Rocket Engines & Rocketry

FIELDS OF STUDY: Aerospace Engineering; Spacecraft Propulsion; Space Technology

ABSTRACT: Rockets are the vehicles that make space exploration possible. These powerful vehicles are launched from Earth and travel through the sky and into outer space. A rocket’s engine is the component that propels the rocket upward. Newton’s laws of motion play an important role in rocketry, as does mass fraction. Rockets have a rich history and continue to evolve.

Fundamentals of Rockets

A rocket is a vehicle that typically travels to outer space. The term "rocket" can also refer to the engine that propels the vehicle. Besides space travel, rockets are often used in war. Both major types of rocket use a propellant, which is the chemical substance that launches the rocket. A propellant can be either solid or liquid and is usually a mixture of fuel and oxidizer. The oxidizer allows the fuel to burn, which is a key component to propelling the rocket. Oxygen is the most common oxidizer. As their names imply, a solid-propellant rocket uses propellant that is solid, and a liquid-propellant rocket uses propellant that is liquid. The propellant provides the engine with thrust, which is the force that actually drives the rocket. The thrust must be greater than the rocket’s weight to propel the rocket upward.

A rocket contains a nozzle at its rear, which allows gases to be released. The nozzle also provides the rocket with the maximum amount of thrust. A nozzle has two components: a throat, which is the narrow part, and an exit cone.

Rockets also have a payload, which is a component that carries cargo. The payload can include astronauts, equipment, a spacecraft, a satellite, and/or a space probe. To launch the payload into either space or orbit, the rocket must first break free from the gravitational pull of Earth. This requires a very high speed, known as escape velocity. To escape the Earth’s gravitational pull, a rocket (or any other spacecraft) must achieve an escape velocity of more than 40,000 kilometers per hour (25,000 miles per hour). Each planet and moon has its own escape velocity.

Early History of Rockets

Rocketry dates back more than two thousand years. Perhaps the first rocket-like device was built around 400 BCE by a Greek named Archytas (ca. 400–350 BCE), who lived in a city that is now in Italy. According to the writings of the Roman Aulus Gellius (ca. 125–ca. 180 CE), Archytas flew a wooden bird that was propelled by steam. Several hundred years later, a Greek named Heron of Alexandria (ca. 10–85 CE) invented his own device, which was also propelled by steam. In the first century CE, the Chinese then began building gunpowder-filled devices that had rocket-like qualities. After experimenting with these devices, the Chinese built devices known as "fire-arrows," which were launched by escaping gas. In 1232, they used these fire-arrows in battle against the Mongols.

Experiments with rockets continued for centuries, particularly in Europe. Rockets eventually began being used for fireworks displays. For example, a sixteenth-century German fireworks maker named Johann Schmidlap invented a rocket that could launch fireworks to higher altitudes than ever before. Known as the "step rocket," Schmidlap’s invention carried two rockets of different sizes into the sky. The larger rocket lifted the device off the ground, and when it was exhausted, the smaller rocket took over, carrying the device to a higher altitude. The step rocket would become the basis for modern-day rockets used for space travel.

Newton’s Laws of Motion

In the late seventeenth century, English scientist Sir Isaac Newton (1642-–1727) developed three scientific laws that would eventually have an impact on rocketry. Commonly referred to as Newton’s laws of motion, the laws were compiled in Newton’s Principia Mathematica Philosophiae Naturalis (1687; trans. 1729). The first law involves an object that is either at rest or moving uniformly. The law states that the object will remain at rest or in uniform motion as long as an external force does not act on the object. This state is known as "inertia."

Newton’s second law addresses the velocity of an object. It states that an external force will change an object’s velocity and that this change is dependent on the force applied (F), the mass of the object (m), and the acceleration of the object (a). The law is often expressed by the following equation:

F = ma

The third law involves action and reaction. The law explains that when one object exerts a force on a second object, the second object will exert an equal but opposite force on the first object. The following statement is commonly used to articulate the law: "For every action, there is an equal and opposite reaction."

Modern Rocketry

Newton’s laws of motion paved the way for modern rocketry. The laws helped improve rocket design and also allowed for larger and more powerful rockets than previously existed. For example, German and Russian rocket experimenters developed rockets that weighed more than forty-five kilograms (one hundred pounds). Rockets were also extremely successful in war. In fact, the lyrics "the rockets’ red glare" in the "Star-Spangled Banner," the national anthem of the United States, were inspired by the rockets used by British ships during the War of 1812.

However, it was not until 1898 that the true potential of rockets was realized. That year, Russian schoolteacher Konstantin Tsiolkovsky (1857–1935) set forth the idea that rockets could be used for space exploration. He published a report in 1903 outlining this idea. Furthermore, rocket experiments by American engineer Robert H. Goddard (1882–1945) in the early twentieth century helped guide rocketry closer to space exploration. It was not long before rocket societies were established throughout the world. Then in 1957, the Soviet Union launched Sputnik I, the world’s first Earth-orbiting artificial satellite. The United States soon followed suit, launching the satellite Explorer I just a few months later. Since then, countless rockets from around the world have been launched into space, and rocketry has continued to evolve.

The Future of Rocket Engines

In 2012, the Orbital Technologies Corporation (ORBITEC), a company based in Madison, Wisconsin, created a new vortex liquid-fuel rocket engine. A traditional liquid rocket engine must have a double wall to protect the combustion chamber from the extreme heat of the burning fuel. Unlike these traditional rocket engines, the vortex liquid-fuel rocket engine does not need a double wall because a different approach is used for the combustion chamber. In a vortex engine, liquid oxygen enters near the base of the chamber, forming a vortex of cold oxygen. This vortex then spirals up the walls of the chamber. Fuel enters the top of the chamber and mixes with the vortex of oxygen at the top, where it combusts, or burns. The burning mixture of oxygen and fuel forms a second vortex that then moves down the center of the chamber, traveling inside the first vortex. Essentially, the first vortex of oxygen is the outer vortex, and the second vortex of the burning mixture is the inner vortex. The reason for this approach is to prevent the walls of the chamber from getting too hot and potentially melting. Being cold oxygen, the outer vortex protects the chamber walls from the direct heat of the burning inner vortex. Therefore, the walls are exposed to only radiant heat, and a double wall is not required. Because these engines do not need a double wall, they are lighter, simpler, and less costly to build than engines that do require a double wall.

In the late 2010s, NASA increasingly began handing over the duties of designing and building new rockets to private aerospace companies. One of those companies, SpaceX, founded by Elon Musk in the early 2000s, handled about two-thirds of NASA’s launches by the year 2020. As of 2022, SpaceX primarily used its Falcon 9 and Falcon Heavy rocket systems for launches. However, the company’s goal has long been to send humans to Mars, and to so that, it developed its Starship launch vehicle. Starship uses a new type of engine named the Raptor, which relies on methane gas for fuel. SpaceX planned to launch its first Starship in late 2022.

PRINCIPAL TERMS

• escape velocity: the speed needed for an object to escape the gravitational pull of a planet or moon. If the object reaches this speed, it will be able to enter outer space.
• Newton’s laws of motion: three scientific laws developed by Isaac Newton that describe an object’s response to a force that acts upon it. These laws relate force, acceleration, mass, and velocity.
• nozzle: an opening at the rear of a rocket that allows gases to be released and accelerates them so that thrust can be maximized.
• payload: the carrying capacity of a rocket, which can include anything from astronauts to a space probe.
• propellant: a mixture of fuel and oxidizer (usually oxygen) that propels a rocket. Both solid and liquid propellants are used in rockets.
• thrust: in rocketry, the force produced by a rocket engine that pushes a rocket upward.

Bibliography

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"Escape Velocity: Fun and Games." NASA. Natl. Aeronautics and Space Administration, 10 Apr. 2009. Web. 28 May 2015.

Hague, Robin. "Vortex." Celestial Mechanics. Robin Hague, 2008. Web. 28 May 2015.

"Newton’s Laws of Motion." NASA. Natl. Aeronautics and Space Administration, 5 May 2015. Web. 28 May 2015.

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"What Is a Rocket?" NASA. Natl. Aeronautics and Space Administration, 21 Sept. 2010. Web. 28 May 2015.