Modern liquid fuel rockets operate on a very similar design concept to Goddard's, with the main three parts of the engine still consisting of a fuel tank, an oxidizer tank, and a combustion chamber. However, modern systems often incorporate far more sophisticated machinery, and are built to much higher levels of precision to handle modern standards of efficiency. One specific adaptation has been the introduction of liquid hydrogen as the main source of fuel. Liquid hydrogen is much, much colder than the liquid oxygen and gasoline used in Goddard’s time, and thus modern engines need more advanced systems of lubrication, fuel storage (which has to be directly next to the engine to avoid evaporation), and temperature control between the extremely cold fuel and the incredibly hot combustion chamber.
Another important consideration that has emerged is the physical size and weight of engine components. Since Goddard's era, a major limitation on rocket efficiency has been that much of a rocket's weight and bulk comes from the large number of individual parts within the engine itself and other machinery. As a result, many modern rocket engineers aim to reduce both the size and weight of these components, thus increasing the thrust to weight ratio and producing higher acceleration. Achieving this requires exceptionally high precision in both manufacturing and assembly, a level of detail that was not as critical during Goddard's time.
Finally, modern rockets also have to be engineered to meet modern environmental efficiency standards, and also be cost effective. Liquid hydrogen, methane and kerosene are used instead of gasoline because they are more design efficient, more chemically efficient, and burn much cleaner than the other alternatives.
Liquid (Cryogenic) Hydrogen is most effective (High Specific Impulse) in the space environment, where efficiency is most important, but not so much in the initial launch stages when raw power is needed to get the mass moving. Therefore, solid fuels or other liquid fuel options are used more commonly in booster engines.
Illustration by Encyclopedia Britannica
https://www.britannica.com/technology/rocket-jet-propulsion-device-and-vehicle/Liquid-propellant-rocket-engines
Understanding Question:
Visit the link https://techsight.co/index.php/2021/06/24/raptor-rocket-engine-animated-schematic-infographic/
And look at the diagram above, both depicting schematics for modern liquid fuel engines, and describe how they are similar and/or different to Goddard’s model.
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Now we will look at some specific examples of modern rocket engines:
RL10 Engine:
The RL10 engine was created in 1959, and uses liquid hydrogen as fuel, and has been widely used by satellite launching systems. Many versions of this engine have been produced since 1959, with the RL10B-2 engine current in development projected to be the most efficient of any modern rocket engine, with a specific impulse of over 400 seconds. Learn more about specific impulse in our Rocketry Math lesson.
Gerondidakis, D. (2016). Commercial Crew Program (CCP) Astronauts visit Aerojet Rocketdyne. photograph, West Palm Beach. images-assets.nasa.gov/image/KSC-20160812-PH_DNG01_0078/KSC-20160812-PH_DNG01_0078~orig.JPG
RD-180 Engine:
The RD-180 engine, developed by NPO Energomash and modified by Pratt and Whitney, is a booster engine used to get rockets off the ground that uses liquid fuel (Kerosene). It is able to provide almost 1 million pounds of thrust (Goddard's rockets, remember, could provide around 160,000 lbs), while being much smaller and more manageable than earlier similar prototypes.
Raptor Engine:
The Raptor Engine is a modern, energy efficient liquid fuel engine developed by SpaceX. It uses methane as fuel, which burns cleaner than kerosene, is less prone to fatal explosions, and can also be produced on Mars, which is important for SpaceX’s goal of humankind walking on Mars. Finally, it is designed to be reusable for multiple flights, and thus could be sent back and forth from a planet like Mars.
What makes this engine so revolutionary is that it is made entirely through 3d printing processes. There are three generations of this engine, with Raptor 3 featuring nearly all of its piping and channels 3D-printed directly into the engine’s structure. This design makes the engine look remarkably simple from the outside, even though it remains highly complex internally. This sort of 3d printing technology has begun to be tested on even large scales, including building new parts for the International Space Station, and could revolutionize space-based manufacturing in the near future.
