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Thrust-decay time is a term used in rocket engine technology. It is the time (usually in seconds) between engine cut-off as ordered by human or computer guidance input, and the actual complete loss of thrust. Usually engine cut-off is achieved by closing valves that supply propellant to the engine combustion chamber or feed pumps. However, in all practical designs the combustion chamber will still have an amount of propellant in it undergoing the chemical process (or thermal process in the case of nuclear rocket engines) that creates thrust. Thrust decays to zero when chamber pressure is equal to atmospheric pressure (essentially zero in vacuum). Thrust-decay time is not very predictable and can usually only be measured by firing tests of the particular engine.
A rocket engine uses stored rocket propellants as reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust in accordance with Newton's third law. Most rocket engines use the combustion of reactive chemicals to supply the necessary energy, but non-combusting forms such as cold gas thrusters and nuclear thermal rockets also exist. Vehicles propelled by rocket engines are commonly called rockets. Rocket vehicles carry their own oxidizer, unlike most combustion engines, so rocket engines can be used in a vacuum to propel spacecraft and ballistic missiles.
Thrust is a reaction force described quantitatively by Newton's third law. 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. The force applied on a surface in a direction perpendicular or normal to the surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons, and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second. In mechanical engineering, force orthogonal to the main load is referred to as thrust.
A propellant or propellent is a chemical substance used in the production of energy or pressurized gas that is subsequently used to create movement of a fluid or to generate propulsion of a vehicle, projectile, or other object. Common propellants are energetic materials and consist of a fuel like gasoline, jet fuel, rocket fuel, and an oxidizer. Propellants are burned or otherwise decomposed to produce the propellant gas. Other propellants are simply liquids that can readily be vaporized.
Thrust-decay time is of some importance in rocket staging, because long thrust-decay times can cause catastrophic collisions between stages if the next-stage rocket engine experiences thrust variations.
However, thrust-decay time is a critical variable in vertical landings of rocket-powered spacecraft (like the Lunar Module or the DC-X) or aircraft, because in the time between actual touchdown and complete loss of thrust the vehicle is highly unstable and may topple over.
The Apollo Lunar Module, or simply lunar module, originally designated the Lunar Excursion Module (LEM), was the lander spacecraft that was flown from lunar orbit to the Moon's surface during the U.S. Apollo program. It was the first crewed spacecraft to operate exclusively in the airless vacuum of space, and remains the only crewed vehicle to land anywhere beyond Earth.
A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines. In general, jet engines are combustion engines.
A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants (fuel/oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Chinese, Indians, Mongols and Persians, as early as the 13th century.
The expander cycle is a power cycle of a bipropellant rocket engine. In this cycle, the fuel is used to cool the engine's combustion chamber, picking up heat and changing phase. The heated, now gaseous, fuel then powers the turbine that drives the engine's fuel and oxidizer pumps before being injected into the combustion chamber and burned.
RP-1 (alternately, Rocket Propellant-1 or Refined Petroleum-1) is a highly refined form of kerosene outwardly similar to jet fuel, used as rocket fuel. RP-1 has a lower specific impulse than liquid hydrogen (LH2), but is cheaper, stable at room temperature, far less of an explosion hazard, and far denser. RP-1 is significantly more powerful than LH2 by volume. RP-1 also has a fraction of the toxicity and carcinogenic hazards of hydrazine, another room-temperature liquid fuel.
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.
The Aerojet Rocketdyne RS-25, otherwise known as the Space Shuttle main engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle. NASA is planning to continue using the RS-25 on the Space Shuttle's successor, the Space Launch System (SLS).
The J-2 was a liquid-fuel cryogenic rocket engine used on NASA's Saturn IB and Saturn V launch vehicles. Built in the U.S. by Rocketdyne, the J-2 burned cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellants, with each engine producing 1,033.1 kN (232,250 lbf) of thrust in vacuum. The engine's preliminary design dates back to recommendations of the 1959 Silverstein Committee. Rocketdyne won approval to develop the J-2 in June 1960 and the first flight, AS-201, occurred on 26 February 1966. The J-2 underwent several minor upgrades over its operational history to improve the engine's performance, with two major upgrade programs, the de Laval nozzle-type J-2S and aerospike-type J-2T, which were cancelled after the conclusion of the Apollo program.
A rocket engine nozzle is a propelling nozzle used in a rocket engine to expand and accelerate the combustion gases produced by burning propellants so that the exhaust gases exit the nozzle at hypersonic velocities.
Ammonium perchlorate composite propellant (APCP) is a modern solid-propellant rocket used in rocket vehicles. It differs from many traditional solid rocket propellants such as black powder or zinc-sulfur, not only in chemical composition and overall performance, but also by the nature of how it is processed. APCP is cast into shape, as opposed to powder pressing as with black powder. This provides manufacturing regularity and repeatability, which are necessary requirements for use in the aerospace industry.
RD-270 (Russian: Ра́кетный дв́игатель 270, Rocket Engine 270, 8D420) was a single-chamber liquid-bipropellant rocket engine designed by Energomash (USSR) in 1960–1970. It was to be used on the first stages of proposed heavy-lift UR-700 and UR-900 rocket families. It has the highest thrust among single-chamber engines of the USSR, 640 metric tons at the surface of Earth. The propellants used are unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N2O4). The chamber pressure was among the highest considered, being about 26 MPa. This was achieved by applying full-flow staged combustion cycle for all the incoming mass of fuel, which is turned into a gas and passes through a couple of turbines before being burned in the combustion chamber. This allowed the engine to achieve a specific impulse of 301 s (2.95 km/s) at the Earth's surface.
This article briefly describes the components and systems found in jet engines.
The Titan II GLV or Gemini-Titan II was an American expendable launch system derived from the Titan II missile, which was used to launch twelve Gemini missions for NASA between 1964 and 1966. Two uncrewed launches followed by ten crewed ones were conducted from Launch Complex 19 at the Cape Canaveral Air Force Station, starting with Gemini 1 on April 8, 1964.
A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel or oxidizer, that is, its fuel or oxidizer are gases liquefied and stored at very low temperatures. These highly efficient engines were first flown on the US Atlas-Centaur and were one of the main factors of NASA's success in reaching the Moon by the Saturn V rocket.
Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines.
A liquid apogee engine (LAE), or apogee engine, refers to a type of chemical rocket engine typically used as the main engine in a spacecraft.
Rutherford is a liquid-propellant rocket engine designed by American-New Zealand aerospace company Rocket Lab and manufactured in California. It uses LOX and RP-1 as its propellants and is the first flight-ready engine to use the electric-pump feed cycle. It is used on the company's own rocket, Electron. The rocket uses a similar engine arrangement to the Falcon 9; a two-stage rocket using a cluster of nine identical engines on the first stage, and one vacuum-optimized version with a longer nozzle on the second stage. The sea-level version produces 24 kN (5,400 lbf) of thrust and has a specific impulse of 311 s (3.05 km/s), while the vacuum optimized-version produces 24 kN (5,400 lbf) of thrust and has a specific impulse of 343 s (3.36 km/s).
Zefiro is a family of solid-fuel rocket motor developed by Avio and used on the European Space Agency Vega rocket. The name Zefiro derives from the acronym ZEro FIrst stage ROcket, conceived when this motor was intended to be used as first and second stages of San Marco program of the Italian Space Agency. After its intended use as booster was shelved the acronym was dropped and only the reference to the Greek god of the west wind Zephyrus remained.