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A rocket is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellants carried within the rocket before use.[1] Rocket engines work by action and reaction. Rocket engines push rockets forward simply by throwing their exhaust backwards extremely fast.
While comparatively inefficient for low speed use, rockets are relatively lightweight and powerful, capable of generating large accelerations and of attaining extremely high speeds with reasonable efficiency. Rockets are not reliant on the atmosphere and work very well in space.
Rockets for military and recreational uses date back to at least 13th century China.[2] Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology for the Space Age, including setting foot on the moon. Rockets are now used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight, and space exploration.
Chemical rockets are the most common type of high performance rocket and they typically create their exhaust by the combustion of rocket propellant. Chemical rockets store a large amount of energy in an easily released form, and can be very dangerous. However, careful design, testing, construction and use minimizes risks.
The availability of black powder (gunpowder) to propel projectiles was a precursor to experiments as weapons such as bombs, cannon, incendiary fire arrows and rocket-propelled fire arrows.[nb 1][nb 2] The discovery of gunpowder was probably the product of centuries of alchemical experimentation in which Taoist alchemists were trying to create an elixir of immortality that would allow the person ingesting it to become physically immortal.[5] However, anyone with a wood fire might have observed the acceleration of combustion that accidentally-chosen saltpetre-containing rocks would have produced.
Exactly when the first flights of rockets occurred is contested. Merely lighting a centimeter-sized solid lump of gunpowder on one side can cause it to move via reaction (even without a nozzle for efficiency), so confinement in a tube and other design refinements may easily have followed for the experimentally-minded with ready access to saltpetre.
A problem for dating the first rocket flight is that Chinese fire arrows can be either arrows with explosives attached, or arrows propelled by gunpowder. There were reports of fire arrows and 'iron pots' that could be heard for 5 leagues (25 km, or 15 miles) when they exploded, causing devastation for a radius of 600 meters (2,000 feet), apparently due to shrapnel.[6] A common claim is that the first recorded use of a rocket in battle was by the Chinese in 1232 against the Mongol hordes at Kai Feng Fu.[7] However, the lowering of iron pots there may have been a way for a besieged army to blow up invaders.[nb 3] A scholarly reference occurs in the Ko Chieh Ching Yuan (The Mirror of Research), states that in 998 AD a man named Tang Fu invented a fire arrow of a new kind having an iron head.[7]
Less controversially, one of the earliest devices recorded that used internal-combustion rocket propulsion, was the 'ground-rat,' a type of firework recorded in 1264 as having frightened the Empress-Mother Kung Sheng at a feast held in her honor by her son the Emperor Lizong.[9]
Subsequently, one of the earliest texts to mention the use of rockets was the Huolongjing, written by the Chinese artillery officer Jiao Yu in the mid-14th century. This text also mentioned the use of the first known multistage rocket, the 'fire-dragon issuing from the water' (huo long chu shui), used mostly by the Chinese navy.[10]
Rocket technology was first known to Europeans following its use by the Mongols Genghis Khan and Ögedei Khan when they conquered parts of Russia, Eastern, and Central Europe. The Mongolians had acquired the Chinese technology by conquest of the northern part of China and by the subsequent employment of Chinese rocketry experts as mercenaries for the Mongol military. Reports of the Battle of Mohi in the year 1241 describe the use of rocket-like weapons by the Mongols against the Magyars.[6] Rocket technology also spread to Korea, with the 15th century wheeled hwacha that would launch singijeon rockets.[citation needed] Additionally, the spread of rockets into Europe was also influenced by the Ottomans at the siege of Constantinople in 1453, although it is very likely that the Ottomans themselves were influenced by the Mongol invasions of the previous few centuries. In their history of rockets published on the Internet, NASA says "Rockets appear in Arab literature in 1258 A.D., describing Mongol invaders' use of them on February 15 to capture the city of Baghdad."[6]
Between 1270 and 1280, Hasan al-Rammah wrote al-furusiyyah wa al-manasib al-harbiyya (The Book of Military Horsemanship and Ingenious War Devices), which included 107 gunpowder recipes, 22 of which are for rockets.[11] According to Ahmad Y Hassan, al-Rammah's recipes were more explosive than rockets used in China at the time.[12][unreliable source?] The terminology used by al-Rammah indicated a Chinese origin for the gunpowder weapons he wrote about, such as rockets and fire lances.[13] Ibn al-Baytar, an Arab from Spain who had immigrated to Egypt, gave the name "snow of China" (Arabic: ثلج الصين thalj al-Sin) to describe saltpetre. Al-Baytar died in 1248.[14][15] The earlier Arab historians call saltpeter "Chinese snow" and " Chinese salt;" [16][17] The Arabs also used the name "Chinese arrows" to refer to rockets.[18][19][20][21][22][23][24] The Arabs attached "Chinese" to various names for gunpowder related objects. "Chinese flowers" was the name for fireworks, while "Chinese Snow" was given to saltpeter and "Chinese arrows" to rockets.[13] While saltpeter was called "Chinese Snow" by Arabs, it was called "Chinese salt" by the Iranians/Persians.[25][26][27][28][29]
The name Rocket comes from the Italian Rocchetta (i.e. little fuse), a name of a small firecracker created by the Italian artificer Muratori in 1379.[30]
Konrad Kyeser described rockets in his famous military treatise Bellifortis around 1405.[31]
Between 1529 and 1556 Conrad Haas wrote a book that described rocket technology that combined fireworks and weapons technologies. This manuscript was discovered in 1961, in the Sibiu public records (Sibiu public records Varia II 374). His work dealt with the theory of motion of multi-stage rockets, different fuel mixtures using liquid fuel, and introduced delta-shape fins and bell-shaped nozzles.[32]
Lagari Hasan Çelebi was a legendary Ottoman aviator who, according to an account written by Evliya Çelebi, made a successful manned rocket flight. Evliya Çelebi purported that in 1633 Lagari Hasan Çelebi launched in a 7-winged rocket using 50 okka (140 lbs) of gunpowder from Sarayburnu, the point below Topkapı Palace in Istanbul.
For over two centuries, the work of Polish-Lithuanian Commonwealth nobleman Kazimierz Siemienowicz "Artis Magnae Artilleriae pars prima" ("Great Art of Artillery, the First Part", also known as "The Complete Art of Artillery"), was used in Europe as a basic artillery manual.[33] First printed in Amsterdam in 1650 it was translated to French in 1651, German in 1676, English and Dutch in 1729 and Polish in 1963. The book provided the standard designs for creating rockets, fireballs, and other pyrotechnic devices. It contained a large chapter on caliber, construction, production and properties of rockets (for both military and civil purposes), including multi-stage rockets, batteries of rockets, and rockets with delta wing stabilizers (instead of the common guiding rods ("bottle rockets"), which are also aerodynamic stabilizers but less efficient than fins).
In 1792, the first iron-cased rockets were successfully developed and used by Hyder Ali and his son Tipu Sultan, rulers of the Kingdom of Mysore in India against the larger British East India Company forces during the Anglo-Mysore Wars. The British then took an active interest in the technology and developed it further during the 19th century. The Mysore rockets of this period were much more advanced than the British had previously seen, chiefly because of the use of iron tubes for holding the propellant; this enabled higher thrust and longer range for the missile (up to 2 km range). After Tipu's eventual defeat in the Fourth Anglo-Mysore War and the capture of the Mysore iron rockets, they were influential in British rocket development, inspiring the Congreve rocket, which was soon put into use in the Napoleonic Wars.[34]
William Congreve, son of the Comptroller of the Royal Arsenal, Woolwich, London, became a major figure in the field. From 1801, Congreve researched on the original design of Mysore rockets and set on a vigorous development program at the Arsenal's laboratory.[35] Congreve prepared a new propellant mixture, and developed a rocket motor with a strong iron tube with conical nose. This early Congreve rocket weighed about 32 pounds (14.5 kilograms). The Royal Arsenal's first demonstration of solid fuel rockets was in 1805. The rockets were effectively used during the Napoleonic Wars and the War of 1812. Congreve published three books on rocketry.[36]
From there, the use of military rockets spread throughout the western world. At the Battle of Baltimore in 1814, the rockets fired on Fort McHenry by the rocket vessel HMS Erebus were the source of the rockets' red glare described by Francis Scott Key in The Star-Spangled Banner.[37] Rockets were also used in the Battle of Waterloo.[38]
Early rockets were very inaccurate. Without the use of spinning or any gimballing of the thrust, they had a strong tendency to veer sharply off of their intended course. The early Mysorean rockets and their successor British Congreve rockets[35] reduced this somewhat by attaching a long stick to the end of a rocket (similar to modern bottle rockets) to make it harder for the rocket to change course. The largest of the Congreve rockets was the 32-pound (14.5 kg) Carcass, which had a 15-foot (4.6 m) stick. Originally, sticks were mounted on the side, but this was later changed to mounting in the center of the rocket, reducing drag and enabling the rocket to be more accurately fired from a segment of pipe.
The accuracy problem was greatly improved in 1844 when William Hale[39] modified the rocket design so that thrust was slightly vectored, causing the rocket to spin along its axis of travel like a bullet. The Hale rocket removed the need for a rocket stick, travelled further due to reduced air resistance, and was far more accurate.
In 1865 the British Colonel Edward Mounier Boxer built an improved versione of the Congreve rocket placing two rockets in one tube, one behind the other.[40]
At the beginning of the 20th Century, there was a burst of scientific investigation into interplanetary travel, largely driven by the inspiration of fiction by writers such as Jules Verne and H.G.Wells. Scientists seized on the rocket as a technology that was able to achieve this in real life.
In 1903, high school mathematics teacher Konstantin Tsiolkovsky (1857–1935), published Исследование мировых пространств реактивными приборами[41] (The Exploration of Cosmic Space by Means of Reaction Devices), the first serious scientific work on space travel. The Tsiolkovsky rocket equation—the principle that governs rocket propulsion—is named in his honor (although it had been discovered previously).[42] He also advocated the use of liquid hydrogen and oxygen for propellant, calculating their maximum exhaust velocity. His work was essentially unknown outside the Soviet Union, but inside the country it inspired further research, experimentation and the formation of the Society for Studies of Interplanetary Travel in 1924.
In 1912, Robert Esnault-Pelterie published a lecture[43] on rocket theory and interplanetary travel. He independently derived Tsiolkovsky's rocket equation, did basic calculations about the energy required to make round trips to the Moon and planets, and he proposed the use of atomic power (i.e. Radium) to power a jet drive.
In 1912 Robert Goddard, inspired from an early age by H.G.Wells, began a serious analysis of rockets, concluding that conventional solid-fuel rockets needed to be improved in three ways. First, fuel should be burned in a small combustion chamber, instead of building the entire propellant container to withstand the high pressures. Second, rockets could be arranged in stages. Finally, the exhaust speed (and thus the efficiency) could be greatly increased to beyond the speed of sound by using a De Laval nozzle. He patented these concepts in 1914.[44] He also independently developed the mathematics of rocket flight.
In 1920, Goddard published these ideas and experimental results in A Method of Reaching Extreme Altitudes.[45] The work included remarks about sending a solid-fuel rocket to the Moon, which attracted worldwide attention and was both praised and ridiculed. A New York Times editorial suggested:
—New York Times, 13 January 1920[46]
In 1923, Hermann Oberth (1894–1989) published Die Rakete zu den Planetenräumen ("The Rocket into Planetary Space"), a version of his doctoral thesis, after the University of Munich rejected it.[47]
In 1924, Tsiolkovsky also wrote about multi-stage rockets, in 'Cosmic Rocket Trains'[48]
Modern rockets were born when Goddard attached a supersonic (de Laval) nozzle to a liquid-fueled rocket engine's combustion chamber. These nozzles turn the hot gas from the combustion chamber into a cooler, hypersonic, highly directed jet of gas, more than doubling the thrust and raising the engine efficiency from 2% to 64%.[49][50] In 1926, Robert Goddard launched the world's first liquid-fueled rocket in Auburn, Massachusetts.
During the 1920s, a number of rocket research organizations appeared worldwide. In 1927 the German car manufacturer Opel began to research rocket vehicles together with Mark Valier and the solid-fuel rocket builder Friedrich Wilhelm Sander.[51] In 1928, Fritz von Opel drove with a rocket car, the Opel-RAK.1 on the Opel raceway in Rüsselsheim, Germany. In 1928 the Lippisch Ente flew, rocket power was used to launch the manned glider, although it was destroyed on its second flight. In 1929 von Opel started at the Frankfurt-Rebstock airport with the Opel-Sander RAK 1-airplane, which was damaged beyond repair during a hard landing after its first flight.
In the mid-1920s, German scientists had begun experimenting with rockets that used liquid propellants capable of reaching relatively high altitudes and distances. In 1927 and also in Germany, a team of amateur rocket engineers had formed the Verein für Raumschiffahrt (German Rocket Society, or VfR), and in 1931 launched a liquid propellant rocket (using oxygen and gasoline).[52]
From 1931 to 1937 in Russia, extensive scientific work on rocket engine design occurred in Leningrad at the Gas Dynamics Laboratory there. Well-funded and staffed, over 100 experimental engines were built under the direction of Valentin Glushko. The work included regenerative cooling, hypergolic propellant ignition, and fuel injector designs that included swirling and bi-propellant mixing injectors. However, the work was curtailed by Glushko's arrest during Stalinist purges in 1938. Similar work was also done by the Austrian professor Eugen Sänger who worked on rocket-powered spaceplanes such as Silbervogel (sometimes called the 'antipodal' bomber.)[53]
On November 12, 1932 at a farm in Stockton NJ, the American Interplanetary Society's attempt to static fire their first rocket (based on German Rocket Society designs) failed in a fire.[54]
In 1930s, the Reichswehr (which in 1935 became the Wehrmacht) began to take an interest in rocketry.[55] Artillery restrictions imposed by the Treaty of Versailles limited Germany's access to long distance weaponry. Seeing the possibility of using rockets as long-range artillery fire, the Wehrmacht initially funded the VfR team, but because their focus was strictly scientific, created its own research team. At the behest of military leaders, Wernher von Braun, at the time a young aspiring rocket scientist, joined the military (followed by two former VfR members) and developed long-range weapons for use in World War II by Nazi Germany.[56]
In 1943, production of the V-2 rocket began in Germany. It had an operational range of 300 km (190 mi) and carried a 1,000 kg (2,200 lb) warhead, with an amatol explosive charge. It normally achieved an operational maximum altitude of around 90 km (56 mi), but could achieve 206 km (128 mi) if launched vertically. The vehicle was similar to most modern rockets, with turbopumps, inertial guidance and many other features. Thousands were fired at various Allied nations, mainly Belgium, as well as England and France. While they could not be intercepted, their guidance system design and single conventional warhead meant that it was insufficiently accurate against military targets. A total of 2,754 people in England were killed, and 6,523 were wounded before the launch campaign was ended. There were also 20,000 deaths of slave labour during the construction of V-2s. While it did not significantly affect the course of the war, the V-2 provided a lethal demonstration of the potential for guided rockets as weapons.[57][58]
In parallel with the guided missile programme in Nazi Germany, rockets were also used on aircraft, either for assisting horizontal take-off (JATO), vertical take-off (Bachem Ba 349 "Natter") or for powering them (Me 163,[59] etc.). During the war Germany also developed several guided and unguided air-to-air, ground-to-air and ground-to-ground missiles (see list of World War II guided missiles of Germany).
The Allies rocket programs were much less sophisticated, relying mostly on unguided missiles like the Soviet Katyusha rocket.
At the end of World War II, competing Russian, British, and US military and scientific crews raced to capture technology and trained personnel from the German rocket program at Peenemünde. Russia and Britain had some success, but the United States benefited the most. The US captured a large number of German rocket scientists, including von Braun, and brought them to the United States as part of Operation Overcast.[60] In America, the same rockets that were designed to rain down on Britain were used instead by scientists as research vehicles for developing the new technology further. The V-2 evolved into the American Redstone rocket, used in the early space program.[61]
After the war, rockets were used to study high-altitude conditions, by radio telemetry of temperature and pressure of the atmosphere, detection of cosmic rays, and further research; notably for the Bell X-1 to break the sound barrier. This continued in the US under von Braun and the others, who were destined to become part of the US scientific community.
Independently, in the Soviet Union's space program research continued under the leadership of the chief designer Sergei Korolev.[62] With the help of German technicians, the V-2 was duplicated and improved as the R-1, R-2 and R-5 missiles. German designs were abandoned in the late 1940s, and the foreign workers were sent home. A new series of engines built by Glushko and based on inventions of Aleksei Mihailovich Isaev formed the basis of the first ICBM, the R-7.[63] The R-7 launched the first satellite- Sputnik 1, and later Yuri Gagarin-the first man into space, and the first lunar and planetary probes. This rocket is still in use today. These prestigious events attracted the attention of top politicians, along with additional funds for further research.
One problem that had not been solved was atmospheric reentry. It had been shown that an orbital vehicle easily had enough kinetic energy to vaporize itself, and yet it was known that meteorites can make it down to the ground. The mystery was solved in the US in 1951 when H. Julian Allen and A. J. Eggers, Jr. of the National Advisory Committee for Aeronautics (NACA) made the counterintuitive discovery[64] that a blunt shape (high drag) permitted the most effective heat shield. With this type of shape, around 99% of the energy goes into the air rather than vehicle, and this permitted safe recovery of orbital vehicles.
The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958.[65] The Blunt Body Theory made possible the heat shield designs that were embodied in the Mercury and all other space capsules and space planes, enabling astronauts to survive the fiery re-entry into Earth's atmosphere.
Rockets became extremely important militarily as modern intercontinental ballistic missiles (ICBMs) when it was realized that nuclear weapons carried on a rocket vehicle were essentially impossible for existing defense systems to stop once launched, and ICBM/Launch vehicles such as the R-7, Atlas and Titan became the delivery platform of choice for these weapons.
Fueled partly by the Cold War, the 1960s became the decade of rapid development of rocket technology particularly in the Soviet Union (Vostok, Soyuz, Proton) and in the United States (e.g. the X-15[66] and X-20 Dyna-Soar[67] aircraft). There was also significant research in other countries, such as Britain, Japan, Australia, etc., and a growing use of rockets for Space exploration, with pictures returned from the far side of the Moon and unmanned flights for Mars exploration.
In America the manned programmes, Project Mercury, Project Gemini and later the Apollo programme culminated in 1969 with the first manned landing on the moon via the Saturn V, causing the New York Times to retract their earlier editorial implying that spaceflight couldn't work:
—New York Times, 17 June 1969 - A Correction[68]
In the 1970s America made further lunar landings, before cancelling the Apollo programme in 1975. The replacement vehicle, the partially reusable 'Space Shuttle' was intended to be cheaper,[69] but this large reduction in costs was largely not achieved. Meanwhile in 1973, the expendable Ariane programme was begun, a launcher that by the year 2000 would capture much of the geosat market.
Rockets remain a popular military weapon. The use of large battlefield rockets of the V-2 type has given way to guided missiles. However rockets are often used by helicopters and light aircraft for ground attack, being more powerful than machine guns, but without the recoil of a heavy cannon and by the early 1960s air-to-air missiles became favored. Shoulder-launched rocket weapons are widespread in the anti-tank role due to their simplicity, low cost, light weight, accuracy and high level of damage. Current artillery systems such as the MLRS or BM-30 Smerch launch multiple rockets to saturate battlefield targets with munitions.[citation needed]
Commercially, rocketry is the enabler of all space technologies particularly satellites, many of which impact people's everyday lives in almost countless ways.[70]
Scientifically, rocketry has opened a window on the universe, allowing the launch of space probes to explore the solar system and space-based telescopes to obtain a clearer view of the rest of the universe.[71]
However, it is probably manned spaceflight that has predominantly caught the imagination of the public. Vehicles such as the Space Shuttle for scientific research, the Soyuz increasingly for orbital tourism and SpaceShipOne for suborbital tourism may show a trend towards greater commercialisation of manned rocketry.[72]
Rocket vehicles are often constructed in the archetypal tall thin "rocket" shape that takes off vertically, but there are actually many different types of rockets including:[73][74]
A rocket design can be as simple as a cardboard tube filled with black powder, but to make an efficient, accurate rocket or missile involves overcoming a number of difficult problems. The main difficulties include cooling the combustion chamber, pumping the fuel (in the case of a liquid fuel), and controlling and correcting the direction of motion.[78]
Rockets consist of a propellant, a place to put propellant (such as a propellant tank), and a nozzle. They may also have one or more rocket engines, directional stabilization device(s) (such as fins, vernier engines or engine gimbals for thrust vectoring, gyroscopes) and a structure (typically monocoque) to hold these components together. Rockets intended for high speed atmospheric use also have an aerodynamic fairing such as a nose cone, which usually holds the payload.[79]
As well as these components, rockets can have any number of other components, such as wings (rocketplanes), parachutes, wheels (rocket cars), even, in a sense, a person (rocket belt). Vehicles frequently possess navigation systems and guidance systems that typically use satellite navigation and inertial navigation systems.
Rocket engines employ the principle of jet propulsion.[1] The rocket engines powering rockets come in a great variety of different types, a comprehensive list can be found in rocket engine. Most current rockets are chemically powered rockets (usually internal combustion engines,[80] but some employ a decomposing monopropellant) that emit a hot exhaust gas. A rocket engine can use gas propellants, solid propellant, liquid propellant, or a hybrid mixture of both solid and liquid.[1] Some rockets use heat or pressure that is supplied from a source other than the chemical reaction of propellant(s), such as steam rockets, solar thermal rockets, nuclear thermal rocket engines or simple pressurized rockets such as water rocket or cold gas thrusters.[1] With combustive propellants a chemical reaction is initiated between the fuel and the oxidizer in the combustion chamber, and the resultant hot gases accelerate out of a rocket engine nozzle (or nozzles) at the rearward-facing end of the rocket. The acceleration of these gases through the engine exerts force ("thrust") on the combustion chamber and nozzle, propelling the vehicle (according to Newton's Third Law).[1] This actually happens because the force (pressure times area) on the combustion chamber wall is unbalanced by the nozzle opening; this is not the case in any other direction. The shape of the nozzle also generates force by directing the exhaust gas along the axis of the rocket.
Rocket propellant is mass that is stored, usually in some form of propellant tank or casing, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust.[1] For chemical rockets often the propellants are a fuel such as liquid hydrogen or kerosene burned with an oxidizer such as liquid oxygen or nitric acid to produce large volumes of very hot gas. The oxidiser is either kept separate and mixed in the combustion chamber, or comes premixed, as with solid rockets.
Sometimes the propellant is not burned but still undergoes a chemical reaction, and can be a 'monopropellant' such as hydrazine, nitrous oxide or hydrogen peroxide that can be catalytically decomposed to hot gas.
Alternatively, an inert propellant can be used that can be externally heated, such as in steam rocket, solar thermal rocket or nuclear thermal rockets.[1]
For smaller, low performance rockets such as attitude control thrusters where high performance is less necessary, a pressurised fluid is used as propellant that simply escapes the spacecraft through a propelling nozzle.[1]
Rockets or other similar reaction devices carrying their own propellant must be used when there is no other substance (land, water, or air) or force (gravity, magnetism, light) that a vehicle may usefully employ for propulsion, such as in space. In these circumstances, it is necessary to carry all the propellant to be used.
However, they are also useful in other situations:
Some military weapons use rockets to propel warheads to their targets. A rocket and its payload together are generally referred to as a missile when the weapon has a guidance system (not all missiles use rocket engines, some use other engines such as jets) or as a rocket if it is unguided. Anti-tank and anti-aircraft missiles use rocket engines to engage targets at high speed at a range of several miles, while intercontinental ballistic missiles can be used to deliver multiple nuclear warheads from thousands of miles, and anti-ballistic missiles try to stop them.
Sounding rockets are commonly used to carry instruments that take readings from 50 kilometres (31 mi) to 1,500 kilometres (930 mi) above the surface of the Earth, the altitudes between those reachable by weather balloons and satellites.[81]
Rocket engines are also used to propel rocket sleds along a rail at extremely high speed. The world record for this is Mach 8.5.[82]
Larger rockets are normally launched from a launch pad that provides stable support until a few seconds after ignition. Due to their high exhaust velocity—2,500 to 4,500 m/s (9,000 to 16,000 km/h; 5,600 to 10,000 mph) (Mach ~10+)—rockets are particularly useful when very high speeds are required, such as orbital speed (Mach 24+[83]). Spacecraft delivered into orbital trajectories become artificial satellites, which are used for many commercial purposes. Indeed, rockets remain the only way to launch spacecraft into orbit and beyond.[84] They are also used to rapidly accelerate spacecraft when they change orbits or de-orbit for landing. Also, a rocket may be used to soften a hard parachute landing immediately before touchdown (see retrorocket).
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