The easy start and restart capability of hypergols make them ideal for spacecraft maneuvering systems. Also, since hypergols remain liquid at normal temperatures, they do not pose the storage problems of cryogenic propellants. Hypergols are highly toxic and must be handled with extreme care. Hydrazine gives the best performance as a rocket fuel, but it has a high freezing point and is too unstable for use as a coolant. MMH is more stable and gives the best performance when freezing point is an issue, such as spacecraft propulsion applications.
UDMH has the lowest freezing point and has enough thermal stability to be used in large regeneratively cooled engines. Consequently, UDMH is often used in launch vehicle applications even though it is the least efficient of the hydrazine derivatives.
Aerozine 50 is almost as stable as UDMH and provides better performance. The oxidizer is usually nitrogen tetroxide NTO or nitric acid. Nitrogen tetroxide is less corrosive than nitric acid and provides better performance, but it has a higher freezing point. Consequently, nitrogen tetroxide is usually the oxidizer of choice when freezing point is not an issue, however, the freezing point can be lowered with the introduction nitric oxide.
The resulting oxidizer is called mixed oxides of nitrogen MON. The number included in the description, e. Hydrazine is also frequently used as a monopropellant in catalytic decomposition engines. In these engines, a liquid fuel decomposes into hot gas in the presence of a catalyst. The decomposition of hydrazine produces temperatures up to about 1, o C 2, o F and a specific impulse of about or seconds.
Hydrazine decomposes to either hydrogen and nitrogen, or ammonia and nitrogen. Other propellants have also been used, a few of which deserve mentioning: Alcohols were commonly used as fuels during the early years of rocketry.
However, as more efficient fuels where developed, alcohols fell into general disuse. Hydrogen peroxide once attracted considerable attention as an oxidizer and was used in Britain's Black Arrow rocket. In high concentrations, hydrogen peroxide is called high-test peroxide HTP. The performance and density of HTP is close to that of nitric acid, and it is far less toxic and corrosive; however it has a poor freezing point and is unstable. Although HTP never made it as an oxidizer in large bi-propellant applications, it has found widespread use as a monopropellant.
In the presence of a catalyst, HTP decomposes into oxygen and superheated steam and produces a specific impulse of about s. Nitrous oxide has been used as both an oxidizer and as a monopropellant.
It is the oxidizer of choice for many hybrid rocket designs and has been used frequently in amateur high-powered rocketry. In the presence of a catalyst, nitrous oxide will decompose exothermically into nitrogen and oxygen and produce a specific impulse of about s. Solid Propellants.
Solid propellant motors are the simplest of all rocket designs. They consist of a casing, usually steel, filled with a mixture of solid compounds fuel and oxidizer that burn at a rapid rate, expelling hot gases from a nozzle to produce thrust. When ignited, a solid propellant burns from the center out towards the sides of the casing. The shape of the center channel determines the rate and pattern of the burn, thus providing a means to control thrust.
Unlike liquid propellant engines, solid propellant motors cannot be shut down. Once ignited, they will burn until all the propellant is exhausted. There are two families of solids propellants: homogeneous and composite.
Both types are dense, stable at ordinary temperatures, and easily storable. Homogeneous propellants are either simple base or double base. In a black powder rocket the fuel is carbon and the oxidant, potassium nitrate. Sulphur acts as a secondary fuel and also catalyses the reaction.
In the Ariane 5 solid fuel boosters the fuel is aluminium powder, the oxidant, ammonium perchlorate and polybutadiene acts as a binder to hold the mixture together.
Until the early 20th century rocket motors were never more than a few percent efficient. The problem is that a simple rocket uses only the pressure difference between the combustion chamber and the ambient pressure outside to drive the rocket forward: The result is that huge amounts of high pressure, high temperature exhaust is thrown out but that it carries with it massive amounts of energy in the form of gas pressure and heat.
The main engines are more likely to be propelled by liquid fuel. Liquid fuel engines are composed of liquid oxygen and liquid hydrogen. The liquid hydrogen is the fuel and the liquid oxygen is the oxidizer. Remember, the oxidizer helps the fuel burn. The hydrogen needs to be in liquid form, not gas form, in order to have a smaller tank on the rocket.
Gasses are lightweight, so it would take a larger tank to hold hydrogen gas than it would be to hold liquid hydrogen. The liquid hydrogen and oxygen are released into an engine where they begin to combine to make water. Just like the solid fuel, the water vapor creates energy and steam.
The steam is released to make the rocket go upwards. To get a rocket from the ground into space, rockets need both solid fuel and liquid fuel. You would think that rockets could just carry liquid fuel because liquid fuel is more efficient and gives more push when burned.
However, having only liquid fuel would require a huge tank of fuel.
0コメント