proper care, are safe to use.
- Flight vehicles like the Saturn, Energia and some space shuttles use bipropellant rockets.
Turborockets use a combination of turbojets and rockets. An oxidizer like oxygen is then added to the airstream to boost the maximum altitude. Aside from getting better specific impulse, this setup is also cheaper and easier to control.
- The Lockheed A-12, YF-12 and the SR-71 were powered by the Pratt & Whitney J58. This jet engine uses turborocket propulsion.
There are other less used chemically powered rocket engines. For example, precooled jet engines are only at the prototyping stage while the dual mode propulsion rockets have lower performance than bipropellants.