Rockets are engineering marvels capable of escaping Earth’s gravity and putting humans and satellites into space. They may seem like recent inventions, but the principles of rocket technology date back centuries.
An orbital rocket is a projectile that is propelled forward when chemical compounds are combusted inside its engine to produce hot gases, which are blown at high velocities through its nozzle, producing the thrust needed to propel the vehicle forward, allowing it to reach Space and orbit the Earth.
It has been less than a century since Sputnik 1, the world’s first artificial satellite, was put into orbit by the then-Soviet Union. It ushered in the Space Age, which saw the start of the Space Race between the United States Of America and the Soviet Union.
The United States of America’s success in putting a man on the moon, combined with the end of the Space Race in 1975 and the fall of the Soviet Union in 1991, seemed to dampen the interest and willingness to go to space, as well as the corresponding rocket development.
The Space Shuttle Programme showed much promise, but failure to deliver on a true cost-effective reusable space vehicle, exasperated by the Challenger disaster in 1986 and Columbia in 2003, resulted in the program being canceled in 2011.
This, in effect, ended America’s capability to take astronauts to space for almost a decade. However, private space companies like SpaceX ignited a renewed interest in space exploration and returned American astronauts to space from US soil on May 30, 2020.
Meanwhile, private companies like Blue Origin and Virgin Galactic are developing spacecraft that can take civilians to the edge of space, while Orbital Sciences, Firefly Aerospace, ULA, and other commercial enterprises are also developing their own space programs.
Combined with nations like China and Russia also developing spacecraft that can reach the lunar surface and beyond, it has given birth to a new era in space exploration and rocket development.
The upcoming section will explain what makes rockets work in more detail and describe the various components that make up these launch vehicles. But first, a quick look into the origins and history of rockets.
Where Do Rockets Come From?
Although they seem to be a product of modern engineering, rockets actually date back to the 13th century, when “solid propellant rockets” were used in China for fireworks displays.
During medieval times, countries started using rockets as instruments of war, where they were used to launch projectiles at enemy targets. Iron-cased rockets, though, only started making an appearance during the 18th century in India with the Mysorean rockets.
Modern liquid-propellant rockets as we know them today were invented in 1926 by Professor Robert Goddart, who is considered by many as the father of modern rocket propulsion.
How A Rocket Works
All rockets function/operates on Newton’s Third Law Of Motion, which formally states, “For every action, there is an equal and opposite reaction.”
Essentially, this means that when two forces interact with each other, the one force’s reaction is equal but in the opposite direction of the force applied upon it. The way a rocket works is the perfect example of this law in practice.
A rocket typically works by combining its fuel with an oxidizer in the rocket’s combustion chamber, where it is burned to produce hot gases, which are pushed out the vehicle’s nozzle at supersonic speeds. This, in turn, propels the rocket forward.
In terms of Newton’s Law, the first force that comes into play is the thrust created by the rocket’s engine as it pushes the hot gases out the rear through the nozzle. The thrust from the gases creates the second force, which pushes the vehicle forward as a reaction.
It is this principle that also gives a rocket engine the unique ability to operate in the vacuum of space, unlike aircraft engines used within Earth’s atmosphere. A conventional aircraft requires two conditions to function and stay airborne, which a rocket doesn’t:
- An atmosphere
Oxygen is needed by aircraft engines for burning fuel to function and rotate their turbines/propellers to push air to the back, allowing an aircraft to move forward. Rockets don’t need external oxygen, as they carry their oxygen internally in pressurized tanks.
An atmosphere is necessary for aircraft to stay airborne since the air allows enough lift to be created beneath its wings, which, combined with a high enough horizontal speed, keeps the vehicle in the air.
However, there is no air present in space for a craft to push against to move forward. Since rockets use Newton’s Third Law Of Motion, they don’t need air to maneuver since the gases that are pushed out the back of the rocket thrusters propel the vehicle forward.
How A Rocket Engine Works
The vast majority of rockets designed to travel into orbit and beyond use a liquid propellant rocket engine as opposed to solid rocket boosters (SRBs). Unlike an SRB, a liquid propellant rocket engine can be switched off, restarted, and its thrust controlled.
(Once ignited, a solid rocket booster cannot be switched off, and it continues to burn and produce maximum thrust until its fuel is completely depleted. These rocket boosters typically burn for approximately 2 minutes.)
As a result, the remainder of this section will focus on the operation and characteristics of liquid propellant rocket engines. Wherever the term “rocket engine” is used, it will refer to this specific type of rocket engine.
The hot gases that are ejected through a rocket engine’s nozzle are what makes a rocket work and enable it to create the thrust and velocity to lift itself and heavy payloads off the ground and escape Earth’s gravity.
The rocket engine creates these gases through a series of complex processes:
The illustration above shows the main components of a rocket engine, which create the necessary thrust to escape Earth’s atmosphere. They achieve this through the following sequence of events:
- In short, a fuel and oxidant mixture is burned in the rocket engine’s combustion chamber, which produces hot gases that are accelerated and blown through its nozzle at supersonic speeds. To start this process, the fuel first needs to be transported to the engine:
- Both the oxidizer and fuel are pumped from the internal tanks into the combustion chamber via an oxidizer and fuel pump, respectively, at high speeds.
- To achieve these high speeds, a turbine is spun up through hot gases produced in a gas generator, which drives the pumps to achieve the necessary flow rate. The turbine/pump assembly is known as a turbopump.
- Both the oxidizer and fuel are sprayed and mixed into the combustion chamber at high velocities and under pressure through optimized mixing procedures, where they are combusted to create hot gases.
- The gases are further accelerated through a special nozzle called a converging-diverging nozzle. They enter the narrow part (neck) of the nozzle at subsonic speeds. As they enter the diverging bell-shaped part of the nozzle, they are accelerated to supersonic speeds.
- The hot gases finally exit the rocket engine’s nozzle at supersonic speeds, allowing the launch vehicle to lift its own weight and payload off the launchpad.
This is a very cryptic explanation of how a rocket engine functions. Needless to say, there are much more complex mechanisms and processes involved in making the engine work. These steps, however, described the main components and processes allowing a rocket to function.
Although most rockets use liquid propellant rocket engines to launch them into orbit or deep space, they often use the assistance of solid rocket boosters to lift heavy payloads off the launchpad and assist with the first part of a rocket’s ascent.
A solid rocket booster’s greater power-to-mass ratio, combined with its more simplistic design (and solid fuel-oxidizer mix already added during assembly), makes them ideal and relatively safe to be strapped to the main rocket structure for added power and capacity.
They typically burn and provide maximum thrust for approximately 2 minutes after launch, after which they are separated and ejected from the main rocket to reduce weight and increase aerodynamic efficiency for the remaining rocket stages.
(The solid rocket boosters used for the Space Shuttle Program were the most powerful SRBs ever build and produced 85% of the power during the launch to lift the heavy shuttle and fuel tank off the launchpad.)
What Is A Solid Rocket Booster?
A solid rocket booster (SRB) or solid-propellant rocket works on the same principle a liquid-propellant rocket does in the sense of blowing hot gases at high velocities out its nozzle to propel the rocket forward.
The primary difference between the two engines is that an SRB uses a solid fuel/oxidizer mix for combustion, unlike a liquid-propellant rocket that carries its fuel & oxidizer in separate internal tanks, which are mixed and ignited in a combustion chamber.
The fuel/oxidizer mix is applied to the inside of the rocket’s shell and runs the full length of the rocket. The fuel typically consists of aluminum powder, while the oxidizer is a type of ammonium perchlorate.
A cylindrical hole also running the full length of the rocket acts a the combustion chamber, from where the hot gases are expelled through the rocket’s nozzle.
The more simplistic design allows a solid rocket booster to be much lighter than its liquid propellant equivalent, which gives it a much greater power-to-mass ratio.
It is also easier to transport since the fuel/oxidizer mixture is already added to the rocket during assembly. The absence of complicated mechanisms and loading of pressurized fuel on the launchpad also make these rockets significantly safer.
As already stated, however, an SRB has some significant disadvantages. Once the ignition charge starts the rocket, it cannot be switched off and burn until the fuel is completely depleted (usually after approximately 2 minutes.)
A solid rocket booster also cannot be throttled (its thrust controlled) or restarted at a later stage.
Today, it is still common practice for companies like the United Launch Alliance (ULA), the European Space Agency (ESA), and India’s ISRO to add solid rocket boosters to their “stacks” for added power and increased carrying capacity.
Getting a sense of the complexity of these rocket engines inevitably leads to questions regarding the safety of traveling on these launch vehicles. One can learn more about how safe rockets are and the dangers they pose in this article.
The Parts Of A Rocket
Apart from the propulsion system described earlier in this section, there are other key components that make up a rocket. The 4 main parts of a rocket are:
- Structural System
- Propulsion System
- Guidance System
Each of these parts has a specific and unique function in a rocket’s make-up. By taking a closer look at each component, one can gain a better understanding of its importance and purpose in a rocket’s architecture.
1) Structural System
A rocket’s structural system, or frame and shell, holds all the other components together and shields them from the atmosphere or space. It is basically the rocket equivalent of a plane’s fuselage or the hull of a boat.
The materials used in the construction of a rocket need to be both strong enough to hold the vehicle together and withstand all the dynamic forces put on it during launch and ascent, but also light enough to assist it in escaping Earth’s gravity and achieving orbit.
As a result, strong, lightweight materials like titanium, aluminum, and carbon composites are typically used to build the most critical parts of a rocket’s structure.
Spacecraft used to return to Earth need even more protection since the heat generated during re-entry through the atmosphere is high enough to melt metal. Tiles made from silica (ceramic) fibers are used as heat shields to protect the vehicle during this critical process.
2) Propulsion System
The propulsion system is what drives a rocket through the atmosphere into orbit during launch and also allows it to maneuver in the vacuum of space. The vast majority of a rocket’s mass and its internal structure are made up of the propulsion system.
It primarily consists of the rocket engine (either a liquid-propellant engine or solid rocket booster, or a combination of both), fuel and oxidizer tanks, pumps, and the rocket nozzle.
A modern rocket uses a process called rocket-staging to discard sections of the propulsion system that used up its fuel and is no longer needed to reduce the weight of the vehicle and improve aerodynamics during a launch.
3) Guidance System
A rocket’s guidance system is responsible for guiding its movement and determining the direction it travels in. It is responsible for keeping a rocket upright during launch, controls its trajectory through the atmosphere, and determining its movement in space.
It consists of a series of sensors, onboard computers, radars, and other navigational equipment that allows it to detect the rocket’s orientation and direction and make the necessary adjustments to keep the vehicle on its predetermined heading.
Although it doesn’t always receive the same amount of attention or emphasis as the propulsion or structural system, the guidance system is just as critical for a rocket’s operation, without which it will be unable to function properly.
A rocket’s payload refers to whatever cargo/object/individual(s) a spacecraft needs to deliver or transport into space. Although not crucial for a rocket’s operation, it is the primary reason any rocket is sent into orbit and beyond.
The type of payload any rocket carries depends entirely on the mission of any space launch. If the purpose is to put a satellite into orbit, the satellite (enclosed in purposely-built fairing) will serve as the payload.
Crewed missions will require a spacecraft for carrying humans (like the command module used during the Apollo missions and the Crew Dragon used by SpaceX to send astronauts to the International Space Station). The spacecraft and crew are the payloads in this case.
Rockets are also used to send probes into space to explore the solar system, like the Voyager spacecraft, and more recently, the Cassini probe that studied Saturn in great detail. Scientific equipment like the Hubble Space Telescope can also serve as payloads for rockets.
As this article clearly illustrated, the principles on which a rocket operates seem pretty straightforward and not that hard to understand.
A rocket itself, though, is a very complex piece of engineering, consisting of literally millions of moving parts that have to work together in an exact manner for a rocket to function. A malfunction in any of these components can result in a rocket failure.
This article highlighted the key components of a rocket and how they work together to make a rocket launch possible and allow it to travel into orbit and deeper into space.