Liquid propellant engine

A liquid-propellant rocket or liquid rocket is a rocket engine that uses liquid propellants. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight centrifugal turbopumps to pump the propellant from the tanks into the combustion chamber, which means that the propellants can be kept under low pressure. This permits the use of low-mass propellant tanks, resulting in a high mass ratio for the rocket.

An inert gas stored in a tank at a high pressure is sometimes used instead of pumps in simpler small engines to force the propellants into the combustion chamber. These engines may have a lower mass ratio, but are usually more reliable. and are therefore used widely in satellites for orbit maintenance.

Liquid rockets can be monopropellant rockets using a single type of propellant, bipropellant rockets using two types of propellant, or more exotic tripropellant rockets using three types of propellant. Some designs are throttleable for variable thrust operation and some may be restarted after a previous in-space shutdown. Liquid propellants are also used in hybrid rockets, in which a liquid oxidizer is generally combined with a solid fuel.

The idea of liquid rocket as understood in the modern context first appears in the book The Exploration of Cosmic Space by Means of Reaction Devices, by the Russian school teacher Konstantin Tsiolkovsky. This seminal treatise on astronautics was published in 1903, but was not distributed outside Russia until years later, and Russian scientists paid little attention to it.

Pedro Eleodoro Paulet Mostajo (July 2, 1874 – January 30, 1945) was a Peruvian scientist & inventor who allegedly in 1895 was the first person to build a liquid-fuel rocket engine and, in 1900, the first person to build a modern rocket propulsion system.[1] German V-2 inventor Wernher von Braun considered Paulet one of the "fathers of aeronautics." The National Air & Space Museum in Washington, D.C., has a small plaque honoring the memory of Paulet. He was the only known developer of liquid-propellant rocket engine experiments in the 19th century, considered one of the "fathers of aeronautics.". However, he did not publish his work. In 1927 he wrote a letter to a newspaper in Lima, claiming he had experimented with a liquid rocket engine while he was a student in Paris three decades earlier. Historians of early rocketry experiments, among them Max Valier, Willy Ley, and John D. Clark, have given differing amounts of credence to Paulet's report. Paulet described laboratory tests of, but did not claim to have launched a liquid rocket. Wernher von Braun, in his book World History of Aeronautics states: "Pedro Paulet was in Paris in those years (1900), experimenting with his tiny two-and-a-half kilogram motor, and achieved 100 kg of force. By this act, Paulet should be considered the pioneer of the liquid fuel propulsion motor." Further, in his History of Rocketry and Space Travel, von Braun recognizes that "by his efforts, Paulet helped man reach the Moon."[3]

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