LIQUID ROCKET

A 'liquid rocket' is a rocket with an engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume and hence the mass of the tankage to be relatively low, resulting in a high mass ratio. Liquid rockets have been built as 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. Bipropellant liquid rockets generally use one liquid fuel and one oxidizer, such as liquid hydrogen and liquid oxygen. Liquid propellants are also sometimes used in hybrid rockets, in which they are combined with a solid or gaseous propellant.

Contents

History

Advantages of liquid rockets

Disadvantages of liquid rockets

References

See also

External links

History

The idea of liquid fuel rocket as understood in the modern context first appears in the book Исследование мировых пространств реактивными приборами (Romanisation: Issledovanie mirovh
prostranst[o]v)
(The Exploration of Cosmic Space by Means of Reaction Devices), by Konstantin Eduardovitch Tsiolkovsky. This seminal treatise on astronautics was published in 1903.
The only known claim to liquid propellant rocket engine experiments in the nineteenth century was made by Pedro Paulet, a Peruvian scientist.^[1]
However, he did not immediately 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 and Willy Ley, have given differing amounts of credence to Paulet's report. Paulet described laboratory tests of liquid rocket engines, but did not claim to have flown a liquid rocket.
The first flight of a vehicle powered by a liquid-rocket took place on March 16, 1926 at Auburn, Massachusetts, when American professor Robert H. Goddard launched a rocket which used liquid oxygen and gasoline as propellants.^[2] The rocket, which was dubbed "Nell", rose just 41 feet during a 2.5-second flight that ended in a cabbage field, but it was an important demonstration that liquid-fueled rockets were possible.

Advantages of liquid rockets

Unlike gases, a typical liquid propellant has a density similar to water, approximately 0.7-1.4g/cm³ (except liquid hydrogen which has a very much lower density), while requiring only relatively modest pressuristation to prevent vapourisation. This combination of density and low pressure permits very lightweight tankage; approximately 1% of the contents for dense propellants and around 10% for liquid hydrogen (due to its low density and the mass of the required insulation).
For injection into the combustion chamber the propellant pressure needs to be greater than the chamber pressure at the injectors; this is can be achieved with a pump. Suitable pumps usually use turbopumps due to their high power and lightweight, although reciprocating pumps have been employed in the past. Turbopumps are usually extremely lightweight and can give excellent performance.
Alternatively, a heavy tank can be used, and the pump foregone; but the delta-v that the stage can achieve is much lower.

Disadvantages of liquid rockets

Liquid propellants can cause a number of issues:

★ because the propellant is a very large proportion of the mass of the vehicle, the center of mass shifts significantly rearward as the propellant is used; it is important that the center of mass not get too close to the center of drag of the vehicle, otherwise loss of control normally occurs.

★ liquid propellants are subject to ''slosh'', which has frequently lead to loss of control of the vehicle

★ liquid propellants can leak, possibly leading to an explosive mixture forming

★ turbopumps to pump liquid propellants are complex to design, and can suffer serious failure modes, such as overspeeding if they run dry or shedding fragments at high speed if metal particles from the manufacturing process enter the pump

★ propellants are subject to vortexing within the tank, particularly towards the end of the burn, which can result in gas being sucked into the engine or pump

★ cryogenic propellants, such as liquid oxygen freezes atmospheric water vapour into very hard crystals. This can damage or block seals and valves and can cause leaks and other failures. Avoidance of this problem often requires lengthy ''chilldown'' procedures which attempts to remove as much of the vapour from the system as possible.

★ cryogenic propellants can cause ice to form on the outside of the tank, this can fall and damage the vehicle itself.

References

1.
The alleged contributions of Pedro E. Paulet to liquid-propellant rocketry
2.
Re-Creating History

See also

★ Solid rocket

★ Liquid rocket propellants

External links

★ An online book entitled ''”How to Design, Build, and Test Small Liquid-Fuel Rocket Engines”''