Rockets are the most effective way to escape Earth’s atmosphere and reach space. While astronomers and scientists have dreamt of exploring the universe for centuries, the technical issues of traveling into space were only solved in the 19th century.
Gas Dynamics Laboratory, the Soviet research and development lab, played a crucial role in the initial development of rocket technology. In 1921, they began focusing on solid propellant rockets, which eventually resulted in the first launch in 1928. Although the rocket flew for only 1,300 meters, it was a big milestone.
In 1926, Professor Robert Goddard of Clark University connected a supersonic nozzle to a high-pressure combustion chamber, doubling the thrust and increasing the engine efficiency from 2% to 64%. He used liquid propellants instead of gunpowder to reduce the weight and maximize the effectiveness of rockets. His work started a whole new era of modern rockets.
We have come a long way since then. Today’s rockets are far more complex and used for various purposes, such as launch vehicles for artificial satellites, space exploration, and human spaceflight.
To help you understand the design of these intricate machines, we have listed some of the most common parts of a rocket and their purpose. We have covered all important components, including the ones that power the vehicle and control and correct the direction of motion.
Table of Contents
5. Structural System
A rocket’s structure (or frame) is made of lightweight yet strong materials. Although space shuttle rockets weigh hundreds of thousands of kilograms, they are designed to be as light as possible so they can carry loads to Earth’s orbit using minimum fuel. At the same time, the structure needs to be strong enough to withstand the extreme temperatures of the upper atmosphere.
The structure is made of different components:
The nose cone of Atlas V Rocket carrying the Mars 2020 Perseverance rover | Credit: NASA/KSC
The top of the rocket is conically shaped to modulate oncoming airflow behaviors and reduce aerodynamic drag. Inside this cone is a chamber where satellites, auxiliary equipment, plants, or animals may be carried. The outer surface of the cone is designed to withstand extreme temperatures produced by aerodynamic heating.
The rocket body holds the fuel, oxidizer, and engine. Fuel and oxidizer together make propellant. Fuel is a chemical; it can’t burn or power the rocket engine without an oxidizer (oxygen). Since rockets travel into space (where there is no air), they must carry oxygen with them.
The amount of fuel and oxidizer that needs to be carried is calculated precisely for every mission. The rocket can only leave the ground if it produces a thrust greater than the total mass of the vehicle. The higher mass would mean you need a more powerful engine, which in turn would require more fuel. That’s why every ounce of weight counts, and mass is trimmed to just the bare essentials.
In a typical rocket, about 90% of the total mass is propellants, 6% accounts for the structure (body, engine, fins), and 4% can be the payload (astronauts, satellites, additional instruments, food).
Fins are attached to the lower part of the rocket body. They provide stability during flight. In other words, they maintain the vehicle’s orientation and intended flight path. They work the same way as feathers placed at the tail of an arrow. The drag on the feathers keeps the tail at the back so that the point of the arrow can travel straight into the wind.
Without fins, the rocket would lose control within seconds after leaving the launcher. This is because several forces (including aerodynamics, gravity, as well as force generated by the engine) act upon the vehicle simultaneously. Once the center of gravity goes below the center of pressure, the rocket becomes unstable.
When building a rocket, designers consider various factors such as the shape, number, size, and location of the fins. They are typically located at the rear unless the rocket has an onboard automated guidance system.
The body of the rocket is made of several strong but lightweight materials. Duralumin, for example, is the most common alloy used in rocket compartments. The alloy comprises aluminum, copper, and small amounts of manganese and magnesium, which make it harder and stronger. Since it has low weldability, duralumin parts are usually bolted or riveted.
The space race between the United States and the Soviet Union led to the development of numerous robust aluminum alloys containing up to 10 constituents. Most of them, including aluminum and lithium alloys, are still used to make multi-stage rocket components.
Another common alloy is stainless steel. It is superior to aluminum alloys in many aspects. It is hard and lightweight; it can withstand extreme loads without deformation, and it is quite cheaper than aluminum alloys. Nowadays, it is used to build propellant tanks (with a wall thickness of about 0.5-1 mm)
Copper alloys are also used in some components. Chromium-copper alloy, for example, is used to make the inner wall of the rocket engine. It can withstand extreme heat (3,500 Kelvin) bursting out of nozzles during the launch.
Moreover, titanium is used to build impellors for rocket engines. Unlike other materials, titanium and its alloys do not corrode in an aerospace environment. They have excellent resistance under most oxidizing, neutral, and inhibited reducing conditions. But since they are heavier and more expensive than aluminum and steel alloys, they are used in very limited amounts.
4. Payload System
The payload depends on the space mission. The same rocket can be modified to launch payloads for different objectives, such as satellites for weather monitoring, communication, spying, or exploring outer space.
However, the most valuable payload carried by any rocket is human beings. The United States military rockets like Titan, Atlas, and Redstone carried the Gemini and Mercury spacecraft into orbit in the early 1960s. The Gemini 3 spacecraft carried two astronauts to low earth orbit to study the effects of space flights.
Putting satellites and intricate instruments into space is not as easy as it sounds. The payload not only needs to be lifted to space, but it must also arrive safely in its desired orbit. There should be no physical damage due to extreme acceleration caused by rocket thrust or rapid changes in the magnitude or direction of the acceleration caused by engine throttling. Moreover, biological, chemical, or electrical payloads can also be damaged by sudden changes in temperatures or pressure and radiation exposure from cosmic rays.
To ensure this doesn’t happen, most payloads are built to withstand certain amounts of rough conditions on the way to their destination. Plus, they are enclosed in a nose cone (also called payload fairing), which keeps them safe from extreme temperatures and pressures.
Relative payload sizes of the three-man Apollo spacecraft, the two-man Gemini spacecraft, and the one-man Mercury spacecraft | Credit: NASA
The Saturn V rocket holds the record for launching the heaviest and largest payload to low Earth orbit and beyond. It was used to launch 140,000 kilograms of payload into low Earth orbit, including the unused propellant required to send the Apollo and Lunar Module to the Moon.
Between 1967 and 1973, Saturn V launched a total of 24 astronauts to the Moon and one space station (named Skylab) to the low Earth orbit.
3. Guidance System
The guidance system of a rocket consists of sophisticated radars, sensors, communication equipment, and onboard processing units. It has two primary functions:
- Provide stability during the launch
- Control the vehicle during maneuvers
Scientists have developed many techniques to control rockets during flight. Most of these techniques involve analyzing all the forces acting on the vehicle, which contribute to the final motion. Once the system has all the data, it can precisely calculate the path to fly into the target orbit.
Early rockets (as well as a few current ones) generally use movable fins at the rear. These fins provide the correct amount of aerodynamic force to the vehicle, making it stable during flight.
The newer rockets (developed in the late 1970s and later) utilize a system of thrust vectoring called gimbaled thrust. In this system, the exhaust nozzle is moved from side to side to generate the control torque. As the nozzle moves, the direction of the thrust changes relative to the rocket’s center of gravity.
Overall, the guidance system has three components:
- Input: It includes sensors, radio and satellite links, and other data sources.
- Processing: It contains multiple CPUs that process data and calculate the ‘next step’ to achieve a proper heading.
- Output: The data is then sent directly to the digital autopilot to take necessary actions. The autopilot continuously provides feedback to the guidance system on the state of flight controls.
Raptor engine developed by SpaceX
The aim of the rocket engine is to produce thrust. While different types of engines work in different manners, they all are based on Newton’s third law of motion: every action has an equal and opposite reaction.
The engine throws mass (in the form of high-pressure gas) in one direction to produce a reaction in the opposite direction. The mass comes from the fuel.
Unlike an airplane engine, a rocket engine requires fuel plus an oxidizer (the source of oxygen). This is because space doesn’t have any oxygen, so the rocket has to carry its own. The fuel and oxygen are mixed and ignited in a combustion chamber. This reaction generates exhaust, which is passed through a nozzle to create thrust.
The amount of thrust produced is based on how much mass flows through the engine and what is the exit velocity of the gas. (When the fuel burns, it turns from solid to gas or liquid to gas.)
There are two main types of rocket engines: solid propellant rockets and liquid propellant rockets.
The former can be stored for years without significant propellant degradation, and they can be launched reliably. However, due to their poor performance (compared to liquid-fuel rockets), they are not currently used for major missions. They are used to launch lighter payloads (less than 2 tons) to low Earth orbit.
Liquid-fuel rockets, on the other hand, are heavier and more complex to store and handle. However, they deliver a higher thrust per unit weight of the propellant burned. They can be easily shut down once started, which provides an extra layer of safety. These engines can be designed to start and shut down multiple times during flight for orbital maneuvering.
Some rocket engines are powered by electricity (arcjet rocket and resistojet rocket) or nuclear energy (gas core reactor rocket and fission-fragment rocket). However, they are currently very inefficient and require a lot of research and tests.
The propellant is mass stored in a tank before being used as a high-velocity mass that is ejected (in the form of gas) from the rocket nozzle to generate thrust. The most common propellants include fuels like kerosene or liquid hydrogen and oxidizers like nitric acid or liquid oxygen.
The fuel is burned with an oxidizer in a combustion chamber to generate massive amounts of hot gas. Modern rockets like Falcon Heavy, Falcon 9, Atlas V, Long March 6, Angara, and Zenit use liquid oxygen with highly refined kerosene. The mixture is used for the first-stage boosters that lift off at ground level.
Some propellants (called monopropellants) don’t need to be burned to undergo a chemical reaction. They can be decomposed using a catalyst to produce hot gas. Hydrogen peroxide, nitrous oxide, and hydrazine are perfect examples of such monopropellants.
Early rockets used solid propellants, which contained a mixture of granules of solid oxidizers, such as ammonium perchlorate, ammonium dinitramide, and ammonium nitrate, in a polymer binding agent, with powders of explosive compounds like HMX or RDX. Stabilizers, burn rate modifiers, and plasticizers are also added to solid propellants.
More To Know
What are the different stages of a rocket?
Modern rockets use two or more states, each containing its own engine and propellant. These stages can be either parallel (attached alongside another stage) or series (mounted on top of another stage). Every stage is optimized as per its specific operating environment. For instance, upper stages are designed to function properly in low atmospheric pressure at higher altitudes.
Dividing a rocket into different stages makes it simpler to accelerate the vehicle to its target speed and height. While 2-stage rockets are common, rockets with as many as 5 different stages have been launched successfully.
How many rockets have been sent into orbit or beyond?
Although there is no official record for this, the number of launch attempts has increased significantly in the recent decade. Major contributing factors include the rise of the Chinese space industry as well as private manufacturers like SpaceX.
In 2021, a total of 144 orbital launch attempts were made (133 of those launches were successful). The numbers surpassed the highest number of attempts in 1967 (139 attempts, of which 122 were successful) and the past record for successful orbital launches in 1976 (125 successes out of 131 missions).
How much does it cost to launch a rocket?
Earlier missions (such as NASA’s space shuttles) used to cost an average of $1.6 billion per flight, which equates to about $30,000 per payout of payload (inflation-adjusted price) to reach low Earth orbit. Over the last decade, NASA has managed to bring down the cost to $152 million per launch.
However, SpaceX rockets have been far more efficient in terms of pricing. According to the company, it costs $67 million per launch or about $1,300 per pound of payload to reach low Earth orbit.
Where can I see a rocket launch?
You can witness the live rocket launch from Kennedy Space Center Visitor Complex. It is the closest public viewing area, about 5-7 miles from the launch pads. You can purchase tickets days before launch schedules to experience the full power of mighty rocket engines.