Rocket propulsion is a fascinating technology. A technology that generates thrust which moves any aircraft through the air. But do you know the rocket technology was invented by the Chinese in the 13th century? Well, of course rockets were then not used for any kind of spacecraft, but for military use instead. One such ancient rocket launch was the “wasp nest,” an arrow launcher which was launched by the Ming dynasty army in 1380.
Rockets were not used in industrial or scientific works till the 20th century, when it enabled space exploration by humans for the first time. Thus far we know that missiles are also a type of rocket, but are there any other types of rockets? Let’s find out.
Basically, rockets can be classified into two broad categories-
Based on Propulsion
1. Solid-propellant rocket
The Columbia Space Shuttle was launched with the help of two solid-fuel boosters Image Courtesy: NASA
Solid-propellant rockets are simply those rockets whose engines generate thrust using solid propellants. What are solid propellants you ask? They are basically composites, composed of a mixture of solid oxidizer such as ammonium nitrate in a binder agent with powdered energetic compounds and additives like aluminium.
Because of their reliability and low maintenance costs, solid fuel rockets are used in various military operations since the 14th century. However, due to their low performance, these are not used to power modern large launch vehicles, but they are still employed as primary boosters to increase vehicle payload capacity.
2. Liquid Fueled Rocket
Liquid Fueled Rocket Schematic Image Courtesy: Nicholas W. Beeson
As the name indicates, liquid fueled rockets use liquid propellants to generate thrust. In contrast to solid propellant, liquid ones are composed either of single or two chemicals (bipropellants). Liquid propellants are largely preferred over solid propellants due to their high density and efficiency levels.
The first recorded flight of such rocket was in 1926, when professor Robert H. Goddard experimented on a vehicle using liquid oxygen and gasoline as propellant. Do you know that Sputnik, the first human made satellite into space was propelled by a liquid-fueled rocket, which was followed by the American Apollo 11 mission.
Liquid propellants are also used in hybrid rockets, where a rocket motor uses one solid and one gas or liquid propellants over two phases.
3. Plasma Propulsion Rocket
A plasma propulsion engine in 1961 Image Courtesy: NASA
In a plasma propulsion engine, the thrust is generated from quasi- neutral plasma (where ion and electrons are packed in equal numbers). Over the years, many institutions have worked or currently working on plasma-fueled engines including Iranian Space Agency, Australian National University and the European Space Agency.
VASIMR (Variable Specific Impulse Magnetoplasma Rocket) is the newest types of plasma fueled rocket propulsion engines that ionize the propellant into a plasma with the help of radio waves. One of the many advantages of a plasma propulsion engine is its higher specific impulse value or Isp than almost any other type of rockets.
While plasma engines are still not entirely utilized commercially, a few small-scale versions have already been successfully deployed and tested. In 2011, NASA, along with a Massachusetts-based propulsion company launched the first ever Hall thruster (plasma) into space on board Tacsat-2 experimental satellite.
4. Ion Rocket
Ion engine test firing at NASA’s Jet Propulsion Laboratory
Ion engines use electrostatic or electromagnetic force to accelerate ions in order to produce thrust. In other words, instead of forcing out the pressurized gas of a nozzle, the ion thrusters use xenon gas and accelerate them to extremely high velocities. They are more efficient than conventional rockets, especially when outer space travel is in question.
That’s because ion engines cannot operate in the lower atmosphere, where ions are present outside the engine. The first ever successful deep space mission to use ion thrusters was NASA’s Deep Space 1 in 1990. Later, JAXA launched the Hayabusa spacecraft in 2003, which is still in operation.
Based on Use
5. Rocket Car
You may have heard about jet cars, but what about rocket cars? In contrast to a jet powered car, a rocket car carries both fuel and oxidizer, which eliminates the need for a compressor and an air inlet, which in turn reduce the total weight and minimize drag. These cars can gain extremely high speeds in fairly quick time period due to their astronomical thrust-to-weight ratio.
Rocket cars were once popular among drag racing communities in the United States, but after hydrogen peroxide became too expensive, it lost its edge and was eventually banned in the country for safety reasons. However, they are still operating in some parts of Europe.
6. Rocket Pack
A Rocket pack is a low-power propulsion device that carry individuals from one place to another over small distances. These devices generally use hydrogen peroxide as fuel, but oxygen and methane powered liquid fueled rocket packs were also developed in 1920s. Earliest hydrogen peroxide powered rocket belt was developed by now defunct company Bell Aerosystems for the U.S Army in the early 1950s.
7. Rocket Powered Aircraft
Messerschmitt Me 163
Rockets can also be used in aircraft. Rocket planes can attain much higher speeds than a similar sized jet aircraft, but only over smaller distances. They were first engineered by the Germans during the First World War. Due to the fact that these engines don’t need atmospheric oxygen, rocket powered aircraft are perfect for high-altitude flights.
Rockets are also used to assist the main propulsion units, which is widely known as rocket assisted take off or RATO. One of the popular rocket powered aircraft was the North American X-15 Hypersonic rocket that holds the official world record for the highest speed ever achieved by any manned aircraft i.e. 4,520 miles per hour.
Due to the heavy use of propellants, rocket engines are mostly used in interceptor aircraft and spaceplane.