Hot Water Rocket
Encyclopedia
A steam rocket is a thermal rocket
Thermal rocket
A thermal rocket is a rocket engine that uses a propellant that is externally heated before being passed through a nozzle, as opposed to undergoing a chemical reaction as in a chemical rocket.Thermal rockets can give high performance....

 that uses water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 held in a pressure vessel
Pressure vessel
A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design,...

 at a high temperature, such that its saturated vapor pressure is significantly greater than ambient pressure. The water is allowed to escape as steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

 through a rocket nozzle to produce thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

.

Steam rockets are probably best known for their use in rocket-powered car and bikes, and they are the type used in aeolipile
Aeolipile
An aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the 1st century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile Hero described is considered to be the first recorded steam engine...

.

Steam rockets are usually pressure fed, but more complex designs using solar energy
Solar thermal rocket
Solar thermal propulsion is a form of spacecraft propulsion that makes use of solar power to directly heat reaction mass, and therefore does not require an electrical generator as most other forms of solar-powered propulsion do. A solar thermal rocket only has to carry the means of capturing solar...

 or nuclear energy
Nuclear thermal rocket
In a nuclear thermal rocket a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle to create thrust. In this kind of thermal rocket, the nuclear reactor's energy replaces the chemical energy of the propellant's...

 have been proposed.

Principle of operation

Water, while under pressure, is heated up to a high temperature (approx. 250-500 °C). As the hot water goes through the nozzle (usually a de Laval nozzle
De Laval nozzle
A de Laval nozzle is a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass-shape...

) and the pressure reduces, the water flashes to steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

 pressing on the nozzle, and leaving at high speed. By the recoil the rocket accelerates in the opposite direction to the steam. The nozzle of hot water rockets must be able to withstand high pressure, high temperatures and the particularly corrosive nature of hot water.

The simplest design has a pressurised water tank where the water is heated before launch, however, this gives a very low exhaust velocity since the high latent heat of vapourisation means that very little actual steam is produced and the exhaust consists mostly of water, or if high temperatures and pressures are used, then the tank is very heavy.

More complex designs can involve passing the water through pumps and heat exchangers and employing nuclear reactors or solar heating, it is estimated that these can give a specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

 of over 195 s Isp, still below the up to 465 s a modern hydrogen engines deliver (Vinci
Vinci (rocket engine)
Vinci is a European Space Agency cryogenic rocket engine currently under development. It is designed to power the new upper stage of Ariane 5, ESC-B, and will be the first European re-ignitable cryogenic upper stage engine, raising the launcher's GTO performances to 12 t.-Overview:Vinci is an...

).

Applications of steam rockets

  • An aeolipile
    Aeolipile
    An aeolipile , also known as a Hero engine, is a rocket style jet engine which spins when heated. In the 1st century AD, Hero of Alexandria described the device, and many sources give him the credit for its invention.The aeolipile Hero described is considered to be the first recorded steam engine...

     is pushed around by steam rockets
  • Evel Knievel
    Evel Knievel
    Evel Knievel , born Robert Craig Knievel, was an American daredevil and entertainer. In his career he attempted over 75 ramp-to-ramp motorcycle jumps between 1965 and 1980, and in 1974, a failed jump across Snake River Canyon in the Skycycle X-2, a steam-powered rocket...

    's Skycycle X-2 used for the Snake River Canyon jump used a steam rocket designed by Robert Truax
    Robert Truax
    Captain Robert C. Truax was a rocket engineer in the United States Navy, and companies such as Aerojet and Truax Engineering, which he founded...

  • Art Arfons
    Art Arfons
    Arthur Eugene "Art" Arfons was the world land speed record holder three times in 1964 – 1965 with his Green Monster series of jet-powered cars, after a series of Green Monster piston-engine and jet-engined dragsters...

    's "Neptune I" dragster, also used a steam rocket designed by Robert Truax
  • Hot water rockets are used occasionally as auxiliary launch aids and for experimentation purposes..

Proposed uses of steam rockets

Solar or nuclear heated steam rockets have been proposed for use in interplanetary travel. Although the performance is low, high mass fraction
Mass fraction
In aerospace engineering, the propellant mass fraction is a measure of a vehicle's performance, determined as the portion of the vehicle's mass which does not reach the destination...

s are easy to achieve, and water is expected to be very easy to extract and purify from ice deposits that are found around the solar system.

Popular culture

Steam rocket have occasionally appeared in science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 novels.
  • Steamboy
    Steamboy
    is a 2004 Japanese animated steampunk film, produced by Sunrise, and directed and co-written by Katsuhiro Otomo, his second major anime release, following Akira. The film was released in Japan on July 17, 2004. Steamboy is the most expensive full length Japanese animated movie made to date...


External links

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